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    <link:label id="lab_us-gaap_CommonStockParOrStatedValuePerShare_ae26ed63-ee5c-43ef-a35a-6309174bc95e_terseLabel_en-US" xlink:label="lab_us-gaap_CommonStockParOrStatedValuePerShare" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Common stock, par value (in dollars per share)</link:label>
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    <link:label id="lab_mrk_EmergingMarketsEquitiesInvestmentFundsMember_1b3f37d0-a94d-4fe3-96e6-4ea93e69e59d_terseLabel_en-US" xlink:label="lab_mrk_EmergingMarketsEquitiesInvestmentFundsMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Emerging markets equities, Investment funds</link:label>
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    <link:label id="lab_us-gaap_OtherLiabilitiesNoncurrent_ff28fb54-5b44-433e-b2ee-996b47f5efa6_terseLabel_en-US" xlink:label="lab_us-gaap_OtherLiabilitiesNoncurrent" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Other Noncurrent Liabilities</link:label>
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    <link:label id="lab_us-gaap_MarketableSecuritiesCurrent_58fd9231-c12a-48b3-8945-4161f8ddeb67_terseLabel_en-US" xlink:label="lab_us-gaap_MarketableSecuritiesCurrent" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Short-term investments</link:label>
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    <link:label id="lab_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedInPeriodFairValue1_df06131c-b85c-4510-b2e2-21af9aa8bf8b_terseLabel_en-US" xlink:label="lab_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedInPeriodFairValue1" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Fair value of stock options vested</link:label>
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    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementLineItems"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_StatementLineItems" xlink:to="lab_us-gaap_StatementLineItems" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_DerivativeInstrumentsGainLossReclassificationFromAccumulatedOCIToIncomeEstimatedNetAmountToBeTransferred_4a96a56c-f8e0-4da1-ac28-566169ddcaa5_terseLabel_en-US" xlink:label="lab_us-gaap_DerivativeInstrumentsGainLossReclassificationFromAccumulatedOCIToIncomeEstimatedNetAmountToBeTransferred" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Pre tax net unrealized gain (loss) on derivatives maturing within next 12 months estimated to be reclassified from AOCI to sales</link:label>
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    <link:label id="lab_mrk_AnimalHealthsegmentMember_c74e63c2-d85e-4860-af98-4c150909c6da_terseLabel_en-US" xlink:label="lab_mrk_AnimalHealthsegmentMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Animal Health</link:label>
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    <link:label id="lab_us-gaap_LesseeOperatingLeaseRenewalTerm_226b6544-0ade-44ff-adc5-c619b50eebc7_terseLabel_en-US" xlink:label="lab_us-gaap_LesseeOperatingLeaseRenewalTerm" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Lessee, operating lease, renewal term</link:label>
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    <link:label id="lab_mrk_HealthcareServicesSegmentMember_ddd8df8e-fcd0-43fb-91d2-59780c447499_terseLabel_en-US" xlink:label="lab_mrk_HealthcareServicesSegmentMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Healthcare Services</link:label>
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    <link:label id="lab_us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustment_be30d3ed-47b4-40e4-ae4e-e73a7588af68_terseLabel_en-US" xlink:label="lab_us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustment" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Common shares issuable (in shares)</link:label>
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    <link:label id="lab_us-gaap_PropertyPlantAndEquipmentByTypeAxis_03455526-7406-4a42-afc9-ad76bff24d44_terseLabel_en-US" xlink:label="lab_us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Property, Plant and Equipment, Type [Axis]</link:label>
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    <link:label id="lab_us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent_50a637b5-c060-400d-913f-68ca8755b26c_terseLabel_en-US" xlink:label="lab_us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Allowance for doubtful accounts</link:label>
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    <link:label id="lab_us-gaap_IncomeStatementLocationDomain_f3e5a36d-9c54-4ad2-b114-6e03c754fa57_terseLabel_en-US" xlink:label="lab_us-gaap_IncomeStatementLocationDomain" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Income Statement Location [Domain]</link:label>
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    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_IncomeStatementLocationDomain" xlink:to="lab_us-gaap_IncomeStatementLocationDomain" xlink:type="arc" order="1"/>
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    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="lab_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_SellingGeneralAndAdministrativeExpense_b276da3f-1304-4976-9018-7cf032df897d_terseLabel_en-US" xlink:label="lab_us-gaap_SellingGeneralAndAdministrativeExpense" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Selling, general and administrative</link:label>
    <link:label id="lab_us-gaap_SellingGeneralAndAdministrativeExpense_label_en-US" xlink:label="lab_us-gaap_SellingGeneralAndAdministrativeExpense" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Selling, General and Administrative Expense</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingGeneralAndAdministrativeExpense" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SellingGeneralAndAdministrativeExpense"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_SellingGeneralAndAdministrativeExpense" xlink:to="lab_us-gaap_SellingGeneralAndAdministrativeExpense" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_ForeignExchangeContractMember_ac6c00e8-b51b-4798-bdff-5c0ca105966a_terseLabel_en-US" xlink:label="lab_us-gaap_ForeignExchangeContractMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Foreign exchange contracts</link:label>
    <link:label id="lab_us-gaap_ForeignExchangeContractMember_label_en-US" xlink:label="lab_us-gaap_ForeignExchangeContractMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Foreign Exchange Contract [Member]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignExchangeContractMember" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ForeignExchangeContractMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ForeignExchangeContractMember" xlink:to="lab_us-gaap_ForeignExchangeContractMember" xlink:type="arc" order="1"/>
    <link:label id="lab_mrk_OtherPharmaceuticalMember_ef3cfb25-2d94-4dd1-83b3-3ad33696542f_terseLabel_en-US" xlink:label="lab_mrk_OtherPharmaceuticalMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Other pharmaceutical</link:label>
    <link:label id="lab_mrk_OtherPharmaceuticalMember_label_en-US" xlink:label="lab_mrk_OtherPharmaceuticalMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Other Pharmaceutical [Member]</link:label>
    <link:label id="lab_mrk_OtherPharmaceuticalMember_documentation_en-US" xlink:label="lab_mrk_OtherPharmaceuticalMember" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Other pharmaceutical.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_mrk_OtherPharmaceuticalMember" xlink:href="mrk-20201231.xsd#mrk_OtherPharmaceuticalMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_mrk_OtherPharmaceuticalMember" xlink:to="lab_mrk_OtherPharmaceuticalMember" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearThree_b60c5ebb-8a5c-4917-8db1-86e400520198_terseLabel_en-US" xlink:label="lab_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearThree" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">2023</link:label>
    <link:label id="lab_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearThree_label_en-US" xlink:label="lab_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearThree" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Lessee, Operating Lease, Liability, to be Paid, Year Three</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearThree" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearThree"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearThree" xlink:to="lab_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearThree" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_OtherAssetsNoncurrent_ba195d29-3e36-457a-b2e4-f2613537414a_terseLabel_en-US" xlink:label="lab_us-gaap_OtherAssetsNoncurrent" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Other assets</link:label>
    <link:label id="lab_us-gaap_OtherAssetsNoncurrent_label_en-US" xlink:label="lab_us-gaap_OtherAssetsNoncurrent" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Other Assets, Noncurrent</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssetsNoncurrent" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherAssetsNoncurrent"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_OtherAssetsNoncurrent" xlink:to="lab_us-gaap_OtherAssetsNoncurrent" xlink:type="arc" order="1"/>
    <link:label id="lab_mrk_SixPointThreePercentageDebenturesDueOnTwoThousandAndTwentySixMember_bbbf8d86-ed05-48cf-b0b4-28a6c4b69583_terseLabel_en-US" xlink:label="lab_mrk_SixPointThreePercentageDebenturesDueOnTwoThousandAndTwentySixMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">6.30% debentures due 2026</link:label>
    <link:label id="lab_mrk_SixPointThreePercentageDebenturesDueOnTwoThousandAndTwentySixMember_label_en-US" xlink:label="lab_mrk_SixPointThreePercentageDebenturesDueOnTwoThousandAndTwentySixMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Six Point Three Percentage Debentures Due On Two Thousand And Twenty Six [Member]</link:label>
    <link:label id="lab_mrk_SixPointThreePercentageDebenturesDueOnTwoThousandAndTwentySixMember_documentation_en-US" xlink:label="lab_mrk_SixPointThreePercentageDebenturesDueOnTwoThousandAndTwentySixMember" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Six point three percentage debentures due on two thousand and twenty six.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_mrk_SixPointThreePercentageDebenturesDueOnTwoThousandAndTwentySixMember" xlink:href="mrk-20201231.xsd#mrk_SixPointThreePercentageDebenturesDueOnTwoThousandAndTwentySixMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_mrk_SixPointThreePercentageDebenturesDueOnTwoThousandAndTwentySixMember" xlink:to="lab_mrk_SixPointThreePercentageDebenturesDueOnTwoThousandAndTwentySixMember" xlink:type="arc" order="1"/>
    <link:label id="lab_mrk_NuvaringMember_4a3dbda8-953b-4c39-96e8-9754ae258b94_terseLabel_en-US" xlink:label="lab_mrk_NuvaringMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">NuvaRing</link:label>
    <link:label id="lab_mrk_NuvaringMember_label_en-US" xlink:label="lab_mrk_NuvaringMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Nuvaring [Member]</link:label>
    <link:label id="lab_mrk_NuvaringMember_documentation_en-US" xlink:label="lab_mrk_NuvaringMember" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">NuvaRing [Member].</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_mrk_NuvaringMember" xlink:href="mrk-20201231.xsd#mrk_NuvaringMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_mrk_NuvaringMember" xlink:to="lab_mrk_NuvaringMember" xlink:type="arc" order="1"/>
    <link:label id="lab_mrk_LongTermDebtExcludingCurrentMaturitiesMember_5f7a6a92-85ef-4d71-81ab-a19f52215c81_terseLabel_en-US" xlink:label="lab_mrk_LongTermDebtExcludingCurrentMaturitiesMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Long-Term Debt</link:label>
    <link:label id="lab_mrk_LongTermDebtExcludingCurrentMaturitiesMember_label_en-US" xlink:label="lab_mrk_LongTermDebtExcludingCurrentMaturitiesMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Long Term Debt Excluding Current Maturities [Member]</link:label>
    <link:label id="lab_mrk_LongTermDebtExcludingCurrentMaturitiesMember_documentation_en-US" xlink:label="lab_mrk_LongTermDebtExcludingCurrentMaturitiesMember" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Long Term Debt Excluding Current Maturities [Member]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_mrk_LongTermDebtExcludingCurrentMaturitiesMember" xlink:href="mrk-20201231.xsd#mrk_LongTermDebtExcludingCurrentMaturitiesMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_mrk_LongTermDebtExcludingCurrentMaturitiesMember" xlink:to="lab_mrk_LongTermDebtExcludingCurrentMaturitiesMember" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_Assets_50827914-f853-4a55-adf1-73fba98e474e_totalLabel_en-US" xlink:label="lab_us-gaap_Assets" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Total Assets</link:label>
    <link:label id="lab_us-gaap_Assets_label_en-US" xlink:label="lab_us-gaap_Assets" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Assets</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_Assets"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_Assets" xlink:to="lab_us-gaap_Assets" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_ImpairmentOfIntangibleAssetsIndefinitelivedExcludingGoodwill_314e1677-5316-4795-824e-36ad3c6ee25a_verboseLabel_en-US" xlink:label="lab_us-gaap_ImpairmentOfIntangibleAssetsIndefinitelivedExcludingGoodwill" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">IPR&amp;D impairment charges</link:label>
    <link:label id="lab_us-gaap_ImpairmentOfIntangibleAssetsIndefinitelivedExcludingGoodwill_label_en-US" xlink:label="lab_us-gaap_ImpairmentOfIntangibleAssetsIndefinitelivedExcludingGoodwill" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Impairment of Intangible Assets, Indefinite-lived (Excluding Goodwill)</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ImpairmentOfIntangibleAssetsIndefinitelivedExcludingGoodwill" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ImpairmentOfIntangibleAssetsIndefinitelivedExcludingGoodwill"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ImpairmentOfIntangibleAssetsIndefinitelivedExcludingGoodwill" xlink:to="lab_us-gaap_ImpairmentOfIntangibleAssetsIndefinitelivedExcludingGoodwill" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_ForeignGovernmentDebtSecuritiesMember_ddb9394f-2c94-4f94-88ef-b72586a760bd_terseLabel_en-US" xlink:label="lab_us-gaap_ForeignGovernmentDebtSecuritiesMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Foreign government bonds</link:label>
    <link:label id="lab_us-gaap_ForeignGovernmentDebtSecuritiesMember_label_en-US" xlink:label="lab_us-gaap_ForeignGovernmentDebtSecuritiesMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Debt Security, Government, Non-US [Member]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignGovernmentDebtSecuritiesMember" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ForeignGovernmentDebtSecuritiesMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ForeignGovernmentDebtSecuritiesMember" xlink:to="lab_us-gaap_ForeignGovernmentDebtSecuritiesMember" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_ad5eed60-6ede-4bd4-bd17-7c20a90fd8b4_periodStartLabel_en-US" xlink:label="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Number of Shares, Nonvested January 1</link:label>
    <link:label id="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_5711eb5c-e538-4357-a423-b215a06d4c55_periodEndLabel_en-US" xlink:label="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Number of Shares, Nonvested December 31</link:label>
    <link:label id="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_label_en-US" xlink:label="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber" xlink:to="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets_23856e04-f779-4008-a0eb-01daed151b79_verboseLabel_en-US" xlink:label="lab_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">In-process research and development (IPR&amp;D)</link:label>
    <link:label id="lab_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets_label_en-US" xlink:label="lab_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets" xlink:to="lab_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_RetirementPlanSponsorLocationAxis_d6b36fed-dd5d-4734-a7c7-e94c4fe5ab7a_terseLabel_en-US" xlink:label="lab_us-gaap_RetirementPlanSponsorLocationAxis" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Retirement Plan Sponsor Location [Axis]</link:label>
    <link:label id="lab_us-gaap_RetirementPlanSponsorLocationAxis_label_en-US" xlink:label="lab_us-gaap_RetirementPlanSponsorLocationAxis" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Retirement Plan Sponsor Location [Axis]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanSponsorLocationAxis" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RetirementPlanSponsorLocationAxis"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_RetirementPlanSponsorLocationAxis" xlink:to="lab_us-gaap_RetirementPlanSponsorLocationAxis" xlink:type="arc" order="1"/>
    <link:label id="lab_mrk_Pneumovax23Member_751e5527-b5be-498e-bf55-baa5dc7e70cd_terseLabel_en-US" xlink:label="lab_mrk_Pneumovax23Member" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Pneumovax 23</link:label>
    <link:label id="lab_mrk_Pneumovax23Member_label_en-US" xlink:label="lab_mrk_Pneumovax23Member" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Pneumovax 23 [Member]</link:label>
    <link:label id="lab_mrk_Pneumovax23Member_documentation_en-US" xlink:label="lab_mrk_Pneumovax23Member" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Pneumovax 23[Member].</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_mrk_Pneumovax23Member" xlink:href="mrk-20201231.xsd#mrk_Pneumovax23Member"/>
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    <link:label id="lab_us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit_e68ef48d-54d6-45d1-9b2d-dc8bfb097666_terseLabel_en-US" xlink:label="lab_us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Amortization of unrecognized prior service cost</link:label>
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    <link:label id="lab_us-gaap_IntangibleAssetsFiniteLivedPolicy_37c69c90-c70e-4125-91f2-9298bef2fcc3_terseLabel_en-US" xlink:label="lab_us-gaap_IntangibleAssetsFiniteLivedPolicy" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Acquired Intangibles</link:label>
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    <link:label id="lab_us-gaap_EquitySecuritiesFvNiUnrealizedGainLoss_032995bf-92fc-4b5b-b205-f38edb95630c_terseLabel_en-US" xlink:label="lab_us-gaap_EquitySecuritiesFvNiUnrealizedGainLoss" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Unrealized net gains</link:label>
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    <link:label id="lab_us-gaap_OtherIntangibleAssetsMember_5c1c4ae0-0c44-4e63-b783-365c83720fcf_terseLabel_en-US" xlink:label="lab_us-gaap_OtherIntangibleAssetsMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Other</link:label>
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    <link:label id="lab_mrk_CubicinMember_84cacef4-7694-4fdb-9ead-4303fd773116_terseLabel_en-US" xlink:label="lab_mrk_CubicinMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Cubicin</link:label>
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    <link:label id="lab_us-gaap_Liabilities_f013c546-6e74-4c2d-b51a-debb6c43239f_terseLabel_en-US" xlink:label="lab_us-gaap_Liabilities" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Liabilities</link:label>
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    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Liabilities" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_Liabilities"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_Liabilities" xlink:to="lab_us-gaap_Liabilities" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_IncomeTaxContingencyLineItems_eb6c309e-c534-4c61-8a91-cf8c37ddc756_terseLabel_en-US" xlink:label="lab_us-gaap_IncomeTaxContingencyLineItems" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Income Tax Contingency [Line Items]</link:label>
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    <link:label id="lab_us-gaap_SalesMember_b6224db9-685d-433f-83b8-679e861c09d3_verboseLabel_en-US" xlink:label="lab_us-gaap_SalesMember" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Total sales</link:label>
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    <link:label id="lab_mrk_EmendMember_ab40f533-036d-4b4b-bc09-3d218b68667b_terseLabel_en-US" xlink:label="lab_mrk_EmendMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Emend</link:label>
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    <link:label id="lab_us-gaap_RetirementPlanTypeAxis_469d20ec-6986-452e-9a6a-010404c38c60_terseLabel_en-US" xlink:label="lab_us-gaap_RetirementPlanTypeAxis" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Retirement Plan Type [Axis]</link:label>
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    <link:label id="lab_us-gaap_FairValueInputsLevel1Member_1a9d2aeb-47d1-49a7-8725-5a9f0c0b30e6_terseLabel_en-US" xlink:label="lab_us-gaap_FairValueInputsLevel1Member" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Level 1</link:label>
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    <link:label id="lab_us-gaap_LegalEntityTypeOfCounterpartyDomain_f9dfd8c6-7507-4bb8-b55c-afe89be8086c_terseLabel_en-US" xlink:label="lab_us-gaap_LegalEntityTypeOfCounterpartyDomain" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Legal Entity Type of Counterparty [Domain]</link:label>
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    <link:label id="lab_mrk_IsentressIsentressHDMember_688d8ad2-bafd-4c65-a7b6-b470ebffa57d_terseLabel_en-US" xlink:label="lab_mrk_IsentressIsentressHDMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Isentress/Isentress HD</link:label>
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    <link:label id="lab_us-gaap_EquitySecuritiesFvNi_5de510fe-4745-4290-b5b7-04623ed54b75_verboseLabel_en-US" xlink:label="lab_us-gaap_EquitySecuritiesFvNi" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Publicly traded equity securities, fair value</link:label>
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    <link:label id="lab_mrk_FosamaxMember_15958226-27f5-4c63-be3d-2ad9cd7704c4_terseLabel_en-US" xlink:label="lab_mrk_FosamaxMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Fosamax</link:label>
    <link:label id="lab_mrk_FosamaxMember_label_en-US" xlink:label="lab_mrk_FosamaxMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Fosamax [Member]</link:label>
    <link:label id="lab_mrk_FosamaxMember_documentation_en-US" xlink:label="lab_mrk_FosamaxMember" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Fosamax [Member].</link:label>
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    <link:label id="lab_mrk_OtherNonoperatingIncomeExpenseOther_e4822ddd-a130-4338-883b-8e0da1fd6134_negatedLabel_en-US" xlink:label="lab_mrk_OtherNonoperatingIncomeExpenseOther" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Other, net</link:label>
    <link:label id="lab_mrk_OtherNonoperatingIncomeExpenseOther_label_en-US" xlink:label="lab_mrk_OtherNonoperatingIncomeExpenseOther" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Other Nonoperating Income Expense, Other</link:label>
    <link:label id="lab_mrk_OtherNonoperatingIncomeExpenseOther_documentation_en-US" xlink:label="lab_mrk_OtherNonoperatingIncomeExpenseOther" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Other nonoperating income and expense items not separately disclosed.</link:label>
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    <link:label id="lab_mrk_CGRPreceptorantagonistsMember_d8137f7d-819c-48cc-bac6-524efd020aee_terseLabel_en-US" xlink:label="lab_mrk_CGRPreceptorantagonistsMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">CGRP receptor antagonists</link:label>
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    <link:label id="lab_us-gaap_DesignatedAsHedgingInstrumentMember_b0deab99-9463-48ed-8f2e-2b62c2172734_terseLabel_en-US" xlink:label="lab_us-gaap_DesignatedAsHedgingInstrumentMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Derivatives Designated as Hedging Instruments</link:label>
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    <link:label id="lab_us-gaap_InventoryNoncurrent_a81fc772-b92d-49bf-b8ac-8d4a7da427b3_terseLabel_en-US" xlink:label="lab_us-gaap_InventoryNoncurrent" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Inventory, Noncurrent</link:label>
    <link:label id="lab_us-gaap_InventoryNoncurrent_b7602714-f594-4faf-a104-24fa2e3db0f1_verboseLabel_en-US" xlink:label="lab_us-gaap_InventoryNoncurrent" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Other assets</link:label>
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    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InventoryNoncurrent" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_InventoryNoncurrent"/>
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    <link:label id="lab_us-gaap_GoodwillAcquiredDuringPeriod_5255f93c-0a23-40ba-bd8a-367e4edbb744_terseLabel_en-US" xlink:label="lab_us-gaap_GoodwillAcquiredDuringPeriod" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Acquisitions</link:label>
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    <link:label id="lab_us-gaap_ScheduleOfRestructuringAndRelatedCostsTextBlock_db2becef-dbcd-4c94-a2ea-65c8f35fab47_terseLabel_en-US" xlink:label="lab_us-gaap_ScheduleOfRestructuringAndRelatedCostsTextBlock" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Charges Related to Restructuring Program Activities by Type of Cost</link:label>
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    <link:label id="lab_mrk_RestructuringReserveNoncashActivity_label_en-US" xlink:label="lab_mrk_RestructuringReserveNoncashActivity" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Restructuring Reserve Noncash Activity</link:label>
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    <link:label id="lab_us-gaap_EquitySecuritiesWithoutReadilyDeterminableFairValueDownwardPriceAdjustmentCumulativeAmount_cf0f844b-a960-48e8-a958-1b762b7ebfb2_terseLabel_en-US" xlink:label="lab_us-gaap_EquitySecuritiesWithoutReadilyDeterminableFairValueDownwardPriceAdjustmentCumulativeAmount" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Cumulative downward price adjustment</link:label>
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    <link:label id="lab_mrk_KeytrudaMember_b56b39c2-e370-4af4-a15a-6cb47b83e8c5_terseLabel_en-US" xlink:label="lab_mrk_KeytrudaMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Keytruda</link:label>
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    <link:label id="lab_mrk_KeytrudaMember_documentation_en-US" xlink:label="lab_mrk_KeytrudaMember" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Keytruda [Member]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_mrk_KeytrudaMember" xlink:href="mrk-20201231.xsd#mrk_KeytrudaMember"/>
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    <link:label id="lab_us-gaap_ScheduleOfOtherDerivativesNotDesignatedAsHedgingInstrumentsStatementsOfFinancialPerformanceAndFinancialPositionLocationTableTextBlock_94c4fc28-c51c-48ff-af8e-2970659abbc1_terseLabel_en-US" xlink:label="lab_us-gaap_ScheduleOfOtherDerivativesNotDesignatedAsHedgingInstrumentsStatementsOfFinancialPerformanceAndFinancialPositionLocationTableTextBlock" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Income Statement Effects of Derivatives Not Designated as Hedging Instruments</link:label>
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    <link:label id="lab_us-gaap_PropertyPlantAndEquipmentUsefulLife_19d3a6de-c1b3-4d61-8c76-8e369b4505b1_terseLabel_en-US" xlink:label="lab_us-gaap_PropertyPlantAndEquipmentUsefulLife" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Estimated useful life of property, plant and equipment</link:label>
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    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentUsefulLife" xlink:to="lab_us-gaap_PropertyPlantAndEquipmentUsefulLife" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_GoodwillLineItems_8081b3da-d4aa-4df4-98b1-ebadbbd2cafc_terseLabel_en-US" xlink:label="lab_us-gaap_GoodwillLineItems" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Goodwill [Line Items]</link:label>
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    <link:label id="lab_mrk_CancidasMember_documentation_en-US" xlink:label="lab_mrk_CancidasMember" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Cancidas [Member].</link:label>
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    <link:label id="lab_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_9afc460f-007c-4775-8a38-dafc2f51f451_negatedTerseLabel_en-US" xlink:label="lab_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax" xlink:role="http://www.xbrl.org/2009/role/negatedTerseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Debt securities, gross unrealized losses</link:label>
    <link:label id="lab_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_label_en-US" xlink:label="lab_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax"/>
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    <link:label id="lab_mrk_PelotonMember_22441c73-47fe-4282-8018-1940e0c21f1f_terseLabel_en-US" xlink:label="lab_mrk_PelotonMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Peloton</link:label>
    <link:label id="lab_mrk_PelotonMember_label_en-US" xlink:label="lab_mrk_PelotonMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Peloton [Member]</link:label>
    <link:label id="lab_mrk_PelotonMember_documentation_en-US" xlink:label="lab_mrk_PelotonMember" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Peloton [Member]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_mrk_PelotonMember" xlink:href="mrk-20201231.xsd#mrk_PelotonMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_mrk_PelotonMember" xlink:to="lab_mrk_PelotonMember" xlink:type="arc" order="1"/>
    <link:label id="lab_dei_EntityAddressPostalZipCode_70fea470-00b0-489d-a595-84590b5079a9_terseLabel_en-US" xlink:label="lab_dei_EntityAddressPostalZipCode" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Entity Address, Postal Zip Code</link:label>
    <link:label id="lab_dei_EntityAddressPostalZipCode_label_en-US" xlink:label="lab_dei_EntityAddressPostalZipCode" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Entity Address, Postal Zip Code</link:label>
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    <link:label id="lab_us-gaap_DeferredTaxAssetsNet_d8939cdc-6673-4ca7-a7c5-241230aab2a6_totalLabel_en-US" xlink:label="lab_us-gaap_DeferredTaxAssetsNet" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Total deferred taxes</link:label>
    <link:label id="lab_us-gaap_DeferredTaxAssetsNet_label_en-US" xlink:label="lab_us-gaap_DeferredTaxAssetsNet" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Deferred Tax Assets, Net of Valuation Allowance</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredTaxAssetsNet" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DeferredTaxAssetsNet"/>
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    <link:label id="lab_mrk_DevelopedMarketsEquitiesInvestmentFundsMember_926ac19d-4e98-48fe-bf00-482c2263a760_terseLabel_en-US" xlink:label="lab_mrk_DevelopedMarketsEquitiesInvestmentFundsMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Developed markets equities, Investment funds</link:label>
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    <link:label id="lab_mrk_DevelopedMarketsEquitiesInvestmentFundsMember_documentation_en-US" xlink:label="lab_mrk_DevelopedMarketsEquitiesInvestmentFundsMember" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Developed markets equities investment funds.</link:label>
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    <link:label id="lab_us-gaap_RestructuringCostAndReserveAxis_acd2e7ca-5d78-4f55-9666-8c4ad1cfaa13_terseLabel_en-US" xlink:label="lab_us-gaap_RestructuringCostAndReserveAxis" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Restructuring Type [Axis]</link:label>
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    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_RestructuringCostAndReserveAxis" xlink:to="lab_us-gaap_RestructuringCostAndReserveAxis" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_Goodwill_a04905ee-e9f8-4e20-809f-faba07cdb78a_terseLabel_en-US" xlink:label="lab_us-gaap_Goodwill" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Goodwill</link:label>
    <link:label id="lab_us-gaap_Goodwill_2c84e29f-3c79-4d43-868a-e08cd41ce95b_periodStartLabel_en-US" xlink:label="lab_us-gaap_Goodwill" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Goodwill, Beginning Balance</link:label>
    <link:label id="lab_us-gaap_Goodwill_513be7f2-0397-49d0-bb11-ea00127880c5_periodEndLabel_en-US" xlink:label="lab_us-gaap_Goodwill" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Goodwill, Ending Balance</link:label>
    <link:label id="lab_us-gaap_Goodwill_label_en-US" xlink:label="lab_us-gaap_Goodwill" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Goodwill</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_Goodwill"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_Goodwill" xlink:to="lab_us-gaap_Goodwill" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_2ad5bdf2-aa34-4244-94b2-ecd3f4fce7ce_terseLabel_en-US" xlink:label="lab_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Debt Securities, Available-for-sale [Line Items]</link:label>
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    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems"/>
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    <link:label id="lab_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_12114fd2-391e-43af-af15-19909bfb1a25_totalLabel_en-US" xlink:label="lab_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Other comprehensive income (loss), net of taxes</link:label>
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    <link:label id="lab_mrk_CostsExpensesAndOther_de3cd0ac-96aa-4daf-9cba-6f0ea7111341_totalLabel_en-US" xlink:label="lab_mrk_CostsExpensesAndOther" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Total costs, expenses and other</link:label>
    <link:label id="lab_mrk_CostsExpensesAndOther_label_en-US" xlink:label="lab_mrk_CostsExpensesAndOther" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Costs Expenses And Other</link:label>
    <link:label id="lab_mrk_CostsExpensesAndOther_documentation_en-US" xlink:label="lab_mrk_CostsExpensesAndOther" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Total of cost of sales, operating expenses and nonoperating income or expense.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_mrk_CostsExpensesAndOther" xlink:href="mrk-20201231.xsd#mrk_CostsExpensesAndOther"/>
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    <link:label id="lab_mrk_MortgageAndAssetBackedSecuritiesInvestmentFundsMember_df95f893-4716-4e15-bdfd-9f832e01e569_terseLabel_en-US" xlink:label="lab_mrk_MortgageAndAssetBackedSecuritiesInvestmentFundsMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Mortgage and Asset-Backed Securities Investment Funds</link:label>
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    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_mrk_MortgageAndAssetBackedSecuritiesInvestmentFundsMember" xlink:to="lab_mrk_MortgageAndAssetBackedSecuritiesInvestmentFundsMember" xlink:type="arc" order="1"/>
    <link:label id="lab_mrk_IOmetPharmaLtdMember_3336229e-b7f2-4395-8a35-4b4b6b82d6ab_terseLabel_en-US" xlink:label="lab_mrk_IOmetPharmaLtdMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">IOmet Pharma Ltd</link:label>
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    <link:label id="lab_mrk_IOmetPharmaLtdMember_documentation_en-US" xlink:label="lab_mrk_IOmetPharmaLtdMember" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">IOmet Pharma Ltd [Member]</link:label>
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    <link:label id="lab_us-gaap_ArrangementsAndNonarrangementTransactionsMember_74eb0f9d-b97a-4ac2-bec6-d8fd6ba9a11d_terseLabel_en-US" xlink:label="lab_us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Collaborative Arrangement and Arrangement Other than Collaborative [Domain]</link:label>
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    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:to="lab_us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_BusinessAcquisitionCostOfAcquiredEntityTransactionCosts_1d03a59c-d879-472f-90c5-095d46299ed6_terseLabel_en-US" xlink:label="lab_us-gaap_BusinessAcquisitionCostOfAcquiredEntityTransactionCosts" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Transaction costs</link:label>
    <link:label id="lab_us-gaap_BusinessAcquisitionCostOfAcquiredEntityTransactionCosts_label_en-US" xlink:label="lab_us-gaap_BusinessAcquisitionCostOfAcquiredEntityTransactionCosts" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Business Acquisition, Transaction Costs</link:label>
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    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_BusinessAcquisitionCostOfAcquiredEntityTransactionCosts" xlink:to="lab_us-gaap_BusinessAcquisitionCostOfAcquiredEntityTransactionCosts" xlink:type="arc" order="1"/>
    <link:label id="lab_mrk_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresTableTextBlock_4c8ac3d0-5d73-485d-aa90-d06b40951abe_terseLabel_en-US" xlink:label="lab_mrk_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresTableTextBlock" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Additional Information Pertaining to Stock Option Plans</link:label>
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    <link:label id="lab_mrk_RegulatoryMilestonesMember_e2c8c6a2-521b-41b4-ac18-6e3a7fd0389c_terseLabel_en-US" xlink:label="lab_mrk_RegulatoryMilestonesMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Regulatory Milestones</link:label>
    <link:label id="lab_mrk_RegulatoryMilestonesMember_label_en-US" xlink:label="lab_mrk_RegulatoryMilestonesMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Regulatory Milestones [Member]</link:label>
    <link:label id="lab_mrk_RegulatoryMilestonesMember_documentation_en-US" xlink:label="lab_mrk_RegulatoryMilestonesMember" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Regulatory Milestones [Member]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_mrk_RegulatoryMilestonesMember" xlink:href="mrk-20201231.xsd#mrk_RegulatoryMilestonesMember"/>
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    <link:label id="lab_us-gaap_IncreaseDecreaseInAccruedIncomeTaxesPayable_20fe2e3c-fd6f-48e2-8e59-a4168d1cb301_terseLabel_en-US" xlink:label="lab_us-gaap_IncreaseDecreaseInAccruedIncomeTaxesPayable" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Income taxes payable</link:label>
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    <link:label id="lab_us-gaap_CommonStockDividendsPerShareDeclared_72a74231-98ad-4bf4-bd56-4e928ae2a4b9_terseLabel_en-US" xlink:label="lab_us-gaap_CommonStockDividendsPerShareDeclared" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Common stock, dividends declared (in dollars per share)</link:label>
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    <link:label id="lab_us-gaap_DebtInstrumentFaceAmount_b4d644b4-01e3-4bf5-add2-31873c1e9704_verboseLabel_en-US" xlink:label="lab_us-gaap_DebtInstrumentFaceAmount" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Face amount of debt</link:label>
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    <link:label id="lab_mrk_RoyaltyRatePercentage_5c4e709a-da47-4502-b38c-dd68e379e159_terseLabel_en-US" xlink:label="lab_mrk_RoyaltyRatePercentage" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Royalty rate, percentage</link:label>
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    <link:label id="lab_mrk_RealEstateInvestmentFundsMember_6523d668-e2cf-4856-bc5f-4f62d0505ede_terseLabel_en-US" xlink:label="lab_mrk_RealEstateInvestmentFundsMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Real estate, Investment funds</link:label>
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    <link:label id="lab_mrk_RealEstateInvestmentFundsMember_label_en-US" xlink:label="lab_mrk_RealEstateInvestmentFundsMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Real Estate Investment Funds [Member]</link:label>
    <link:label id="lab_mrk_RealEstateInvestmentFundsMember_documentation_en-US" xlink:label="lab_mrk_RealEstateInvestmentFundsMember" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Real estate investment funds.</link:label>
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    <link:label id="lab_us-gaap_OtherAssetsCurrent_aa57d422-9827-4899-9111-178b6f01a815_terseLabel_en-US" xlink:label="lab_us-gaap_OtherAssetsCurrent" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Other current assets</link:label>
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    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_OtherAssetsCurrent" xlink:to="lab_us-gaap_OtherAssetsCurrent" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_BusinessCombinationContingentConsiderationLiabilityMeasurementInput_d982404b-b14c-453a-aead-7ac91940f403_terseLabel_en-US" xlink:label="lab_us-gaap_BusinessCombinationContingentConsiderationLiabilityMeasurementInput" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Business Combination, Contingent Consideration, Liability, Measurement Input</link:label>
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    <link:label id="lab_mrk_DunboyneMember_9aef168a-b7fa-4e2a-bf56-ebdcd1e5447e_terseLabel_en-US" xlink:label="lab_mrk_DunboyneMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Dunboyne</link:label>
    <link:label id="lab_mrk_DunboyneMember_label_en-US" xlink:label="lab_mrk_DunboyneMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Dunboyne [Member]</link:label>
    <link:label id="lab_mrk_DunboyneMember_documentation_en-US" xlink:label="lab_mrk_DunboyneMember" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Dunboyne</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_mrk_DunboyneMember" xlink:href="mrk-20201231.xsd#mrk_DunboyneMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_mrk_DunboyneMember" xlink:to="lab_mrk_DunboyneMember" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_ScheduleOfGoodwillTextBlock_12fc7176-b511-48c8-a851-394505c524f6_terseLabel_en-US" xlink:label="lab_us-gaap_ScheduleOfGoodwillTextBlock" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Goodwill Activity by Segment</link:label>
    <link:label id="lab_us-gaap_ScheduleOfGoodwillTextBlock_label_en-US" xlink:label="lab_us-gaap_ScheduleOfGoodwillTextBlock" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Schedule of Goodwill [Table Text Block]</link:label>
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    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ScheduleOfGoodwillTextBlock" xlink:to="lab_us-gaap_ScheduleOfGoodwillTextBlock" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_InventoryLIFOReserve_f3d9c7aa-08a9-4f2e-8439-8d1d33fb7105_negatedLabel_en-US" xlink:label="lab_us-gaap_InventoryLIFOReserve" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Decrease to LIFO cost</link:label>
    <link:label id="lab_us-gaap_InventoryLIFOReserve_label_en-US" xlink:label="lab_us-gaap_InventoryLIFOReserve" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Inventory, LIFO Reserve</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InventoryLIFOReserve" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_InventoryLIFOReserve"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_InventoryLIFOReserve" xlink:to="lab_us-gaap_InventoryLIFOReserve" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod_b4ed283e-2858-4db9-b8b5-00c51f3250fd_negatedLabel_en-US" xlink:label="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Number of Options, Forfeited (in shares)</link:label>
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    <link:label id="lab_us-gaap_EquityAbstract_91f55fc0-a4f5-48b2-950b-f4ca32fbe2b4_terseLabel_en-US" xlink:label="lab_us-gaap_EquityAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Equity [Abstract]</link:label>
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    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_EquityAbstract" xlink:to="lab_us-gaap_EquityAbstract" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_AssetsFairValueDisclosure_59dc1c80-498e-4809-bd96-92981725071c_totalLabel_en-US" xlink:label="lab_us-gaap_AssetsFairValueDisclosure" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Total assets</link:label>
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    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_AssetsFairValueDisclosure" xlink:to="lab_us-gaap_AssetsFairValueDisclosure" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_EMEAMember_0ba9f9bf-0c3d-4792-a8af-7ba0bd4e5d97_terseLabel_en-US" xlink:label="lab_us-gaap_EMEAMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Europe, Middle East and Africa</link:label>
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    <link:label id="lab_mrk_PrevymisMember_label_en-US" xlink:label="lab_mrk_PrevymisMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Prevymis [Member]</link:label>
    <link:label id="lab_mrk_PrevymisMember_documentation_en-US" xlink:label="lab_mrk_PrevymisMember" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Prevymis</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_mrk_PrevymisMember" xlink:href="mrk-20201231.xsd#mrk_PrevymisMember"/>
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    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanActualReturnOnPlanAssetsSoldDuringPeriod" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DefinedBenefitPlanActualReturnOnPlanAssetsSoldDuringPeriod"/>
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    <link:label id="lab_us-gaap_RestrictedStockUnitsRSUMember_656e7456-ff83-4bb9-96ca-852e2a3e89ec_terseLabel_en-US" xlink:label="lab_us-gaap_RestrictedStockUnitsRSUMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">RSUs</link:label>
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    <link:label id="lab_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearFive_5d235b5d-67a0-463f-9c2f-67fac976c9cc_terseLabel_en-US" xlink:label="lab_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearFive" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">2025</link:label>
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    <link:label id="lab_us-gaap_OtherAssetsMember_25961412-709f-4cc1-bb86-3052fce23442_terseLabel_en-US" xlink:label="lab_us-gaap_OtherAssetsMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Other Assets</link:label>
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    <link:label id="lab_us-gaap_FinancialInstrumentAxis_86de29ac-92ae-4d12-b67f-5c584c9d4d5d_terseLabel_en-US" xlink:label="lab_us-gaap_FinancialInstrumentAxis" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Financial Instrument [Axis]</link:label>
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    <link:label id="lab_us-gaap_TypeOfAdoptionMember_be5b611b-4273-48a8-a741-377c3b7820a2_terseLabel_en-US" xlink:label="lab_us-gaap_TypeOfAdoptionMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Type of Adoption [Domain]</link:label>
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    <link:label id="lab_mrk_CaliforniaStateCourtMember_documentation_en-US" xlink:label="lab_mrk_CaliforniaStateCourtMember" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">California state court.</link:label>
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    <link:label id="lab_mrk_RevenueRecognitionGoodsGoodsReturnPeriodAftertoExpirationDate_2817c2af-f2ff-43f5-a06b-7cb611d2a7e4_terseLabel_en-US" xlink:label="lab_mrk_RevenueRecognitionGoodsGoodsReturnPeriodAftertoExpirationDate" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Product return period and expiration</link:label>
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    <link:label id="lab_us-gaap_DeferredTaxAssetsValuationAllowance_01f0677b-780e-4fa7-821c-81afe147c73b_negatedLabel_en-US" xlink:label="lab_us-gaap_DeferredTaxAssetsValuationAllowance" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Valuation allowance, Assets</link:label>
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    <link:label id="lab_mrk_ScheduleOfOtherIntangiblesTable_documentation_en-US" xlink:label="lab_mrk_ScheduleOfOtherIntangiblesTable" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Schedule Of Other Intangibles [Table]</link:label>
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    <link:label id="lab_us-gaap_EquitySecuritiesWithoutReadilyDeterminableFairValueAmount_67dc7442-634c-46bf-9212-c661eba03883_terseLabel_en-US" xlink:label="lab_us-gaap_EquitySecuritiesWithoutReadilyDeterminableFairValueAmount" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Equity investments without readily determinable fair values</link:label>
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    <link:label id="lab_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_43c06a02-3b66-4e20-8622-c049cb73187f_totalLabel_en-US" xlink:label="lab_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Total equity</link:label>
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    <link:label id="lab_mrk_NewJerseyStateCourtMember_documentation_en-US" xlink:label="lab_mrk_NewJerseyStateCourtMember" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">New Jersey state court member.</link:label>
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    <link:label id="lab_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths_75522821-86e7-4298-a51e-55f6043782de_terseLabel_en-US" xlink:label="lab_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Estimated aggregate amortization expense, 2021</link:label>
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    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_Revenues" xlink:to="lab_us-gaap_Revenues" xlink:type="arc" order="1"/>
    <link:label id="lab_mrk_AdempasMember_9f5c37e8-9a3e-4675-a350-a38349af305c_terseLabel_en-US" xlink:label="lab_mrk_AdempasMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Adempas</link:label>
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    <link:label id="lab_mrk_AdempasMember_documentation_en-US" xlink:label="lab_mrk_AdempasMember" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Adempas</link:label>
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    <link:label id="lab_us-gaap_LiabilitiesFairValueDisclosure_21570463-3ccf-4e47-8bba-0b23d7f9d695_totalLabel_en-US" xlink:label="lab_us-gaap_LiabilitiesFairValueDisclosure" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Total liabilities</link:label>
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    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_LiabilitiesFairValueDisclosure" xlink:to="lab_us-gaap_LiabilitiesFairValueDisclosure" xlink:type="arc" order="1"/>
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    <link:label id="lab_dei_EntityAddressAddressLine1_8f5997a5-b410-44ee-9f25-619100937ad5_terseLabel_en-US" xlink:label="lab_dei_EntityAddressAddressLine1" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Entity Address, Address Line One</link:label>
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    <link:label id="lab_us-gaap_DeferredIncomeTaxExpenseBenefit_f2712749-5dd4-402f-8a90-2db986ca914c_terseLabel_en-US" xlink:label="lab_us-gaap_DeferredIncomeTaxExpenseBenefit" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Deferred income taxes</link:label>
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    <link:label id="lab_us-gaap_ImpairmentOfLongLivedAssetsToBeDisposedOf_10c682d6-5208-4934-891d-ce3102d22a68_terseLabel_en-US" xlink:label="lab_us-gaap_ImpairmentOfLongLivedAssetsToBeDisposedOf" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Write-down of assets held for sale</link:label>
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    <link:label id="lab_mrk_A1.375eurodenominatednotesdue2036Member_c57e57b4-4f6a-454e-a18f-58c7e60c6e20_terseLabel_en-US" xlink:label="lab_mrk_A1.375eurodenominatednotesdue2036Member" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">1.375% euro-denominated notes due 2036</link:label>
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    <link:label id="lab_srt_MaximumMember_c8c56b83-9756-43cc-971e-a88668947bcd_terseLabel_en-US" xlink:label="lab_srt_MaximumMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Maximum</link:label>
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    <link:label id="lab_us-gaap_PreferredStockSharesAuthorized_cb9adc31-8d85-4f43-a81a-e0c37b4b31e1_terseLabel_en-US" xlink:label="lab_us-gaap_PreferredStockSharesAuthorized" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Preferred stock, shares authorized</link:label>
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    <link:label id="lab_us-gaap_NoncontrollingInterestMember_0d1fe0c4-1388-4833-a8d6-579355bc5725_terseLabel_en-US" xlink:label="lab_us-gaap_NoncontrollingInterestMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Non- controlling Interests</link:label>
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    <link:label id="lab_us-gaap_EffectiveIncomeTaxRateContinuingOperations_6cb002d2-4bd7-4e53-83c7-e2cb242950c6_totalLabel_en-US" xlink:label="lab_us-gaap_EffectiveIncomeTaxRateContinuingOperations" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Total, Tax Rate</link:label>
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    <link:label id="lab_us-gaap_FairValueMeasurementsRecurringMember_label_en-US" xlink:label="lab_us-gaap_FairValueMeasurementsRecurringMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Fair Value, Recurring [Member]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsRecurringMember" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueMeasurementsRecurringMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_FairValueMeasurementsRecurringMember" xlink:to="lab_us-gaap_FairValueMeasurementsRecurringMember" xlink:type="arc" order="1"/>
    <link:label id="lab_mrk_DeferredTaxAssetsUnrecognizedTaxBenefits_74ff2ab6-4273-4f8c-b1ce-18107aec9299_terseLabel_en-US" xlink:label="lab_mrk_DeferredTaxAssetsUnrecognizedTaxBenefits" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Unrecognized tax benefits, Assets</link:label>
    <link:label id="lab_mrk_DeferredTaxAssetsUnrecognizedTaxBenefits_label_en-US" xlink:label="lab_mrk_DeferredTaxAssetsUnrecognizedTaxBenefits" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Deferred Tax Assets Unrecognized Tax Benefits</link:label>
    <link:label id="lab_mrk_DeferredTaxAssetsUnrecognizedTaxBenefits_documentation_en-US" xlink:label="lab_mrk_DeferredTaxAssetsUnrecognizedTaxBenefits" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Deferred tax assets unrecognized tax benefits.</link:label>
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    <link:label id="lab_dei_EntityPublicFloat_cb13e7a4-252d-43cf-a4b3-409c4aa07d3d_terseLabel_en-US" xlink:label="lab_dei_EntityPublicFloat" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Entity Public Float</link:label>
    <link:label id="lab_dei_EntityPublicFloat_label_en-US" xlink:label="lab_dei_EntityPublicFloat" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Entity Public Float</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityPublicFloat" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityPublicFloat"/>
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    <link:label id="lab_mrk_RevenueRecognitionGoodsGoodsReturnPeriodPriortoExpirationDate_709e4a83-550a-4159-9e43-c05fccf7fe52_terseLabel_en-US" xlink:label="lab_mrk_RevenueRecognitionGoodsGoodsReturnPeriodPriortoExpirationDate" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Product return period</link:label>
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    <link:label id="lab_mrk_RevenueRecognitionGoodsGoodsReturnPeriodPriortoExpirationDate_documentation_en-US" xlink:label="lab_mrk_RevenueRecognitionGoodsGoodsReturnPeriodPriortoExpirationDate" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Revenue Recognition, Goods, Goods Return Period Prior to Expiration Date</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_mrk_RevenueRecognitionGoodsGoodsReturnPeriodPriortoExpirationDate" xlink:href="mrk-20201231.xsd#mrk_RevenueRecognitionGoodsGoodsReturnPeriodPriortoExpirationDate"/>
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    <link:label id="lab_us-gaap_BusinessCombinationsPolicy_4c94ca07-5c38-46d2-9eb2-816156e8d792_terseLabel_en-US" xlink:label="lab_us-gaap_BusinessCombinationsPolicy" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Acquisitions</link:label>
    <link:label id="lab_us-gaap_BusinessCombinationsPolicy_label_en-US" xlink:label="lab_us-gaap_BusinessCombinationsPolicy" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Business Combinations Policy [Policy Text Block]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationsPolicy" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessCombinationsPolicy"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_BusinessCombinationsPolicy" xlink:to="lab_us-gaap_BusinessCombinationsPolicy" xlink:type="arc" order="1"/>
    <link:label id="lab_mrk_PaymentsToAcquireBusinessFiveNetOfCashAcquired_b00b3cad-f11c-49c6-b27e-29d55fb63467_negatedTerseLabel_en-US" xlink:label="lab_mrk_PaymentsToAcquireBusinessFiveNetOfCashAcquired" xlink:role="http://www.xbrl.org/2009/role/negatedTerseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Acquisition of Peloton Therapeutics, Inc., net of cash acquired</link:label>
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    <link:label id="lab_mrk_PaymentsToAcquireBusinessFiveNetOfCashAcquired_documentation_en-US" xlink:label="lab_mrk_PaymentsToAcquireBusinessFiveNetOfCashAcquired" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Payments to Acquire Business Five, Net of Cash Acquired</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_mrk_PaymentsToAcquireBusinessFiveNetOfCashAcquired" xlink:href="mrk-20201231.xsd#mrk_PaymentsToAcquireBusinessFiveNetOfCashAcquired"/>
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    <link:label id="lab_dei_DocumentType_90a645fd-9c35-4541-9a03-7596b18d950d_terseLabel_en-US" xlink:label="lab_dei_DocumentType" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Document Type</link:label>
    <link:label id="lab_dei_DocumentType_label_en-US" xlink:label="lab_dei_DocumentType" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Document Type</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentType" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_DocumentType"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_dei_DocumentType" xlink:to="lab_dei_DocumentType" xlink:type="arc" order="1"/>
    <link:label id="lab_dei_IcfrAuditorAttestationFlag_cf63aa59-2a73-4b60-be47-37fbeb1b6f28_terseLabel_en-US" xlink:label="lab_dei_IcfrAuditorAttestationFlag" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">ICFR Auditor Attestation Flag</link:label>
    <link:label id="lab_dei_IcfrAuditorAttestationFlag_label_en-US" xlink:label="lab_dei_IcfrAuditorAttestationFlag" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">ICFR Auditor Attestation Flag</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_dei_IcfrAuditorAttestationFlag" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_IcfrAuditorAttestationFlag"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_dei_IcfrAuditorAttestationFlag" xlink:to="lab_dei_IcfrAuditorAttestationFlag" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_OtherNonoperatingIncomeExpense_ee73b11e-b3b4-4455-ae9c-d8e3cc52e767_negatedLabel_en-US" xlink:label="lab_us-gaap_OtherNonoperatingIncomeExpense" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Other (income) expense, net</link:label>
    <link:label id="lab_us-gaap_OtherNonoperatingIncomeExpense_c45d4012-4aab-4c2b-b6d6-54ef2c2ee844_negatedTotalLabel_en-US" xlink:label="lab_us-gaap_OtherNonoperatingIncomeExpense" xlink:role="http://www.xbrl.org/2009/role/negatedTotalLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Other (income) expense, net</link:label>
    <link:label id="lab_us-gaap_OtherNonoperatingIncomeExpense_label_en-US" xlink:label="lab_us-gaap_OtherNonoperatingIncomeExpense" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Other Nonoperating Income (Expense)</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpense" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherNonoperatingIncomeExpense"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_OtherNonoperatingIncomeExpense" xlink:to="lab_us-gaap_OtherNonoperatingIncomeExpense" xlink:type="arc" order="1"/>
    <link:label id="lab_mrk_McKessonCorporationAmerisourceBergenCorporationandCardinalHealthInc.Member_c171ed6b-71e4-40e1-8b99-bae7458ec574_terseLabel_en-US" xlink:label="lab_mrk_McKessonCorporationAmerisourceBergenCorporationandCardinalHealthInc.Member" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">McKesson Corporation, AmerisourceBergen Corporation and Cardinal Health, Inc.</link:label>
    <link:label id="lab_mrk_McKessonCorporationAmerisourceBergenCorporationandCardinalHealthInc.Member_label_en-US" xlink:label="lab_mrk_McKessonCorporationAmerisourceBergenCorporationandCardinalHealthInc.Member" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">McKesson Corporation, AmerisourceBergen Corporation and Cardinal Health, Inc. [Member]</link:label>
    <link:label id="lab_mrk_McKessonCorporationAmerisourceBergenCorporationandCardinalHealthInc.Member_documentation_en-US" xlink:label="lab_mrk_McKessonCorporationAmerisourceBergenCorporationandCardinalHealthInc.Member" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">McKesson Corporation, AmerisourceBergen Corporation and Cardinal Health, Inc. [Member]</link:label>
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    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_mrk_McKessonCorporationAmerisourceBergenCorporationandCardinalHealthInc.Member" xlink:to="lab_mrk_McKessonCorporationAmerisourceBergenCorporationandCardinalHealthInc.Member" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_TreasuryStockMember_948d582e-ef9f-4f54-a462-1ce0156d5f4e_terseLabel_en-US" xlink:label="lab_us-gaap_TreasuryStockMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Treasury Stock</link:label>
    <link:label id="lab_us-gaap_TreasuryStockMember_label_en-US" xlink:label="lab_us-gaap_TreasuryStockMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Treasury Stock [Member]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockMember" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_TreasuryStockMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_TreasuryStockMember" xlink:to="lab_us-gaap_TreasuryStockMember" xlink:type="arc" order="1"/>
    <link:label id="lab_mrk_ImplanonNexplanonMember_6d93dfe6-4c7d-4bf5-ac76-7d49e8f2b806_terseLabel_en-US" xlink:label="lab_mrk_ImplanonNexplanonMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Implanon/Nexplanon</link:label>
    <link:label id="lab_mrk_ImplanonNexplanonMember_label_en-US" xlink:label="lab_mrk_ImplanonNexplanonMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Implanon/Nexplanon [Member]</link:label>
    <link:label id="lab_mrk_ImplanonNexplanonMember_documentation_en-US" xlink:label="lab_mrk_ImplanonNexplanonMember" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Implanon/Nexplanon [Member].</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_mrk_ImplanonNexplanonMember" xlink:href="mrk-20201231.xsd#mrk_ImplanonNexplanonMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_mrk_ImplanonNexplanonMember" xlink:to="lab_mrk_ImplanonNexplanonMember" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_StatementBusinessSegmentsAxis_cb9b8e90-5359-41f9-b3c9-84631efbf874_terseLabel_en-US" xlink:label="lab_us-gaap_StatementBusinessSegmentsAxis" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Segments [Axis]</link:label>
    <link:label id="lab_us-gaap_StatementBusinessSegmentsAxis_label_en-US" xlink:label="lab_us-gaap_StatementBusinessSegmentsAxis" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Segments [Axis]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis" xlink:to="lab_us-gaap_StatementBusinessSegmentsAxis" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_PensionAndOtherPostretirementBenefitsDisclosureTextBlock_ca50d481-c7be-4084-a8d9-e9c406e48807_terseLabel_en-US" xlink:label="lab_us-gaap_PensionAndOtherPostretirementBenefitsDisclosureTextBlock" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Pension and Other Postretirement Benefit Plans</link:label>
    <link:label id="lab_us-gaap_PensionAndOtherPostretirementBenefitsDisclosureTextBlock_label_en-US" xlink:label="lab_us-gaap_PensionAndOtherPostretirementBenefitsDisclosureTextBlock" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Retirement Benefits [Text Block]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PensionAndOtherPostretirementBenefitsDisclosureTextBlock" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PensionAndOtherPostretirementBenefitsDisclosureTextBlock"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_PensionAndOtherPostretirementBenefitsDisclosureTextBlock" xlink:to="lab_us-gaap_PensionAndOtherPostretirementBenefitsDisclosureTextBlock" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_ValuationAllowancesAndReservesDomain_9f16c0c4-b3fe-4fc2-8c38-3e2be65c29ad_terseLabel_en-US" xlink:label="lab_us-gaap_ValuationAllowancesAndReservesDomain" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">SEC Schedule, 12-09, Valuation Allowances and Reserves [Domain]</link:label>
    <link:label id="lab_us-gaap_ValuationAllowancesAndReservesDomain_label_en-US" xlink:label="lab_us-gaap_ValuationAllowancesAndReservesDomain" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">SEC Schedule, 12-09, Valuation Allowances and Reserves [Domain]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationAllowancesAndReservesDomain" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ValuationAllowancesAndReservesDomain"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ValuationAllowancesAndReservesDomain" xlink:to="lab_us-gaap_ValuationAllowancesAndReservesDomain" xlink:type="arc" order="1"/>
    <link:label id="lab_mrk_CollaborativeArrangementsAbstract_f33466df-de93-470f-a310-dc8159dcc1a7_terseLabel_en-US" xlink:label="lab_mrk_CollaborativeArrangementsAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Collaborative Arrangements [Abstract]</link:label>
    <link:label id="lab_mrk_CollaborativeArrangementsAbstract_label_en-US" xlink:label="lab_mrk_CollaborativeArrangementsAbstract" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Collaborative Arrangements [Abstract]</link:label>
    <link:label id="lab_mrk_CollaborativeArrangementsAbstract_documentation_en-US" xlink:label="lab_mrk_CollaborativeArrangementsAbstract" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Collaborative Arrangements [Abstract]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_mrk_CollaborativeArrangementsAbstract" xlink:href="mrk-20201231.xsd#mrk_CollaborativeArrangementsAbstract"/>
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    <link:label id="lab_us-gaap_OtherCurrentAssetsMember_9ea73136-e33c-4e4f-b668-babb8e296eb4_terseLabel_en-US" xlink:label="lab_us-gaap_OtherCurrentAssetsMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Other current assets</link:label>
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    <link:label id="lab_us-gaap_DerivativeAssets_f9856513-dc85-435b-b542-5de4a6ef7919_verboseLabel_en-US" xlink:label="lab_us-gaap_DerivativeAssets" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Fair Value of Derivative, Asset</link:label>
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    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_DerivativeCollateralObligationToReturnCash" xlink:to="lab_us-gaap_DerivativeCollateralObligationToReturnCash" xlink:type="arc" order="1"/>
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    <link:label id="lab_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_c6c7c107-e941-4fc6-bf8f-eb57e3c10648_terseLabel_en-US" xlink:label="lab_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Schedule of Business Acquisitions, by Acquisition [Table]</link:label>
    <link:label id="lab_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_label_en-US" xlink:label="lab_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Schedule of Business Acquisitions, by Acquisition [Table]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
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    <link:label id="lab_us-gaap_PaymentsForRepurchaseOfCommonStock_ef089d35-3ab7-48d3-b50f-2b5db452b077_negatedLabel_en-US" xlink:label="lab_us-gaap_PaymentsForRepurchaseOfCommonStock" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Purchases of treasury stock</link:label>
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    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForRepurchaseOfCommonStock" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PaymentsForRepurchaseOfCommonStock"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_PaymentsForRepurchaseOfCommonStock" xlink:to="lab_us-gaap_PaymentsForRepurchaseOfCommonStock" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_4a6a24ed-3b60-42ad-b381-ee6914b3e89f_terseLabel_en-US" xlink:label="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Contractual term of options</link:label>
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    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1" xlink:to="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueAfterYearFive_709fb8c9-79bf-4bd0-a2fa-0f16d4fa2b98_terseLabel_en-US" xlink:label="lab_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueAfterYearFive" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Thereafter</link:label>
    <link:label id="lab_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueAfterYearFive_label_en-US" xlink:label="lab_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueAfterYearFive" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Lessee, Operating Lease, Liability, to be Paid, after Year Five</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueAfterYearFive" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueAfterYearFive"/>
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    <link:label id="lab_mrk_BayerAGMember_7c73b811-7ca9-4b42-ade6-4e171f6e4ddb_terseLabel_en-US" xlink:label="lab_mrk_BayerAGMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Bayer AG</link:label>
    <link:label id="lab_mrk_BayerAGMember_label_en-US" xlink:label="lab_mrk_BayerAGMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Bayer AG [Member]</link:label>
    <link:label id="lab_mrk_BayerAGMember_documentation_en-US" xlink:label="lab_mrk_BayerAGMember" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Bayer AG [Member]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_mrk_BayerAGMember" xlink:href="mrk-20201231.xsd#mrk_BayerAGMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_mrk_BayerAGMember" xlink:to="lab_mrk_BayerAGMember" xlink:type="arc" order="1"/>
    <link:label id="lab_dei_EntityAddressStateOrProvince_22a8306e-534c-4252-86db-ca2cbd610cba_terseLabel_en-US" xlink:label="lab_dei_EntityAddressStateOrProvince" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Entity Address, State or Province</link:label>
    <link:label id="lab_dei_EntityAddressStateOrProvince_label_en-US" xlink:label="lab_dei_EntityAddressStateOrProvince" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Entity Address, State or Province</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressStateOrProvince" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityAddressStateOrProvince"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_dei_EntityAddressStateOrProvince" xlink:to="lab_dei_EntityAddressStateOrProvince" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_8d64cb08-b7b2-4603-8944-050b83163e6d_negatedLabel_en-US" xlink:label="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Number of Shares, Vested</link:label>
    <link:label id="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_label_en-US" xlink:label="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod" xlink:to="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalStatutoryIncomeTaxRate_19ad4e92-8cb8-4433-bea5-022c67540831_terseLabel_en-US" xlink:label="lab_us-gaap_IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalStatutoryIncomeTaxRate" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">U.S. statutory rate applied to income before taxes</link:label>
    <link:label id="lab_us-gaap_IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalStatutoryIncomeTaxRate_label_en-US" xlink:label="lab_us-gaap_IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalStatutoryIncomeTaxRate" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Effective Income Tax Rate Reconciliation at Federal Statutory Income Tax Rate, Amount</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalStatutoryIncomeTaxRate" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalStatutoryIncomeTaxRate"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalStatutoryIncomeTaxRate" xlink:to="lab_us-gaap_IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalStatutoryIncomeTaxRate" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_AccountsPayableCurrent_58715a1a-df6c-488e-9c6e-4d16b60c49a9_terseLabel_en-US" xlink:label="lab_us-gaap_AccountsPayableCurrent" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Trade accounts payable</link:label>
    <link:label id="lab_us-gaap_AccountsPayableCurrent_label_en-US" xlink:label="lab_us-gaap_AccountsPayableCurrent" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Accounts Payable, Current</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsPayableCurrent" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AccountsPayableCurrent"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_AccountsPayableCurrent" xlink:to="lab_us-gaap_AccountsPayableCurrent" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_InternalUseSoftwarePolicy_9dd87732-8e08-4399-82e9-35758a770a92_terseLabel_en-US" xlink:label="lab_us-gaap_InternalUseSoftwarePolicy" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Software Capitalization</link:label>
    <link:label id="lab_us-gaap_InternalUseSoftwarePolicy_label_en-US" xlink:label="lab_us-gaap_InternalUseSoftwarePolicy" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Internal Use Software, Policy [Policy Text Block]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InternalUseSoftwarePolicy" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_InternalUseSoftwarePolicy"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_InternalUseSoftwarePolicy" xlink:to="lab_us-gaap_InternalUseSoftwarePolicy" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_RetainedEarningsAccumulatedDeficit_c2fc7973-09af-42c0-989e-2e2d42e63027_terseLabel_en-US" xlink:label="lab_us-gaap_RetainedEarningsAccumulatedDeficit" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Retained earnings</link:label>
    <link:label id="lab_us-gaap_RetainedEarningsAccumulatedDeficit_label_en-US" xlink:label="lab_us-gaap_RetainedEarningsAccumulatedDeficit" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Retained Earnings (Accumulated Deficit)</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsAccumulatedDeficit" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RetainedEarningsAccumulatedDeficit"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_RetainedEarningsAccumulatedDeficit" xlink:to="lab_us-gaap_RetainedEarningsAccumulatedDeficit" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_OperatingLeaseRightOfUseAsset_feae2006-6dc2-48f1-bdbc-2fe12e46b555_verboseLabel_en-US" xlink:label="lab_us-gaap_OperatingLeaseRightOfUseAsset" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Other assets</link:label>
    <link:label id="lab_us-gaap_OperatingLeaseRightOfUseAsset_label_en-US" xlink:label="lab_us-gaap_OperatingLeaseRightOfUseAsset" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Operating Lease, Right-of-Use Asset</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseRightOfUseAsset" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OperatingLeaseRightOfUseAsset"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_OperatingLeaseRightOfUseAsset" xlink:to="lab_us-gaap_OperatingLeaseRightOfUseAsset" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_AccountingStandardsUpdate201601Member_d5b4ddfd-45ec-4871-8409-af29ddc8b7ba_terseLabel_en-US" xlink:label="lab_us-gaap_AccountingStandardsUpdate201601Member" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Accounting Standards Update 2016-01</link:label>
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    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_AccountingStandardsUpdate201601Member" xlink:to="lab_us-gaap_AccountingStandardsUpdate201601Member" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_DeferredTaxLiabilitiesPropertyPlantAndEquipment_16537566-c3ef-4f58-a418-2d9f27ce1ddb_terseLabel_en-US" xlink:label="lab_us-gaap_DeferredTaxLiabilitiesPropertyPlantAndEquipment" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Accelerated depreciation, Liabilities</link:label>
    <link:label id="lab_us-gaap_DeferredTaxLiabilitiesPropertyPlantAndEquipment_label_en-US" xlink:label="lab_us-gaap_DeferredTaxLiabilitiesPropertyPlantAndEquipment" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Deferred Tax Liabilities, Property, Plant and Equipment</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredTaxLiabilitiesPropertyPlantAndEquipment" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DeferredTaxLiabilitiesPropertyPlantAndEquipment"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_DeferredTaxLiabilitiesPropertyPlantAndEquipment" xlink:to="lab_us-gaap_DeferredTaxLiabilitiesPropertyPlantAndEquipment" xlink:type="arc" order="1"/>
    <link:label id="lab_mrk_ArQuleMember_88dc0330-6201-4f31-9280-d14509377c83_terseLabel_en-US" xlink:label="lab_mrk_ArQuleMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">ArQule</link:label>
    <link:label id="lab_mrk_ArQuleMember_label_en-US" xlink:label="lab_mrk_ArQuleMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">ArQule [Member]</link:label>
    <link:label id="lab_mrk_ArQuleMember_documentation_en-US" xlink:label="lab_mrk_ArQuleMember" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">ArQule [Member]</link:label>
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    <link:label id="lab_us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_e9fe7180-c247-4222-b12d-7a1621472fab_terseLabel_en-US" xlink:label="lab_us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Debt securities, amortized cost</link:label>
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    <link:label id="lab_us-gaap_StatementOfCashFlowsAbstract_0b366698-88c1-42b0-b80c-9909d47d9412_terseLabel_en-US" xlink:label="lab_us-gaap_StatementOfCashFlowsAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Statement of Cash Flows [Abstract]</link:label>
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    <link:label id="lab_mrk_A1.875Notesdue2026Member_documentation_en-US" xlink:label="lab_mrk_A1.875Notesdue2026Member" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">1.875% Notes due 2026 [Member]</link:label>
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    <link:label id="lab_mrk_SingulairMember_ed33b174-ed2d-4e14-afdf-4bd774543fec_terseLabel_en-US" xlink:label="lab_mrk_SingulairMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Singulair</link:label>
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    <link:label id="lab_us-gaap_OtherRestructuringMember_550e805d-2a0f-4530-ac24-78d46b8f17bc_terseLabel_en-US" xlink:label="lab_us-gaap_OtherRestructuringMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Other</link:label>
    <link:label id="lab_us-gaap_OtherRestructuringMember_label_en-US" xlink:label="lab_us-gaap_OtherRestructuringMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Other Restructuring [Member]</link:label>
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    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_OtherRestructuringMember" xlink:to="lab_us-gaap_OtherRestructuringMember" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_NonUsMember_14ff4fff-0314-4857-8861-b65c008b85e6_terseLabel_en-US" xlink:label="lab_us-gaap_NonUsMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Outside of the United States</link:label>
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    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_NonUsMember" xlink:to="lab_us-gaap_NonUsMember" xlink:type="arc" order="1"/>
    <link:label id="lab_mrk_ZepatierMember_aeb7d7ee-5d6d-4008-82e2-82b1a72b35f1_terseLabel_en-US" xlink:label="lab_mrk_ZepatierMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Zepatier</link:label>
    <link:label id="lab_mrk_ZepatierMember_label_en-US" xlink:label="lab_mrk_ZepatierMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Zepatier [Member]</link:label>
    <link:label id="lab_mrk_ZepatierMember_documentation_en-US" xlink:label="lab_mrk_ZepatierMember" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Zepatier [Member]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_mrk_ZepatierMember" xlink:href="mrk-20201231.xsd#mrk_ZepatierMember"/>
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    <link:label id="lab_us-gaap_AcceleratedShareRepurchasesDateAxis_5f753f36-0432-449e-af2f-32417c7ac8bc_terseLabel_en-US" xlink:label="lab_us-gaap_AcceleratedShareRepurchasesDateAxis" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Accelerated Share Repurchases, Date [Axis]</link:label>
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    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AcceleratedShareRepurchasesDateAxis" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AcceleratedShareRepurchasesDateAxis"/>
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    <link:label id="lab_mrk_LossContingencyClaimsonAppealNumber_3eb84c87-7f15-49bc-ac44-bcc3ee4f74c3_terseLabel_en-US" xlink:label="lab_mrk_LossContingencyClaimsonAppealNumber" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Loss contingency, claims on appeal, number</link:label>
    <link:label id="lab_mrk_LossContingencyClaimsonAppealNumber_label_en-US" xlink:label="lab_mrk_LossContingencyClaimsonAppealNumber" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Loss Contingency, Claims on Appeal, Number</link:label>
    <link:label id="lab_mrk_LossContingencyClaimsonAppealNumber_documentation_en-US" xlink:label="lab_mrk_LossContingencyClaimsonAppealNumber" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Loss Contingency, Claims on Appeal, Number</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_mrk_LossContingencyClaimsonAppealNumber" xlink:href="mrk-20201231.xsd#mrk_LossContingencyClaimsonAppealNumber"/>
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    <link:label id="lab_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo_bbd50dae-8d69-4d7b-9346-fe836e4746d9_terseLabel_en-US" xlink:label="lab_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Long-term debt, maturities, repayments of principal in 2022</link:label>
    <link:label id="lab_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo_label_en-US" xlink:label="lab_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Long-Term Debt, Maturity, Year Two</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo"/>
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    <link:label id="lab_mrk_A2.45notesdue2050Member_dd77591e-40a1-47f2-b2f5-30ca4a0135c8_terseLabel_en-US" xlink:label="lab_mrk_A2.45notesdue2050Member" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">2.45% notes due 2050</link:label>
    <link:label id="lab_mrk_A2.45notesdue2050Member_label_en-US" xlink:label="lab_mrk_A2.45notesdue2050Member" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">2.45% notes due 2050 [Member]</link:label>
    <link:label id="lab_mrk_A2.45notesdue2050Member_documentation_en-US" xlink:label="lab_mrk_A2.45notesdue2050Member" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">2.45% notes due 2050 [Member]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_mrk_A2.45notesdue2050Member" xlink:href="mrk-20201231.xsd#mrk_A2.45notesdue2050Member"/>
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    <link:label id="lab_us-gaap_SiteContingencyTable_f4f57e91-9770-4daa-879f-646441b5cf31_terseLabel_en-US" xlink:label="lab_us-gaap_SiteContingencyTable" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Site Contingency [Table]</link:label>
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    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_SiteContingencyTable" xlink:to="lab_us-gaap_SiteContingencyTable" xlink:type="arc" order="1"/>
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    <link:label id="lab_us-gaap_DerivativeAssetNotOffsetPolicyElectionDeduction_bd2b1255-c680-49c8-82fa-9b6e36e2083b_negatedLabel_en-US" xlink:label="lab_us-gaap_DerivativeAssetNotOffsetPolicyElectionDeduction" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Gross amount subject to offset in master netting arrangements not offset in the consolidated balance sheet, Asset</link:label>
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    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_DerivativeAssetNotOffsetPolicyElectionDeduction" xlink:to="lab_us-gaap_DerivativeAssetNotOffsetPolicyElectionDeduction" xlink:type="arc" order="1"/>
    <link:label id="lab_mrk_ImmuneDesignMember_66f0ae87-a593-408c-9dcd-59c30da76084_terseLabel_en-US" xlink:label="lab_mrk_ImmuneDesignMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Immune Design</link:label>
    <link:label id="lab_mrk_ImmuneDesignMember_label_en-US" xlink:label="lab_mrk_ImmuneDesignMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Immune Design [Member]</link:label>
    <link:label id="lab_mrk_ImmuneDesignMember_documentation_en-US" xlink:label="lab_mrk_ImmuneDesignMember" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Immune Design [Member]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_mrk_ImmuneDesignMember" xlink:href="mrk-20201231.xsd#mrk_ImmuneDesignMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_mrk_ImmuneDesignMember" xlink:to="lab_mrk_ImmuneDesignMember" xlink:type="arc" order="1"/>
    <link:label id="lab_mrk_COVID19Member_d4a80b98-eb89-40bb-954c-3540958b7a55_terseLabel_en-US" xlink:label="lab_mrk_COVID19Member" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">COVID-19</link:label>
    <link:label id="lab_mrk_COVID19Member_label_en-US" xlink:label="lab_mrk_COVID19Member" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">COVID-19 [Member]</link:label>
    <link:label id="lab_mrk_COVID19Member_documentation_en-US" xlink:label="lab_mrk_COVID19Member" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">COVID-19</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_mrk_COVID19Member" xlink:href="mrk-20201231.xsd#mrk_COVID19Member"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_mrk_COVID19Member" xlink:to="lab_mrk_COVID19Member" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_DebtInstrumentAxis_ae94852e-116b-4808-a226-2bc2d16a5e7d_terseLabel_en-US" xlink:label="lab_us-gaap_DebtInstrumentAxis" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Debt Instrument [Axis]</link:label>
    <link:label id="lab_us-gaap_DebtInstrumentAxis_label_en-US" xlink:label="lab_us-gaap_DebtInstrumentAxis" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Debt Instrument [Axis]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_DebtInstrumentAxis" xlink:to="lab_us-gaap_DebtInstrumentAxis" xlink:type="arc" order="1"/>
    <link:label id="lab_mrk_AtozetMember_f5286f79-514a-4970-b39b-55d79ea2dce2_terseLabel_en-US" xlink:label="lab_mrk_AtozetMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Atozet</link:label>
    <link:label id="lab_mrk_AtozetMember_label_en-US" xlink:label="lab_mrk_AtozetMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Atozet [Member]</link:label>
    <link:label id="lab_mrk_AtozetMember_documentation_en-US" xlink:label="lab_mrk_AtozetMember" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Atozet [Member]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_mrk_AtozetMember" xlink:href="mrk-20201231.xsd#mrk_AtozetMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_mrk_AtozetMember" xlink:to="lab_mrk_AtozetMember" xlink:type="arc" order="1"/>
    <link:label id="lab_mrk_EffectiveIncomeTaxRateReconciliationBusinessCombination_ff283721-65f6-4342-8284-09c9bad35951_terseLabel_en-US" xlink:label="lab_mrk_EffectiveIncomeTaxRateReconciliationBusinessCombination" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Acquisition of Peloton</link:label>
    <link:label id="lab_mrk_EffectiveIncomeTaxRateReconciliationBusinessCombination_label_en-US" xlink:label="lab_mrk_EffectiveIncomeTaxRateReconciliationBusinessCombination" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Effective Income Tax Rate Reconciliation, Business Combination</link:label>
    <link:label id="lab_mrk_EffectiveIncomeTaxRateReconciliationBusinessCombination_documentation_en-US" xlink:label="lab_mrk_EffectiveIncomeTaxRateReconciliationBusinessCombination" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Effective Income Tax Rate Reconciliation, Business Combination</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_mrk_EffectiveIncomeTaxRateReconciliationBusinessCombination" xlink:href="mrk-20201231.xsd#mrk_EffectiveIncomeTaxRateReconciliationBusinessCombination"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_mrk_EffectiveIncomeTaxRateReconciliationBusinessCombination" xlink:to="lab_mrk_EffectiveIncomeTaxRateReconciliationBusinessCombination" xlink:type="arc" order="1"/>
    <link:label id="lab_mrk_InventoryTable_72528eb5-3304-4ce1-b27b-13e96a282a13_terseLabel_en-US" xlink:label="lab_mrk_InventoryTable" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Inventory [Table]</link:label>
    <link:label id="lab_mrk_InventoryTable_label_en-US" xlink:label="lab_mrk_InventoryTable" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Inventory [Table]</link:label>
    <link:label id="lab_mrk_InventoryTable_documentation_en-US" xlink:label="lab_mrk_InventoryTable" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Inventory [Table]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_mrk_InventoryTable" xlink:href="mrk-20201231.xsd#mrk_InventoryTable"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_mrk_InventoryTable" xlink:to="lab_mrk_InventoryTable" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_OperatingSegmentsMember_748c448b-6f49-40c8-a7d4-b631ab9632cb_terseLabel_en-US" xlink:label="lab_us-gaap_OperatingSegmentsMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Operating Segments</link:label>
    <link:label id="lab_us-gaap_OperatingSegmentsMember_dd487bc9-7e07-4886-aca7-edc1d59f12f8_verboseLabel_en-US" xlink:label="lab_us-gaap_OperatingSegmentsMember" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Total segment profits</link:label>
    <link:label id="lab_us-gaap_OperatingSegmentsMember_label_en-US" xlink:label="lab_us-gaap_OperatingSegmentsMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Operating Segments [Member]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OperatingSegmentsMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_OperatingSegmentsMember" xlink:to="lab_us-gaap_OperatingSegmentsMember" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_ContingentConsiderationByTypeAxis_586c7711-4c0e-4515-b5f5-6db18a277c8d_terseLabel_en-US" xlink:label="lab_us-gaap_ContingentConsiderationByTypeAxis" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Contingent Consideration by Type [Axis]</link:label>
    <link:label id="lab_us-gaap_ContingentConsiderationByTypeAxis_label_en-US" xlink:label="lab_us-gaap_ContingentConsiderationByTypeAxis" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Contingent Consideration by Type [Axis]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContingentConsiderationByTypeAxis" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ContingentConsiderationByTypeAxis"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ContingentConsiderationByTypeAxis" xlink:to="lab_us-gaap_ContingentConsiderationByTypeAxis" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_ClassOfStockLineItems_3f70a92d-abcd-4eb4-811d-6a3012417ca1_terseLabel_en-US" xlink:label="lab_us-gaap_ClassOfStockLineItems" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Class of Stock [Line Items]</link:label>
    <link:label id="lab_us-gaap_ClassOfStockLineItems_label_en-US" xlink:label="lab_us-gaap_ClassOfStockLineItems" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Class of Stock [Line Items]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockLineItems" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ClassOfStockLineItems"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ClassOfStockLineItems" xlink:to="lab_us-gaap_ClassOfStockLineItems" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_IncreaseDecreaseInAccruedLiabilities_74d86503-a2c5-42bf-b7f8-5de9588d0fa4_terseLabel_en-US" xlink:label="lab_us-gaap_IncreaseDecreaseInAccruedLiabilities" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Accrued and other current liabilities</link:label>
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    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInAccruedLiabilities" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IncreaseDecreaseInAccruedLiabilities"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_IncreaseDecreaseInAccruedLiabilities" xlink:to="lab_us-gaap_IncreaseDecreaseInAccruedLiabilities" xlink:type="arc" order="1"/>
    <link:label id="lab_mrk_DefinedBenefitPlanOtherChangesPlanAssets_d9489271-ee0d-44f8-8409-00b3da8405b9_terseLabel_en-US" xlink:label="lab_mrk_DefinedBenefitPlanOtherChangesPlanAssets" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Other</link:label>
    <link:label id="lab_mrk_DefinedBenefitPlanOtherChangesPlanAssets_label_en-US" xlink:label="lab_mrk_DefinedBenefitPlanOtherChangesPlanAssets" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Defined Benefit Plan Other Changes Plan Assets</link:label>
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    <link:loc xlink:type="locator" xlink:label="loc_mrk_DefinedBenefitPlanOtherChangesPlanAssets" xlink:href="mrk-20201231.xsd#mrk_DefinedBenefitPlanOtherChangesPlanAssets"/>
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    <link:label id="lab_us-gaap_TreasuryStockValueAcquiredCostMethod_2d94c93a-0b6f-41fe-8bcd-3de5b32ecd97_negatedLabel_en-US" xlink:label="lab_us-gaap_TreasuryStockValueAcquiredCostMethod" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Treasury stock shares purchased</link:label>
    <link:label id="lab_us-gaap_TreasuryStockValueAcquiredCostMethod_label_en-US" xlink:label="lab_us-gaap_TreasuryStockValueAcquiredCostMethod" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Treasury Stock, Value, Acquired, Cost Method</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockValueAcquiredCostMethod" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_TreasuryStockValueAcquiredCostMethod"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_TreasuryStockValueAcquiredCostMethod" xlink:to="lab_us-gaap_TreasuryStockValueAcquiredCostMethod" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_DerivativeLiabilities_3d7da584-5388-4e8d-83ad-4b1fb8dce680_verboseLabel_en-US" xlink:label="lab_us-gaap_DerivativeLiabilities" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Fair Value of Derivative, Liability</link:label>
    <link:label id="lab_us-gaap_DerivativeLiabilities_7967100b-4429-4bfb-a535-bfb866ee0b6b_terseLabel_en-US" xlink:label="lab_us-gaap_DerivativeLiabilities" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Gross amounts recognized in the consolidated balance sheet, Liability</link:label>
    <link:label id="lab_us-gaap_DerivativeLiabilities_2fc60809-8e51-478d-aa32-1351a088f2ae_netLabel_en-US" xlink:label="lab_us-gaap_DerivativeLiabilities" xlink:role="http://www.xbrl.org/2009/role/netLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Derivative liabilities</link:label>
    <link:label id="lab_us-gaap_DerivativeLiabilities_label_en-US" xlink:label="lab_us-gaap_DerivativeLiabilities" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Derivative Liability</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLiabilities" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DerivativeLiabilities"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_DerivativeLiabilities" xlink:to="lab_us-gaap_DerivativeLiabilities" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_b1963dce-111f-40a7-8f7c-241574d713bb_terseLabel_en-US" xlink:label="lab_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Adjustments to reconcile net income to net cash provided by operating activities:</link:label>
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    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="lab_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:type="arc" order="1"/>
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    <link:label id="lab_us-gaap_DeferredTaxAssetsInventory_b6242278-6c79-4492-b443-226065c6c1c3_terseLabel_en-US" xlink:label="lab_us-gaap_DeferredTaxAssetsInventory" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Inventory related, Assets</link:label>
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    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxReconciliationStateAndLocalIncomeTaxes" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IncomeTaxReconciliationStateAndLocalIncomeTaxes"/>
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    <link:label id="lab_mrk_RecognizedAsAbstract_1e3bb711-ade5-4623-bb40-36da47ba106d_terseLabel_en-US" xlink:label="lab_mrk_RecognizedAsAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Recognized as:</link:label>
    <link:label id="lab_mrk_RecognizedAsAbstract_label_en-US" xlink:label="lab_mrk_RecognizedAsAbstract" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Recognized As [Abstract]</link:label>
    <link:label id="lab_mrk_RecognizedAsAbstract_documentation_en-US" xlink:label="lab_mrk_RecognizedAsAbstract" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Recognized as.</link:label>
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    <link:label id="lab_mrk_AcceleratedShareRepurchaseAgreementMember_b9d25b57-4ca8-4c2e-bca2-4e2bfffb4cf0_terseLabel_en-US" xlink:label="lab_mrk_AcceleratedShareRepurchaseAgreementMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Accelerated Share Repurchase Agreement</link:label>
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    <link:label id="lab_us-gaap_LossContingenciesByNatureOfContingencyAxis_75c29ebe-a3d1-484b-8ee4-ae1eb0188d3a_terseLabel_en-US" xlink:label="lab_us-gaap_LossContingenciesByNatureOfContingencyAxis" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Loss Contingency Nature [Axis]</link:label>
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    <link:label id="lab_us-gaap_ResearchAndDevelopmentExpense_8a8bbbe0-d610-4251-9b61-9a1fc9f04926_terseLabel_en-US" xlink:label="lab_us-gaap_ResearchAndDevelopmentExpense" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Research and development</link:label>
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    <link:label id="lab_us-gaap_ResearchAndDevelopmentExpense_label_en-US" xlink:label="lab_us-gaap_ResearchAndDevelopmentExpense" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Research and Development Expense</link:label>
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    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ResearchAndDevelopmentExpense" xlink:to="lab_us-gaap_ResearchAndDevelopmentExpense" xlink:type="arc" order="1"/>
    <link:label id="lab_mrk_PrimaxinMember_6d8c392f-7942-4b34-9e35-accf0200bbba_terseLabel_en-US" xlink:label="lab_mrk_PrimaxinMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Primaxin</link:label>
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    <link:label id="lab_mrk_PrimaxinMember_documentation_en-US" xlink:label="lab_mrk_PrimaxinMember" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Primaxin [Member].</link:label>
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    <link:label id="lab_us-gaap_DefinedBenefitPlanPensionPlansWithAccumulatedBenefitObligationsInExcessOfPlanAssetsAggregateProjectedBenefitObligation_179cd49e-8693-4f43-849a-afb1ec6aa87e_terseLabel_en-US" xlink:label="lab_us-gaap_DefinedBenefitPlanPensionPlansWithAccumulatedBenefitObligationsInExcessOfPlanAssetsAggregateProjectedBenefitObligation" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Pension plans with a projected benefit obligation in excess of plan assets, projected benefit obligation</link:label>
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    <link:label id="lab_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesLongTermDebt_a05be6c7-8df5-4651-b368-6fe6d1bf537e_terseLabel_en-US" xlink:label="lab_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesLongTermDebt" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Debt assumed</link:label>
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    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_SubsequentEventMember" xlink:to="lab_us-gaap_SubsequentEventMember" xlink:type="arc" order="1"/>
    <link:label id="lab_mrk_UpfrontAndMilestonePaymentsMadeToCollaborativePartner_0dc119a2-d274-468c-9575-0095647d350d_terseLabel_en-US" xlink:label="lab_mrk_UpfrontAndMilestonePaymentsMadeToCollaborativePartner" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Upfront and milestone payments</link:label>
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    <link:label id="lab_us-gaap_DomesticCountryMember_a1570560-5be5-4116-a018-a8052d285cf1_terseLabel_en-US" xlink:label="lab_us-gaap_DomesticCountryMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Federal</link:label>
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    <link:label id="lab_us-gaap_PriorPeriodReclassificationAdjustmentDescription_1fd0752c-0317-4c01-a74c-b6e81ed60706_terseLabel_en-US" xlink:label="lab_us-gaap_PriorPeriodReclassificationAdjustmentDescription" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Reclassifications</link:label>
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    <link:label id="lab_mrk_LongTermDebtCurrentMaturitiesMember_f2972eb0-2d44-447e-99b9-7850996e9789_terseLabel_en-US" xlink:label="lab_mrk_LongTermDebtCurrentMaturitiesMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Loans payable and current portion of long-term debt</link:label>
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    <link:label id="lab_us-gaap_TradingSecurities_0a16e384-cb13-4050-ba79-4b7e8b5fff9b_totalLabel_en-US" xlink:label="lab_us-gaap_TradingSecurities" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Investments</link:label>
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    <link:label id="lab_us-gaap_NondesignatedMember_442b6227-43c2-49ba-a539-3af44a335762_terseLabel_en-US" xlink:label="lab_us-gaap_NondesignatedMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Derivatives Not Designated as Hedging Instruments</link:label>
    <link:label id="lab_us-gaap_NondesignatedMember_label_en-US" xlink:label="lab_us-gaap_NondesignatedMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Not Designated as Hedging Instrument [Member]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NondesignatedMember" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NondesignatedMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_NondesignatedMember" xlink:to="lab_us-gaap_NondesignatedMember" xlink:type="arc" order="1"/>
    <link:label id="lab_mrk_ChargeForFuturePaymentsRelatedToCollaborationLicenseOptions_b497ae8e-f63f-4144-ad51-ffa1bcbd11c7_terseLabel_en-US" xlink:label="lab_mrk_ChargeForFuturePaymentsRelatedToCollaborationLicenseOptions" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Charge for future payments related to collaboration license options</link:label>
    <link:label id="lab_mrk_ChargeForFuturePaymentsRelatedToCollaborationLicenseOptions_label_en-US" xlink:label="lab_mrk_ChargeForFuturePaymentsRelatedToCollaborationLicenseOptions" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Charge for future payments related to collaboration license options</link:label>
    <link:label id="lab_mrk_ChargeForFuturePaymentsRelatedToCollaborationLicenseOptions_documentation_en-US" xlink:label="lab_mrk_ChargeForFuturePaymentsRelatedToCollaborationLicenseOptions" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Charge for future payments related to collaboration license options</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_mrk_ChargeForFuturePaymentsRelatedToCollaborationLicenseOptions" xlink:href="mrk-20201231.xsd#mrk_ChargeForFuturePaymentsRelatedToCollaborationLicenseOptions"/>
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    <link:label id="lab_us-gaap_GoodwillImpairmentLoss_b40e321e-0cbc-4894-8a9f-d904633819fe_negatedTerseLabel_en-US" xlink:label="lab_us-gaap_GoodwillImpairmentLoss" xlink:role="http://www.xbrl.org/2009/role/negatedTerseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Impairments</link:label>
    <link:label id="lab_us-gaap_GoodwillImpairmentLoss_24c0b854-2047-48d6-9fad-be335c9d7d7f_terseLabel_en-US" xlink:label="lab_us-gaap_GoodwillImpairmentLoss" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Goodwill impairment charges</link:label>
    <link:label id="lab_us-gaap_GoodwillImpairmentLoss_label_en-US" xlink:label="lab_us-gaap_GoodwillImpairmentLoss" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Goodwill, Impairment Loss</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillImpairmentLoss" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_GoodwillImpairmentLoss"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_GoodwillImpairmentLoss" xlink:to="lab_us-gaap_GoodwillImpairmentLoss" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_AccountsReceivableNetCurrent_f395bfc4-494e-46f4-96a9-148702e3d95a_terseLabel_en-US" xlink:label="lab_us-gaap_AccountsReceivableNetCurrent" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Accounts receivable (net of allowance for doubtful accounts of $85 in 2020 and $86 in 2019)</link:label>
    <link:label id="lab_us-gaap_AccountsReceivableNetCurrent_label_en-US" xlink:label="lab_us-gaap_AccountsReceivableNetCurrent" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Accounts Receivable, after Allowance for Credit Loss, Current</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableNetCurrent" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AccountsReceivableNetCurrent"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_AccountsReceivableNetCurrent" xlink:to="lab_us-gaap_AccountsReceivableNetCurrent" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_AccumulatedOtherComprehensiveIncomeLossDefinedBenefitPensionAndOtherPostretirementPlansNetOfTax_f73ffbc7-b154-4b15-9605-56b291549c02_terseLabel_en-US" xlink:label="lab_us-gaap_AccumulatedOtherComprehensiveIncomeLossDefinedBenefitPensionAndOtherPostretirementPlansNetOfTax" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Pension and other postretirement benefit plans, net loss and prior service (credit) included in AOCI</link:label>
    <link:label id="lab_us-gaap_AccumulatedOtherComprehensiveIncomeLossDefinedBenefitPensionAndOtherPostretirementPlansNetOfTax_label_en-US" xlink:label="lab_us-gaap_AccumulatedOtherComprehensiveIncomeLossDefinedBenefitPensionAndOtherPostretirementPlansNetOfTax" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Accumulated Other Comprehensive (Income) Loss, Defined Benefit Plan, after Tax</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossDefinedBenefitPensionAndOtherPostretirementPlansNetOfTax" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossDefinedBenefitPensionAndOtherPostretirementPlansNetOfTax"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossDefinedBenefitPensionAndOtherPostretirementPlansNetOfTax" xlink:to="lab_us-gaap_AccumulatedOtherComprehensiveIncomeLossDefinedBenefitPensionAndOtherPostretirementPlansNetOfTax" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_InventoryFinishedGoods_6f8682b7-3774-4b05-abcc-ac195edf8f18_terseLabel_en-US" xlink:label="lab_us-gaap_InventoryFinishedGoods" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Finished goods</link:label>
    <link:label id="lab_us-gaap_InventoryFinishedGoods_label_en-US" xlink:label="lab_us-gaap_InventoryFinishedGoods" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Inventory, Finished Goods, Gross</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InventoryFinishedGoods" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_InventoryFinishedGoods"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_InventoryFinishedGoods" xlink:to="lab_us-gaap_InventoryFinishedGoods" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDue_186fd7c7-e765-4978-ad45-0510cdc63e45_totalLabel_en-US" xlink:label="lab_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDue" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Total lease payments</link:label>
    <link:label id="lab_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDue_label_en-US" xlink:label="lab_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDue" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Lessee, Operating Lease, Liability, to be Paid</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDue" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LesseeOperatingLeaseLiabilityPaymentsDue"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDue" xlink:to="lab_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDue" xlink:type="arc" order="1"/>
    <link:label id="lab_mrk_CollaborativeArrangementExpenses_b6a24c61-6cd4-4cb9-b90c-96f569a88acb_terseLabel_en-US" xlink:label="lab_mrk_CollaborativeArrangementExpenses" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Expenses</link:label>
    <link:label id="lab_mrk_CollaborativeArrangementExpenses_label_en-US" xlink:label="lab_mrk_CollaborativeArrangementExpenses" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Collaborative Arrangement, Expenses</link:label>
    <link:label id="lab_mrk_CollaborativeArrangementExpenses_documentation_en-US" xlink:label="lab_mrk_CollaborativeArrangementExpenses" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Collaborative Arrangement, Expenses</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_mrk_CollaborativeArrangementExpenses" xlink:href="mrk-20201231.xsd#mrk_CollaborativeArrangementExpenses"/>
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    <link:label id="lab_us-gaap_DeferredTaxAssetsOther_daf3a6be-08e9-4155-876d-18e21f20d311_terseLabel_en-US" xlink:label="lab_us-gaap_DeferredTaxAssetsOther" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Other, Assets</link:label>
    <link:label id="lab_us-gaap_DeferredTaxAssetsOther_label_en-US" xlink:label="lab_us-gaap_DeferredTaxAssetsOther" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Deferred Tax Assets, Other</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredTaxAssetsOther" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DeferredTaxAssetsOther"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_DeferredTaxAssetsOther" xlink:to="lab_us-gaap_DeferredTaxAssetsOther" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_EffectiveIncomeTaxRateReconciliationNondeductibleExpenseRestructuringCharges_184cb50f-f90e-40b4-bcba-baaa04b4c33f_terseLabel_en-US" xlink:label="lab_us-gaap_EffectiveIncomeTaxRateReconciliationNondeductibleExpenseRestructuringCharges" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Restructuring</link:label>
    <link:label id="lab_us-gaap_EffectiveIncomeTaxRateReconciliationNondeductibleExpenseRestructuringCharges_label_en-US" xlink:label="lab_us-gaap_EffectiveIncomeTaxRateReconciliationNondeductibleExpenseRestructuringCharges" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Effective Income Tax Rate Reconciliation, Nondeductible Expense, Restructuring Charges, Percent</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateReconciliationNondeductibleExpenseRestructuringCharges" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationNondeductibleExpenseRestructuringCharges"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_EffectiveIncomeTaxRateReconciliationNondeductibleExpenseRestructuringCharges" xlink:to="lab_us-gaap_EffectiveIncomeTaxRateReconciliationNondeductibleExpenseRestructuringCharges" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_ForeignPlanMember_adde819c-707e-429f-8c0a-a0d3bcb4c924_terseLabel_en-US" xlink:label="lab_us-gaap_ForeignPlanMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">International</link:label>
    <link:label id="lab_us-gaap_ForeignPlanMember_label_en-US" xlink:label="lab_us-gaap_ForeignPlanMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Foreign Plan [Member]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignPlanMember" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ForeignPlanMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ForeignPlanMember" xlink:to="lab_us-gaap_ForeignPlanMember" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_RestructuringChargesMember_f4fabba0-9bb6-4db8-a7e3-7bc7a05d3acb_terseLabel_en-US" xlink:label="lab_us-gaap_RestructuringChargesMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Restructuring costs</link:label>
    <link:label id="lab_us-gaap_RestructuringChargesMember_label_en-US" xlink:label="lab_us-gaap_RestructuringChargesMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Restructuring Charges [Member]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringChargesMember" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RestructuringChargesMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_RestructuringChargesMember" xlink:to="lab_us-gaap_RestructuringChargesMember" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostWeightedAverageInterestCreditingRate_7d4fb8ec-cdd9-4782-a6b4-b7e8fbd18fe5_terseLabel_en-US" xlink:label="lab_us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostWeightedAverageInterestCreditingRate" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Interest crediting rate</link:label>
    <link:label id="lab_us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostWeightedAverageInterestCreditingRate_label_en-US" xlink:label="lab_us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostWeightedAverageInterestCreditingRate" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Weighted-Average Interest Crediting Rate</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostWeightedAverageInterestCreditingRate" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostWeightedAverageInterestCreditingRate"/>
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    <link:label id="lab_mrk_DeferredTaxLiabilitiesPensionsAndOtherPostretirementBenefitPlans_0520b61b-3032-42db-af83-ce0a884f45c1_terseLabel_en-US" xlink:label="lab_mrk_DeferredTaxLiabilitiesPensionsAndOtherPostretirementBenefitPlans" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Pensions and other postretirement benefits, Liabilities</link:label>
    <link:label id="lab_mrk_DeferredTaxLiabilitiesPensionsAndOtherPostretirementBenefitPlans_label_en-US" xlink:label="lab_mrk_DeferredTaxLiabilitiesPensionsAndOtherPostretirementBenefitPlans" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Deferred Tax Liabilities Pensions And Other Postretirement Benefit Plans</link:label>
    <link:label id="lab_mrk_DeferredTaxLiabilitiesPensionsAndOtherPostretirementBenefitPlans_documentation_en-US" xlink:label="lab_mrk_DeferredTaxLiabilitiesPensionsAndOtherPostretirementBenefitPlans" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Amount of deferred tax liability attributable to taxable temporary differences from pensions and other postretirement benefits.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_mrk_DeferredTaxLiabilitiesPensionsAndOtherPostretirementBenefitPlans" xlink:href="mrk-20201231.xsd#mrk_DeferredTaxLiabilitiesPensionsAndOtherPostretirementBenefitPlans"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_mrk_DeferredTaxLiabilitiesPensionsAndOtherPostretirementBenefitPlans" xlink:to="lab_mrk_DeferredTaxLiabilitiesPensionsAndOtherPostretirementBenefitPlans" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_ForeignCurrencyTransactionsAndTranslationsPolicyTextBlock_5f1278ab-39a6-4f31-a26e-2b430cf93692_terseLabel_en-US" xlink:label="lab_us-gaap_ForeignCurrencyTransactionsAndTranslationsPolicyTextBlock" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Foreign Currency Translation</link:label>
    <link:label id="lab_us-gaap_ForeignCurrencyTransactionsAndTranslationsPolicyTextBlock_label_en-US" xlink:label="lab_us-gaap_ForeignCurrencyTransactionsAndTranslationsPolicyTextBlock" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Foreign Currency Transactions and Translations Policy [Policy Text Block]</link:label>
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    <link:label id="lab_us-gaap_LiabilitiesFairValueDisclosureAbstract_093ae469-579f-45ec-9699-cbdf5ea77640_terseLabel_en-US" xlink:label="lab_us-gaap_LiabilitiesFairValueDisclosureAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Liabilities</link:label>
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    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_LiabilitiesFairValueDisclosureAbstract" xlink:to="lab_us-gaap_LiabilitiesFairValueDisclosureAbstract" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_CurrentIncomeTaxExpenseBenefitContinuingOperationsAbstract_15e9afc8-0bcd-4f2f-8813-c33a21bbd8e5_terseLabel_en-US" xlink:label="lab_us-gaap_CurrentIncomeTaxExpenseBenefitContinuingOperationsAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Current provision</link:label>
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    <link:label id="lab_mrk_OtherPostretirementBenefitPlanPriorServiceCostMember_174da7d8-23e7-4bef-90cc-c2eb3f915117_terseLabel_en-US" xlink:label="lab_mrk_OtherPostretirementBenefitPlanPriorServiceCostMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Other Postretirement Benefit Plan Prior Service Credit</link:label>
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    <link:label id="lab_srt_CumulativeEffectPeriodOfAdoptionAxis_c6314eb1-9bcf-45e7-b7ef-3ce4ff2b9ac0_terseLabel_en-US" xlink:label="lab_srt_CumulativeEffectPeriodOfAdoptionAxis" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Cumulative Effect, Period of Adoption [Axis]</link:label>
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    <link:label id="lab_us-gaap_EarningsPerShareBasic_f972b90a-86da-4523-a2c4-a8b855462a89_verboseLabel_en-US" xlink:label="lab_us-gaap_EarningsPerShareBasic" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Basic Earnings per Common Share Attributable to Merck&#160;&amp; Co., Inc. Common Shareholders (in dollars per share)</link:label>
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    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_mrk_EisaiMember" xlink:to="lab_mrk_EisaiMember" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_InventoryDisclosureTextBlock_daba3bd7-e1a4-4341-9f01-d067dd4aa8bc_terseLabel_en-US" xlink:label="lab_us-gaap_InventoryDisclosureTextBlock" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Inventories</link:label>
    <link:label id="lab_us-gaap_InventoryDisclosureTextBlock_label_en-US" xlink:label="lab_us-gaap_InventoryDisclosureTextBlock" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Inventory Disclosure [Text Block]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InventoryDisclosureTextBlock" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_InventoryDisclosureTextBlock"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_InventoryDisclosureTextBlock" xlink:to="lab_us-gaap_InventoryDisclosureTextBlock" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_TradeNamesMember_5a0ea84a-2fa5-4d03-aecb-d33292d7a8bc_terseLabel_en-US" xlink:label="lab_us-gaap_TradeNamesMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Trade names</link:label>
    <link:label id="lab_us-gaap_TradeNamesMember_label_en-US" xlink:label="lab_us-gaap_TradeNamesMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Trade Names [Member]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TradeNamesMember" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_TradeNamesMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_TradeNamesMember" xlink:to="lab_us-gaap_TradeNamesMember" xlink:type="arc" order="1"/>
    <link:label id="lab_mrk_SeagenMember_1fb5a6cc-ad26-45ca-be3a-8ebff1d4f0dc_terseLabel_en-US" xlink:label="lab_mrk_SeagenMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Seagen</link:label>
    <link:label id="lab_mrk_SeagenMember_label_en-US" xlink:label="lab_mrk_SeagenMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Seagen [Member]</link:label>
    <link:label id="lab_mrk_SeagenMember_documentation_en-US" xlink:label="lab_mrk_SeagenMember" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Seagen</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_mrk_SeagenMember" xlink:href="mrk-20201231.xsd#mrk_SeagenMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_mrk_SeagenMember" xlink:to="lab_mrk_SeagenMember" xlink:type="arc" order="1"/>
    <link:label id="lab_mrk_InternationalMember_f5d397ec-c5ba-440c-b7ad-f02ef143ed9d_terseLabel_en-US" xlink:label="lab_mrk_InternationalMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Int&#8217;l</link:label>
    <link:label id="lab_mrk_InternationalMember_label_en-US" xlink:label="lab_mrk_InternationalMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">International [Member]</link:label>
    <link:label id="lab_mrk_InternationalMember_documentation_en-US" xlink:label="lab_mrk_InternationalMember" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">International [Member]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_mrk_InternationalMember" xlink:href="mrk-20201231.xsd#mrk_InternationalMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_mrk_InternationalMember" xlink:to="lab_mrk_InternationalMember" xlink:type="arc" order="1"/>
    <link:label id="lab_mrk_EffectiveIncomeTaxRateReconciliationBusinessCombinationTwo_cf6a9a5f-d805-4bef-9f93-1535ae7e2b08_terseLabel_en-US" xlink:label="lab_mrk_EffectiveIncomeTaxRateReconciliationBusinessCombinationTwo" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Acquisition of VelosBio</link:label>
    <link:label id="lab_mrk_EffectiveIncomeTaxRateReconciliationBusinessCombinationTwo_label_en-US" xlink:label="lab_mrk_EffectiveIncomeTaxRateReconciliationBusinessCombinationTwo" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Effective Income Tax Rate Reconciliation, Business Combination Two</link:label>
    <link:label id="lab_mrk_EffectiveIncomeTaxRateReconciliationBusinessCombinationTwo_documentation_en-US" xlink:label="lab_mrk_EffectiveIncomeTaxRateReconciliationBusinessCombinationTwo" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Effective Income Tax Rate Reconciliation, Business Combination Two</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_mrk_EffectiveIncomeTaxRateReconciliationBusinessCombinationTwo" xlink:href="mrk-20201231.xsd#mrk_EffectiveIncomeTaxRateReconciliationBusinessCombinationTwo"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_mrk_EffectiveIncomeTaxRateReconciliationBusinessCombinationTwo" xlink:to="lab_mrk_EffectiveIncomeTaxRateReconciliationBusinessCombinationTwo" xlink:type="arc" order="1"/>
    <link:label id="lab_dei_CurrentFiscalYearEndDate_7c0433d8-29e8-4438-a72d-e8a002913d01_terseLabel_en-US" xlink:label="lab_dei_CurrentFiscalYearEndDate" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Current Fiscal Year End Date</link:label>
    <link:label id="lab_dei_CurrentFiscalYearEndDate_label_en-US" xlink:label="lab_dei_CurrentFiscalYearEndDate" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Current Fiscal Year End Date</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CurrentFiscalYearEndDate" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_CurrentFiscalYearEndDate"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_dei_CurrentFiscalYearEndDate" xlink:to="lab_dei_CurrentFiscalYearEndDate" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_RetirementPlanSponsorLocationDomain_55087bdc-5f68-4932-9e3d-48a304393162_terseLabel_en-US" xlink:label="lab_us-gaap_RetirementPlanSponsorLocationDomain" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Retirement Plan Sponsor Location [Domain]</link:label>
    <link:label id="lab_us-gaap_RetirementPlanSponsorLocationDomain_label_en-US" xlink:label="lab_us-gaap_RetirementPlanSponsorLocationDomain" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Retirement Plan Sponsor Location [Domain]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanSponsorLocationDomain" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RetirementPlanSponsorLocationDomain"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_RetirementPlanSponsorLocationDomain" xlink:to="lab_us-gaap_RetirementPlanSponsorLocationDomain" xlink:type="arc" order="1"/>
    <link:label id="lab_mrk_FollistimAqMember_d5dfd4d3-25d3-43ae-8e22-f422d669abab_terseLabel_en-US" xlink:label="lab_mrk_FollistimAqMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Follistim AQ</link:label>
    <link:label id="lab_mrk_FollistimAqMember_label_en-US" xlink:label="lab_mrk_FollistimAqMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Follistim Aq [Member]</link:label>
    <link:label id="lab_mrk_FollistimAqMember_documentation_en-US" xlink:label="lab_mrk_FollistimAqMember" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Follistim AQ [Member].</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_mrk_FollistimAqMember" xlink:href="mrk-20201231.xsd#mrk_FollistimAqMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_mrk_FollistimAqMember" xlink:to="lab_mrk_FollistimAqMember" xlink:type="arc" order="1"/>
    <link:label id="lab_mrk_MovementinCommonStockandTreasuryStockRollForward_772cf08f-d00f-476b-a60a-252aa2969072_terseLabel_en-US" xlink:label="lab_mrk_MovementinCommonStockandTreasuryStockRollForward" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Movement in Common Stock and Treasury Stock [Roll Forward]</link:label>
    <link:label id="lab_mrk_MovementinCommonStockandTreasuryStockRollForward_label_en-US" xlink:label="lab_mrk_MovementinCommonStockandTreasuryStockRollForward" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Movement in Common Stock and Treasury Stock [Roll Forward]</link:label>
    <link:label id="lab_mrk_MovementinCommonStockandTreasuryStockRollForward_documentation_en-US" xlink:label="lab_mrk_MovementinCommonStockandTreasuryStockRollForward" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Movement in Common Stock and Treasury Stock [Roll Forward]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_mrk_MovementinCommonStockandTreasuryStockRollForward" xlink:href="mrk-20201231.xsd#mrk_MovementinCommonStockandTreasuryStockRollForward"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_mrk_MovementinCommonStockandTreasuryStockRollForward" xlink:to="lab_mrk_MovementinCommonStockandTreasuryStockRollForward" xlink:type="arc" order="1"/>
    <link:label id="lab_mrk_PharmaceuticalsegmentMember_2b088d52-d938-46e6-bee8-010f6b4cd288_terseLabel_en-US" xlink:label="lab_mrk_PharmaceuticalsegmentMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Pharmaceutical segment</link:label>
    <link:label id="lab_mrk_PharmaceuticalsegmentMember_28686503-419b-4ed9-827a-66b11b91c753_verboseLabel_en-US" xlink:label="lab_mrk_PharmaceuticalsegmentMember" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Pharmaceutical</link:label>
    <link:label id="lab_mrk_PharmaceuticalsegmentMember_label_en-US" xlink:label="lab_mrk_PharmaceuticalsegmentMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Pharmaceutical segment [Member]</link:label>
    <link:label id="lab_mrk_PharmaceuticalsegmentMember_documentation_en-US" xlink:label="lab_mrk_PharmaceuticalsegmentMember" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Pharmaceutical segment.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_mrk_PharmaceuticalsegmentMember" xlink:href="mrk-20201231.xsd#mrk_PharmaceuticalsegmentMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_mrk_PharmaceuticalsegmentMember" xlink:to="lab_mrk_PharmaceuticalsegmentMember" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill_e3074d62-eb77-46d7-a790-e4ce51d20886_terseLabel_en-US" xlink:label="lab_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Identifiable intangible assets (useful lives ranging from 18-24 years)</link:label>
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    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill" xlink:to="lab_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_d70b6410-d86b-48f0-b5bb-7e18b0cf9a16_terseLabel_en-US" xlink:label="lab_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Accumulated Other Comprehensive Income (Loss) [Line Items]</link:label>
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    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems" xlink:to="lab_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_DevelopedTechnologyRightsMember_0e2b7e08-0b34-4185-95bc-29706ba9012a_terseLabel_en-US" xlink:label="lab_us-gaap_DevelopedTechnologyRightsMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Products and product rights</link:label>
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    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_DevelopedTechnologyRightsMember" xlink:to="lab_us-gaap_DevelopedTechnologyRightsMember" xlink:type="arc" order="1"/>
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    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward" xlink:to="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_GoodwillAndIntangibleAssetImpairment_7bc57463-e6fd-4056-b0e5-3c507395e73e_terseLabel_en-US" xlink:label="lab_us-gaap_GoodwillAndIntangibleAssetImpairment" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Intangible asset impairment charges</link:label>
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    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_GoodwillAndIntangibleAssetImpairment" xlink:to="lab_us-gaap_GoodwillAndIntangibleAssetImpairment" xlink:type="arc" order="1"/>
    <link:label id="lab_mrk_AccrualForRebates_33ab93f0-fa72-4bd6-8b18-268c725860bf_terseLabel_en-US" xlink:label="lab_mrk_AccrualForRebates" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Accrual for rebates included in accrued and other current liabilities</link:label>
    <link:label id="lab_mrk_AccrualForRebates_label_en-US" xlink:label="lab_mrk_AccrualForRebates" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Accrual For Rebates</link:label>
    <link:label id="lab_mrk_AccrualForRebates_documentation_en-US" xlink:label="lab_mrk_AccrualForRebates" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Accrual for rebates recorded as current liability.</link:label>
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    <link:label id="lab_dei_LocalPhoneNumber_73f0e57b-e024-4502-8091-5c4589142bec_terseLabel_en-US" xlink:label="lab_dei_LocalPhoneNumber" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Local Phone Number</link:label>
    <link:label id="lab_dei_LocalPhoneNumber_label_en-US" xlink:label="lab_dei_LocalPhoneNumber" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Local Phone Number</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LocalPhoneNumber" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_LocalPhoneNumber"/>
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    <link:label id="lab_mrk_ViralyticsMember_label_en-US" xlink:label="lab_mrk_ViralyticsMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Viralytics [Member]</link:label>
    <link:label id="lab_mrk_ViralyticsMember_documentation_en-US" xlink:label="lab_mrk_ViralyticsMember" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Viralytics [Member]</link:label>
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    <link:label id="lab_mrk_LivestockMember_29855799-bc65-4def-8405-9fca55e33366_terseLabel_en-US" xlink:label="lab_mrk_LivestockMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Livestock</link:label>
    <link:label id="lab_mrk_LivestockMember_label_en-US" xlink:label="lab_mrk_LivestockMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Livestock [Member]</link:label>
    <link:label id="lab_mrk_LivestockMember_documentation_en-US" xlink:label="lab_mrk_LivestockMember" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Livestock [Member]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_mrk_LivestockMember" xlink:href="mrk-20201231.xsd#mrk_LivestockMember"/>
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    <link:label id="lab_mrk_ConsumercarebusinessMember_bc18a68c-31e7-46c5-96fc-2a90355cf1dd_terseLabel_en-US" xlink:label="lab_mrk_ConsumercarebusinessMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">consumer care business</link:label>
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    <link:label id="lab_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_label_en-US" xlink:label="lab_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Award Type [Domain]</link:label>
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    <link:label id="lab_mrk_CompanionAnimalsMember_5b1b66ef-ad0e-4514-8024-ca7e17987a57_terseLabel_en-US" xlink:label="lab_mrk_CompanionAnimalsMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Companion Animals</link:label>
    <link:label id="lab_mrk_CompanionAnimalsMember_label_en-US" xlink:label="lab_mrk_CompanionAnimalsMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Companion Animals [Member]</link:label>
    <link:label id="lab_mrk_CompanionAnimalsMember_documentation_en-US" xlink:label="lab_mrk_CompanionAnimalsMember" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Companion Animals [Member]</link:label>
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    <link:label id="lab_mrk_CorporateObligationsInvestmentFundsMember_5836f1d0-6713-4585-85c6-6368c83ff533_terseLabel_en-US" xlink:label="lab_mrk_CorporateObligationsInvestmentFundsMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Corporate obligations, Investment funds</link:label>
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    <link:label id="lab_mrk_CorporateObligationsInvestmentFundsMember_documentation_en-US" xlink:label="lab_mrk_CorporateObligationsInvestmentFundsMember" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Corporate obligations investment funds.</link:label>
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    <link:label id="lab_us-gaap_CorporateDebtSecuritiesMember_2204c4da-ea54-4677-84f5-0197ab78487f_terseLabel_en-US" xlink:label="lab_us-gaap_CorporateDebtSecuritiesMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Corporate notes and bonds</link:label>
    <link:label id="lab_us-gaap_CorporateDebtSecuritiesMember_label_en-US" xlink:label="lab_us-gaap_CorporateDebtSecuritiesMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Corporate Debt Securities [Member]</link:label>
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    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_CorporateDebtSecuritiesMember" xlink:to="lab_us-gaap_CorporateDebtSecuritiesMember" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_ScheduleOfRestructuringReserveByTypeOfCostTextBlock_28964b62-fba0-4943-917b-93bd42f3a5e7_terseLabel_en-US" xlink:label="lab_us-gaap_ScheduleOfRestructuringReserveByTypeOfCostTextBlock" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Charges and Spending Relating to Restructuring Activities by Program</link:label>
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    <link:label id="lab_mrk_A1.45notesdue2030Member_573d1c56-3e09-4086-9a8f-f24f297dbeb9_terseLabel_en-US" xlink:label="lab_mrk_A1.45notesdue2030Member" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">1.45% notes due 2030</link:label>
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    <link:label id="lab_mrk_A0.50eurodenominatednotesdue2024Member_18638666-810b-4861-a2b6-40fbb1621382_terseLabel_en-US" xlink:label="lab_mrk_A0.50eurodenominatednotesdue2024Member" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">0.50% euro-denominated notes due 2024</link:label>
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    <link:label id="lab_mrk_ContingentPaymentsCollaborativeArrangement_834d9b13-65fc-4932-a89a-d7912d9e4b8c_terseLabel_en-US" xlink:label="lab_mrk_ContingentPaymentsCollaborativeArrangement" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Contingent payments collaborative arrangement</link:label>
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    <link:label id="lab_mrk_ContingentPaymentsCollaborativeArrangement_documentation_en-US" xlink:label="lab_mrk_ContingentPaymentsCollaborativeArrangement" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Represents payments that may be made in the future contingent upon the achievement of regulatory and/or sales milestones as part of a collaborative arrangement.</link:label>
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    <link:label id="lab_us-gaap_TreasuryStockValue_3ad7bf0c-e170-4e6a-8fae-ec66b7556e96_terseLabel_en-US" xlink:label="lab_us-gaap_TreasuryStockValue" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Less treasury stock, at cost: 1,046,877,695 shares in 2020 and 1,038,087,496 shares in 2019</link:label>
    <link:label id="lab_us-gaap_TreasuryStockValue_label_en-US" xlink:label="lab_us-gaap_TreasuryStockValue" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Treasury Stock, Value</link:label>
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    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_TreasuryStockValue" xlink:to="lab_us-gaap_TreasuryStockValue" xlink:type="arc" order="1"/>
    <link:label id="lab_mrk_A3.875NotesDue2021Member_98a52cc8-7b31-425b-8f4c-daafb5d8cb8a_verboseLabel_en-US" xlink:label="lab_mrk_A3.875NotesDue2021Member" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">3.875% notes due 2021</link:label>
    <link:label id="lab_mrk_A3.875NotesDue2021Member_label_en-US" xlink:label="lab_mrk_A3.875NotesDue2021Member" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">3.875% Notes Due 2021 [Member]</link:label>
    <link:label id="lab_mrk_A3.875NotesDue2021Member_documentation_en-US" xlink:label="lab_mrk_A3.875NotesDue2021Member" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">3.875% Notes Due 2021</link:label>
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