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    <link:label id="lab_us-gaap_ProceedsFromLicenseFeesReceived_label_en-US" xlink:label="lab_us-gaap_ProceedsFromLicenseFeesReceived" 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">Proceeds from License Fees Received</link:label>
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    <link:label id="lab_lgnd_CydexandCrystalMember_815157cb-d19f-4918-bb61-401b5481485c_terseLabel_en-US" xlink:label="lab_lgnd_CydexandCrystalMember" 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">Cydex and Crystal</link:label>
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    <link:label id="lab_us-gaap_EarningsPerShareBasicAbstract_58c720e8-26ba-49b1-87a2-86b81ff7ecf9_verboseLabel_en-US" xlink:label="lab_us-gaap_EarningsPerShareBasicAbstract" 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 per share amounts:</link:label>
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    <link:label id="lab_us-gaap_OtherSignificantNoncashTransactionValueOfConsiderationReceived1_a1829ce1-bea3-42d5-a480-b544ed2b3a65_terseLabel_en-US" xlink:label="lab_us-gaap_OtherSignificantNoncashTransactionValueOfConsiderationReceived1" 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">Value of consideration received for repayment of convertible notes</link:label>
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    <link:label id="lab_lgnd_ExercisePriceRangeFiveMember_26f20169-707e-4513-a47d-a52cf72dde11_terseLabel_en-US" xlink:label="lab_lgnd_ExercisePriceRangeFiveMember" 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">$21.92 - $21.92</link:label>
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    <link:label id="lab_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_0f79f842-3fe5-40b1-9731-8339477e588f_terseLabel_en-US" xlink:label="lab_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights" 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">Warrants issued in public offering (shares)</link:label>
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    <link:label id="lab_lgnd_PurchaseOfConvertibleBondHedge_03cb385f-018b-4773-9843-cd96a75fc8b5_negatedLabel_en-US" xlink:label="lab_lgnd_PurchaseOfConvertibleBondHedge" 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">Purchase of convertible bond hedge</link:label>
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    <link:label id="lab_lgnd_PurchaseOfConvertibleBondHedge_documentation_en-US" xlink:label="lab_lgnd_PurchaseOfConvertibleBondHedge" 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">Purchase of Convertible Bond Hedge</link:label>
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    <link:label id="lab_lgnd_VestingPeriodOneMember_3b1501e8-e2d8-4c30-bfa7-798f54f427d1_terseLabel_en-US" xlink:label="lab_lgnd_VestingPeriodOneMember" 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">Vest 1/8 on the six month anniversary of the date of grant</link:label>
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    <link:label id="lab_us-gaap_StockRepurchaseProgramAuthorizedAmount1_122646a6-4eec-45ac-839b-625fcd1bfb97_terseLabel_en-US" xlink:label="lab_us-gaap_StockRepurchaseProgramAuthorizedAmount1" 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">Stock repurchase program, authorized amount</link:label>
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    <link:label id="lab_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_636970d6-8dff-4d99-8ff6-a2a2c7cae6c9_terseLabel_en-US" xlink:label="lab_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax" 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)</link:label>
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    <link:label id="lab_us-gaap_RoyaltyMember_d985713e-e511-4a27-af2e-28f9a050b0a2_terseLabel_en-US" xlink:label="lab_us-gaap_RoyaltyMember" 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">Royalties</link:label>
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    <link:label id="lab_lgnd_OfficeEmeryvilleCAMember_documentation_en-US" xlink:label="lab_lgnd_OfficeEmeryvilleCAMember" 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">Office - Emeryville, CA [Member]</link:label>
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    <link:label id="lab_us-gaap_LiabilitiesCurrent_72ce9a40-bd3c-424c-9ece-ad9dc3f22572_totalLabel_en-US" xlink:label="lab_us-gaap_LiabilitiesCurrent" 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 current liabilities</link:label>
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    <link:label id="lab_us-gaap_ReceivablesNetCurrent_22034906-643e-4007-9dea-692b0bc6248d_verboseLabel_en-US" xlink:label="lab_us-gaap_ReceivablesNetCurrent" 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">Accounts receivable, net</link:label>
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    <link:label id="lab_us-gaap_PropertyPlantAndEquipmentTypeDomain_1a2a41ac-29d2-4ffd-b65a-e01700c7badd_terseLabel_en-US" xlink:label="lab_us-gaap_PropertyPlantAndEquipmentTypeDomain" 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 [Domain]</link:label>
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    <link:label id="lab_us-gaap_DebtInstrumentFaceAmount_9064257e-e3b8-4e67-8210-b699116e9dae_terseLabel_en-US" xlink:label="lab_us-gaap_DebtInstrumentFaceAmount" 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">Principal amount outstanding</link:label>
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    <link:label id="lab_us-gaap_UnrecognizedTaxBenefitsThatWouldImpactEffectiveTaxRate_8d9308ae-0270-4eb3-8e00-a5b5da32e74f_terseLabel_en-US" xlink:label="lab_us-gaap_UnrecognizedTaxBenefitsThatWouldImpactEffectiveTaxRate" 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 that would impact effective tax rate</link:label>
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    <link:label id="lab_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_7d07aca3-6951-41f3-bb5e-e9c53ea65dad_terseLabel_en-US" xlink:label="lab_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis" 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">Related Party [Axis]</link:label>
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    <link:label id="lab_us-gaap_LicensingAgreementsMember_26ba33d1-b0f8-4322-a33a-999c24762743_terseLabel_en-US" xlink:label="lab_us-gaap_LicensingAgreementsMember" 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">Licensing Agreements</link:label>
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    <link:label id="lab_us-gaap_FairValueOptionChangesInFairValueGainLoss1_a209349c-fb9e-47a6-8bfd-b66dd822d4f0_terseLabel_en-US" xlink:label="lab_us-gaap_FairValueOptionChangesInFairValueGainLoss1" 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">Gain on changes in fair value</link:label>
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    <link:label id="lab_lgnd_RevenueRecognitionMilestoneMethodMilestonePaymentReceived_1acd33b4-04f1-4bf0-b9dd-d83c96800aa2_terseLabel_en-US" xlink:label="lab_lgnd_RevenueRecognitionMilestoneMethodMilestonePaymentReceived" 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">Milestone payment received</link:label>
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    <link:loc xlink:type="locator" xlink:label="loc_lgnd_RevenueRecognitionMilestoneMethodMilestonePaymentReceived" xlink:href="lgnd-20181231.xsd#lgnd_RevenueRecognitionMilestoneMethodMilestonePaymentReceived"/>
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    <link:label id="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_ff5fe8f6-92d5-4cb1-a40f-2915b94f9c0f_periodStartLabel_en-US" xlink:label="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice" 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">Balance at beginning of period (USD per share)</link:label>
    <link:label id="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_145cc009-76af-44f0-96c0-97ae49d9ef67_periodEndLabel_en-US" xlink:label="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice" 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">Balance at end of period (USD per share)</link:label>
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    <link:label id="lab_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3_5a78116f-e257-4e83-b86d-0ee5ea576d7e_negatedTerseLabel_en-US" xlink:label="lab_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3" 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">Cash payment received as partial repayment of note receivable</link:label>
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    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3"/>
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    <link:label id="lab_us-gaap_IncomeTaxesPaid_a71abd8a-b915-4838-a056-00d3befd7ab4_terseLabel_en-US" xlink:label="lab_us-gaap_IncomeTaxesPaid" 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">Taxes paid</link:label>
    <link:label id="lab_us-gaap_IncomeTaxesPaid_label_en-US" xlink:label="lab_us-gaap_IncomeTaxesPaid" 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">Income Taxes Paid</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxesPaid" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_IncomeTaxesPaid"/>
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    <link:label id="lab_lgnd_EmployeeStockPurchasePlanAbstract_8ef07720-d70b-4021-83d6-3366ff031841_terseLabel_en-US" xlink:label="lab_lgnd_EmployeeStockPurchasePlanAbstract" 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">Employee Stock Purchase Plan</link:label>
    <link:label id="lab_lgnd_EmployeeStockPurchasePlanAbstract_label_en-US" xlink:label="lab_lgnd_EmployeeStockPurchasePlanAbstract" 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">Employee Stock Purchase Plan [Abstract]</link:label>
    <link:label id="lab_lgnd_EmployeeStockPurchasePlanAbstract_documentation_en-US" xlink:label="lab_lgnd_EmployeeStockPurchasePlanAbstract" 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">Employee Stock Purchase Plan [Abstract]</link:label>
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    <link:label id="lab_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage_4337c12b-5daf-4c24-b48c-35ce685353ba_terseLabel_en-US" xlink:label="lab_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage" 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">Award vesting right (as a percent)</link:label>
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    <link:label id="lab_lgnd_IncreaseDecreaseInContingentLiabilities_6cbc0212-4624-467b-833a-875d01b42241_terseLabel_en-US" xlink:label="lab_lgnd_IncreaseDecreaseInContingentLiabilities" 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 liabilities</link:label>
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    <link:loc xlink:type="locator" xlink:label="loc_lgnd_IncreaseDecreaseInContingentLiabilities" xlink:href="lgnd-20181231.xsd#lgnd_IncreaseDecreaseInContingentLiabilities"/>
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    <link:label id="lab_us-gaap_CurrentIncomeTaxExpenseBenefit_c929153c-f837-4f3f-9371-a9afd11b1583_totalLabel_en-US" xlink:label="lab_us-gaap_CurrentIncomeTaxExpenseBenefit" 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 Current Income Tax Benefit</link:label>
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    <link:label id="lab_us-gaap_NetIncomeLoss_211a903c-2b48-4f7e-9e9b-1c7bbff3edc5_totalLabel_en-US" xlink:label="lab_us-gaap_NetIncomeLoss" 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">Net income (loss)</link:label>
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    <link:label id="lab_us-gaap_NetIncomeLoss_label_en-US" xlink:label="lab_us-gaap_NetIncomeLoss" 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">Net Income (Loss) Attributable to Parent</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_NetIncomeLoss"/>
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    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1"/>
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    <link:label id="lab_us-gaap_EarningsPerShareDilutedAbstract_56de716e-fa29-4b4a-98dc-3fbc6d7d24f5_verboseLabel_en-US" xlink:label="lab_us-gaap_EarningsPerShareDilutedAbstract" 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">Diluted per share amounts:</link:label>
    <link:label id="lab_us-gaap_EarningsPerShareDilutedAbstract_34da257c-e9b1-4461-a0e4-d1f9b4c54747_terseLabel_en-US" xlink:label="lab_us-gaap_EarningsPerShareDilutedAbstract" 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">Diluted per share amounts:</link:label>
    <link:label id="lab_us-gaap_EarningsPerShareDilutedAbstract_label_en-US" xlink:label="lab_us-gaap_EarningsPerShareDilutedAbstract" 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">Earnings Per Share, Diluted [Abstract]</link:label>
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    <link:label id="lab_us-gaap_CurrentStateAndLocalTaxExpenseBenefit_577f16b7-a939-48b0-a681-0ac6f93a3d3e_terseLabel_en-US" xlink:label="lab_us-gaap_CurrentStateAndLocalTaxExpenseBenefit" 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">State</link:label>
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    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_CurrentStateAndLocalTaxExpenseBenefit" xlink:to="lab_us-gaap_CurrentStateAndLocalTaxExpenseBenefit" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_IncreaseDecreaseInContractWithCustomerLiability_424d0729-0a75-46e0-af22-71a990bf579c_terseLabel_en-US" xlink:label="lab_us-gaap_IncreaseDecreaseInContractWithCustomerLiability" 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 revenue</link:label>
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    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_IncreaseDecreaseInContractWithCustomerLiability" xlink:to="lab_us-gaap_IncreaseDecreaseInContractWithCustomerLiability" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_USGovernmentAgenciesDebtSecuritiesMember_671b684e-b38a-4793-ba21-0569a3747b6a_terseLabel_en-US" xlink:label="lab_us-gaap_USGovernmentAgenciesDebtSecuritiesMember" 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">Agency bonds</link:label>
    <link:label id="lab_us-gaap_USGovernmentAgenciesDebtSecuritiesMember_label_en-US" xlink:label="lab_us-gaap_USGovernmentAgenciesDebtSecuritiesMember" 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">US Government Agencies 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_USGovernmentAgenciesDebtSecuritiesMember" xlink:to="lab_us-gaap_USGovernmentAgenciesDebtSecuritiesMember" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_SharePrice_b7ad59b7-1c9e-46d3-9db9-f76de0c113aa_verboseLabel_en-US" xlink:label="lab_us-gaap_SharePrice" 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">Common stock price (USD per share)</link:label>
    <link:label id="lab_us-gaap_SharePrice_a0dad2fe-c8c6-4d25-a5ce-3135896b4b50_terseLabel_en-US" xlink:label="lab_us-gaap_SharePrice" 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 price (USD per share)</link:label>
    <link:label id="lab_us-gaap_SharePrice_label_en-US" xlink:label="lab_us-gaap_SharePrice" 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 Price</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharePrice" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_SharePrice"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_SharePrice" xlink:to="lab_us-gaap_SharePrice" xlink:type="arc" order="1"/>
    <link:label id="lab_lgnd_ExercisePriceRangeTenMember_816e20db-2369-4db1-b02d-4e77f583e89a_terseLabel_en-US" xlink:label="lab_lgnd_ExercisePriceRangeTenMember" 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">$85.79 - $100.38</link:label>
    <link:label id="lab_lgnd_ExercisePriceRangeTenMember_label_en-US" xlink:label="lab_lgnd_ExercisePriceRangeTenMember" 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">Exercise Price Range Ten [Member]</link:label>
    <link:label id="lab_lgnd_ExercisePriceRangeTenMember_documentation_en-US" xlink:label="lab_lgnd_ExercisePriceRangeTenMember" 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">Exercise Price Range Ten [Member]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_lgnd_ExercisePriceRangeTenMember" xlink:href="lgnd-20181231.xsd#lgnd_ExercisePriceRangeTenMember"/>
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    <link:label id="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_a4574d31-c6e8-4417-a6f3-a0327b4e8af5_periodStartLabel_en-US" xlink:label="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue" 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">Outstanding at beginning of period (USD per share)</link:label>
    <link:label id="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_08d1ac73-774f-4619-8975-b5a3ff349c3d_periodEndLabel_en-US" xlink:label="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue" 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">Outstanding at end of period (USD per share)</link:label>
    <link:label id="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_label_en-US" xlink:label="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue" 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, Weighted Average Grant Date Fair Value</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue" xlink:to="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_510ccb8a-69a8-4112-a2e5-261b50c77cf4_terseLabel_en-US" xlink:label="lab_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax" 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">Total revenues</link:label>
    <link:label id="lab_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_label_en-US" xlink:label="lab_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax" 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">Revenue from Contract with Customer, Excluding Assessed Tax</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax" xlink:to="lab_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_LeasesOperatingAbstract_2289d4b6-719c-4ba9-9063-455a1eaffae6_terseLabel_en-US" xlink:label="lab_us-gaap_LeasesOperatingAbstract" 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">Payments expected to received from sublease agreements</link:label>
    <link:label id="lab_us-gaap_LeasesOperatingAbstract_label_en-US" xlink:label="lab_us-gaap_LeasesOperatingAbstract" 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">Leases, Operating [Abstract]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LeasesOperatingAbstract" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_LeasesOperatingAbstract"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_LeasesOperatingAbstract" xlink:to="lab_us-gaap_LeasesOperatingAbstract" xlink:type="arc" order="1"/>
    <link:label id="lab_srt_OwnershipDomain_47ca8228-e03c-4b1d-b89f-d868715e7669_terseLabel_en-US" xlink:label="lab_srt_OwnershipDomain" 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">Ownership [Domain]</link:label>
    <link:label id="lab_srt_OwnershipDomain_label_en-US" xlink:label="lab_srt_OwnershipDomain" 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">Ownership [Domain]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipDomain" xlink:href="http://xbrl.fasb.org/srt/2018/elts/srt-2018-01-31.xsd#srt_OwnershipDomain"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_srt_OwnershipDomain" xlink:to="lab_srt_OwnershipDomain" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_DeferredTaxLiabilitiesInvestments_727ea2ac-897f-4bdc-af5a-32d569a00deb_negatedLabel_en-US" xlink:label="lab_us-gaap_DeferredTaxLiabilitiesInvestments" 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">Investment in Viking</link:label>
    <link:label id="lab_us-gaap_DeferredTaxLiabilitiesInvestments_label_en-US" xlink:label="lab_us-gaap_DeferredTaxLiabilitiesInvestments" 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, Investments</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredTaxLiabilitiesInvestments" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DeferredTaxLiabilitiesInvestments"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_DeferredTaxLiabilitiesInvestments" xlink:to="lab_us-gaap_DeferredTaxLiabilitiesInvestments" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalStatutoryIncomeTaxRate_e55cd388-98d6-4b4c-b564-f89b877870a5_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">Tax at federal statutory rate</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>
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    <link:label id="lab_lgnd_AdditionalRevenueRoyaltytoAcquireeShareholdersPercent_8ad2477d-efd9-49b0-818f-ff2fbfa6706f_terseLabel_en-US" xlink:label="lab_lgnd_AdditionalRevenueRoyaltytoAcquireeShareholdersPercent" 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 revenue royalty payable when higher threshold of Cydex-related revenue met (percent)</link:label>
    <link:label id="lab_lgnd_AdditionalRevenueRoyaltytoAcquireeShareholdersPercent_label_en-US" xlink:label="lab_lgnd_AdditionalRevenueRoyaltytoAcquireeShareholdersPercent" 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">Additional Revenue Royalty to Acquiree Shareholders, Percent</link:label>
    <link:label id="lab_lgnd_AdditionalRevenueRoyaltytoAcquireeShareholdersPercent_documentation_en-US" xlink:label="lab_lgnd_AdditionalRevenueRoyaltytoAcquireeShareholdersPercent" 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">Additional Revenue Royalty to Acquiree Shareholders, Percent</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_lgnd_AdditionalRevenueRoyaltytoAcquireeShareholdersPercent" xlink:href="lgnd-20181231.xsd#lgnd_AdditionalRevenueRoyaltytoAcquireeShareholdersPercent"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_lgnd_AdditionalRevenueRoyaltytoAcquireeShareholdersPercent" xlink:to="lab_lgnd_AdditionalRevenueRoyaltytoAcquireeShareholdersPercent" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_DeferredFederalIncomeTaxExpenseBenefit_c802af8b-5afe-4c22-bf7e-1f13b85d5889_terseLabel_en-US" xlink:label="lab_us-gaap_DeferredFederalIncomeTaxExpenseBenefit" 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>
    <link:label id="lab_us-gaap_DeferredFederalIncomeTaxExpenseBenefit_label_en-US" xlink:label="lab_us-gaap_DeferredFederalIncomeTaxExpenseBenefit" 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 Federal Income Tax Expense (Benefit)</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredFederalIncomeTaxExpenseBenefit" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DeferredFederalIncomeTaxExpenseBenefit"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_DeferredFederalIncomeTaxExpenseBenefit" xlink:to="lab_us-gaap_DeferredFederalIncomeTaxExpenseBenefit" 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_BusinessCombinationsPolicy" xlink:to="lab_us-gaap_BusinessCombinationsPolicy" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_ClassOfWarrantOrRightOutstanding_3c61265a-23c4-416a-8312-7b71a471e430_terseLabel_en-US" xlink:label="lab_us-gaap_ClassOfWarrantOrRightOutstanding" 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">Warrants outstanding (in shares)</link:label>
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    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightOutstanding" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ClassOfWarrantOrRightOutstanding"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ClassOfWarrantOrRightOutstanding" xlink:to="lab_us-gaap_ClassOfWarrantOrRightOutstanding" xlink:type="arc" order="1"/>
    <link:label id="lab_lgnd_OperatingLeasesFutureMinimumPaymentsDueFutureMinimumSubleaseRentalsDueinOneandTwoYears_fb6c8f4d-c5de-4cb7-a9ce-52f8087ddd4e_terseLabel_en-US" xlink:label="lab_lgnd_OperatingLeasesFutureMinimumPaymentsDueFutureMinimumSubleaseRentalsDueinOneandTwoYears" 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">Sublease payments expected to be received, 1-2 years</link:label>
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    <link:label id="lab_lgnd_DocumentAndEntityInformationAbstract_documentation_en-US" xlink:label="lab_lgnd_DocumentAndEntityInformationAbstract" 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">Document and entity information.</link:label>
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    <link:label id="lab_srt_MaximumMember_fae580c3-6e69-440c-b00c-fe81b103eee9_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>
    <link:label id="lab_srt_MaximumMember_label_en-US" xlink:label="lab_srt_MaximumMember" 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">Maximum [Member]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember" xlink:href="http://xbrl.fasb.org/srt/2018/elts/srt-2018-01-31.xsd#srt_MaximumMember"/>
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    <link:label id="lab_lgnd_ExercisePriceRangeElevenMember_cf8d788e-a726-4fe7-955b-f4fb02e46de8_terseLabel_en-US" xlink:label="lab_lgnd_ExercisePriceRangeElevenMember" 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">$8.58 &#8211; $195.91</link:label>
    <link:label id="lab_lgnd_ExercisePriceRangeElevenMember_label_en-US" xlink:label="lab_lgnd_ExercisePriceRangeElevenMember" 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">Exercise Price Range Eleven [Member]</link:label>
    <link:label id="lab_lgnd_ExercisePriceRangeElevenMember_documentation_en-US" xlink:label="lab_lgnd_ExercisePriceRangeElevenMember" 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">Exercise Price Range Eleven [Member]</link:label>
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    <link:label id="lab_us-gaap_ScheduleOfComponentsOfIncomeTaxExpenseBenefitTableTextBlock_6eaab9e6-e185-4b88-8245-78c90eaf8028_terseLabel_en-US" xlink:label="lab_us-gaap_ScheduleOfComponentsOfIncomeTaxExpenseBenefitTableTextBlock" 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 Components of Income Tax Benefit</link:label>
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    <link:label id="lab_us-gaap_DebtInstrumentConvertibleBeneficialConversionFeature_c09f6191-b758-442c-911f-2bfcd6bcd8bc_terseLabel_en-US" xlink:label="lab_us-gaap_DebtInstrumentConvertibleBeneficialConversionFeature" 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">Conversion value over the principal amount</link:label>
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    <link:label id="lab_srt_RangeMember_d50704d0-7422-43f1-b7da-5a4603d4aa21_terseLabel_en-US" xlink:label="lab_srt_RangeMember" 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">Range [Domain]</link:label>
    <link:label id="lab_srt_RangeMember_label_en-US" xlink:label="lab_srt_RangeMember" 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">Range [Domain]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember" xlink:href="http://xbrl.fasb.org/srt/2018/elts/srt-2018-01-31.xsd#srt_RangeMember"/>
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    <link:label id="lab_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseExcludingExchangeRateEffect_133ff05d-e5a3-455c-9a4b-54feca4a632a_totalLabel_en-US" xlink:label="lab_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseExcludingExchangeRateEffect" 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">Net increase (decrease) in cash and cash equivalents</link:label>
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    <link:label id="lab_us-gaap_DerivativeAssetsCurrent_9b5b9fa3-bd1e-479b-8b99-6f131a909621_terseLabel_en-US" xlink:label="lab_us-gaap_DerivativeAssetsCurrent" 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">Derivative asset</link:label>
    <link:label id="lab_us-gaap_DerivativeAssetsCurrent_label_en-US" xlink:label="lab_us-gaap_DerivativeAssetsCurrent" 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 Asset, Current</link:label>
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    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_DerivativeAssetsCurrent" xlink:to="lab_us-gaap_DerivativeAssetsCurrent" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_IncomeStatementLocationDomain_3f926f18-7b78-4b71-87fb-8185bc64340d_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>
    <link:label id="lab_us-gaap_IncomeStatementLocationDomain_label_en-US" xlink:label="lab_us-gaap_IncomeStatementLocationDomain" 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">Income Statement Location [Domain]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <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"/>
    <link:label id="lab_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_f08d2027-d36a-4a2b-a31e-f359b94e3c96_verboseLabel_en-US" xlink:label="lab_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" 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">Investing activities</link:label>
    <link:label id="lab_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_label_en-US" xlink:label="lab_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" 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">Net Cash Provided by (Used in) Investing Activities [Abstract]</link:label>
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    <link:label id="lab_us-gaap_DebtInstrumentUnamortizedPremium_884bb8cb-4969-48f3-a025-5b4116627a1c_terseLabel_en-US" xlink:label="lab_us-gaap_DebtInstrumentUnamortizedPremium" 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 issuance costs related to the liability component of convertible debt</link:label>
    <link:label id="lab_us-gaap_DebtInstrumentUnamortizedPremium_label_en-US" xlink:label="lab_us-gaap_DebtInstrumentUnamortizedPremium" 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, Unamortized Premium</link:label>
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    <link:label id="lab_us-gaap_IncomeLossFromContinuingOperationsPerBasicShare_7e6bb661-bdc9-477e-a165-cca0295e9d32_verboseLabel_en-US" xlink:label="lab_us-gaap_IncomeLossFromContinuingOperationsPerBasicShare" 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">Income (loss) from continuing operations (USD per share)</link:label>
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    <link:label id="lab_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_label_en-US" xlink:label="lab_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment" 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">Payments to Acquire Property, Plant, and Equipment</link:label>
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    <link:label id="lab_us-gaap_ConcentrationRiskCreditRisk_1f22e043-808e-44b8-b4a2-913f21c5414f_verboseLabel_en-US" xlink:label="lab_us-gaap_ConcentrationRiskCreditRisk" 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">Concentrations of Business Risk</link:label>
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    <link:label id="lab_us-gaap_RealizedInvestmentGainsLosses_b1fba51f-cbdd-42c7-8a0f-117f05c8d992_negatedTerseLabel_en-US" xlink:label="lab_us-gaap_RealizedInvestmentGainsLosses" 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">Realized gain on sale of short-term investment</link:label>
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    <link:label id="lab_us-gaap_LiabilitiesFairValueDisclosure_3265d34c-2cdf-4fcf-9a53-ea1eaedc633f_verboseLabel_en-US" xlink:label="lab_us-gaap_LiabilitiesFairValueDisclosure" 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">Liabilities, fair value</link:label>
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    <link:label id="lab_us-gaap_PaymentsForRepurchaseOfCommonStock_c5bd8a0f-f3fb-4f28-9534-0af44a8a1953_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">Share repurchases</link:label>
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    <link:label id="lab_lgnd_PaymentsToContingentValueRightHolders_9fe6f9fb-4675-47ba-9f9c-ed8bfba14761_negatedLabel_en-US" xlink:label="lab_lgnd_PaymentsToContingentValueRightHolders" 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">Payments to CVR holders and other contingency payments</link:label>
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    <link:label id="lab_us-gaap_Goodwill_d278a7ca-59b6-412e-8d37-f3912efb5811_verboseLabel_en-US" xlink:label="lab_us-gaap_Goodwill" 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">Goodwill</link:label>
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    <link:label id="lab_lgnd_LicenseFeesMilestonesAndOtherProductOtherMember_7d695cf8-1c38-4878-980b-552ae0a4ab1d_terseLabel_en-US" xlink:label="lab_lgnd_LicenseFeesMilestonesAndOtherProductOtherMember" 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_lgnd_PurchaseforCommercialLicenseRights_eeff786e-1aa2-495a-a073-a6cdc952578b_negatedLabel_en-US" xlink:label="lab_lgnd_PurchaseforCommercialLicenseRights" 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">Purchase of commercial license rights</link:label>
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    <link:label id="lab_us-gaap_BusinessAcquisitionAxis_376a859c-1737-4894-8d43-460945e095ea_terseLabel_en-US" xlink:label="lab_us-gaap_BusinessAcquisitionAxis" 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 Acquisition [Axis]</link:label>
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    <link:label id="lab_lgnd_PartnerBMember_documentation_en-US" xlink:label="lab_lgnd_PartnerBMember" 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">Partner B [Member]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_lgnd_PartnerBMember" xlink:href="lgnd-20181231.xsd#lgnd_PartnerBMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_lgnd_PartnerBMember" xlink:to="lab_lgnd_PartnerBMember" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_LongtermDebtTypeAxis_ace41091-458f-45bc-aebf-24be45840b02_terseLabel_en-US" xlink:label="lab_us-gaap_LongtermDebtTypeAxis" 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, Type [Axis]</link:label>
    <link:label id="lab_us-gaap_LongtermDebtTypeAxis_label_en-US" xlink:label="lab_us-gaap_LongtermDebtTypeAxis" 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, Type [Axis]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_LongtermDebtTypeAxis" xlink:to="lab_us-gaap_LongtermDebtTypeAxis" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_MeasurementInputTypeAxis_464ed9e0-be79-4169-9eb3-609aef83811a_terseLabel_en-US" xlink:label="lab_us-gaap_MeasurementInputTypeAxis" 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">Measurement Input Type [Axis]</link:label>
    <link:label id="lab_us-gaap_MeasurementInputTypeAxis_label_en-US" xlink:label="lab_us-gaap_MeasurementInputTypeAxis" 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">Measurement Input Type [Axis]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeAxis" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_MeasurementInputTypeAxis"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_MeasurementInputTypeAxis" xlink:to="lab_us-gaap_MeasurementInputTypeAxis" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_CurrentForeignTaxExpenseBenefit_0ee7d104-3b91-400f-a7e6-487789c29b14_terseLabel_en-US" xlink:label="lab_us-gaap_CurrentForeignTaxExpenseBenefit" 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</link:label>
    <link:label id="lab_us-gaap_CurrentForeignTaxExpenseBenefit_label_en-US" xlink:label="lab_us-gaap_CurrentForeignTaxExpenseBenefit" 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 Foreign Tax Expense (Benefit)</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CurrentForeignTaxExpenseBenefit" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_CurrentForeignTaxExpenseBenefit"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_CurrentForeignTaxExpenseBenefit" xlink:to="lab_us-gaap_CurrentForeignTaxExpenseBenefit" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis_b490a3df-9dd2-4810-84f2-76e1b3f42f2b_terseLabel_en-US" xlink:label="lab_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis" 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">Exercise Price Range [Axis]</link:label>
    <link:label id="lab_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis_label_en-US" xlink:label="lab_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis" 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">Exercise Price Range [Axis]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis" xlink:to="lab_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_OtherAssetsNoncurrent_e0720803-ecd4-4122-894a-a7cf4a583ae5_verboseLabel_en-US" xlink:label="lab_us-gaap_OtherAssetsNoncurrent" 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_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/2018/elts/us-gaap-2018-01-31.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_dei_EntityCurrentReportingStatus_a6b2e6be-e53f-4c93-8f03-56339a1e74cc_terseLabel_en-US" xlink:label="lab_dei_EntityCurrentReportingStatus" 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 Current Reporting Status</link:label>
    <link:label id="lab_dei_EntityCurrentReportingStatus_label_en-US" xlink:label="lab_dei_EntityCurrentReportingStatus" 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 Current Reporting Status</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCurrentReportingStatus" xlink:href="https://xbrl.sec.gov/dei/2018/dei-2018-01-31.xsd#dei_EntityCurrentReportingStatus"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_dei_EntityCurrentReportingStatus" xlink:to="lab_dei_EntityCurrentReportingStatus" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_ConvertibleDebtFairValueDisclosures_f31a17bf-7a07-43a1-b48f-eb5fe6854969_terseLabel_en-US" xlink:label="lab_us-gaap_ConvertibleDebtFairValueDisclosures" 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 convertible debt</link:label>
    <link:label id="lab_us-gaap_ConvertibleDebtFairValueDisclosures_4baa08e4-bdc4-40a5-887a-5f3b0fe3f4f1_verboseLabel_en-US" xlink:label="lab_us-gaap_ConvertibleDebtFairValueDisclosures" 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 convertible senior notes outstanding (Level 2)</link:label>
    <link:label id="lab_us-gaap_ConvertibleDebtFairValueDisclosures_label_en-US" xlink:label="lab_us-gaap_ConvertibleDebtFairValueDisclosures" 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">Convertible Debt, Fair Value Disclosures</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebtFairValueDisclosures" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ConvertibleDebtFairValueDisclosures"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ConvertibleDebtFairValueDisclosures" xlink:to="lab_us-gaap_ConvertibleDebtFairValueDisclosures" xlink:type="arc" order="1"/>
    <link:label id="lab_lgnd_ScheduleForShareBasedCompensationExpenseForAwardsToEmployeesAndDirectorsTableTextBlock_b5849f54-02a1-4fa3-b40a-ad03c9dcbe9d_terseLabel_en-US" xlink:label="lab_lgnd_ScheduleForShareBasedCompensationExpenseForAwardsToEmployeesAndDirectorsTableTextBlock" 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 Accounting for Share-Based Compensation</link:label>
    <link:label id="lab_lgnd_ScheduleForShareBasedCompensationExpenseForAwardsToEmployeesAndDirectorsTableTextBlock_label_en-US" xlink:label="lab_lgnd_ScheduleForShareBasedCompensationExpenseForAwardsToEmployeesAndDirectorsTableTextBlock" 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 For Share Based Compensation Expense for Awards to Employees and Directors [Table Text Block]</link:label>
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    <link:loc xlink:type="locator" xlink:label="loc_lgnd_ScheduleForShareBasedCompensationExpenseForAwardsToEmployeesAndDirectorsTableTextBlock" xlink:href="lgnd-20181231.xsd#lgnd_ScheduleForShareBasedCompensationExpenseForAwardsToEmployeesAndDirectorsTableTextBlock"/>
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    <link:label id="lab_us-gaap_EarningsPerShareDiluted_83e27c16-3803-4189-8a90-e025e9f92bd1_totalLabel_en-US" xlink:label="lab_us-gaap_EarningsPerShareDiluted" 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">Net (loss) income - Diluted (USD per share)</link:label>
    <link:label id="lab_us-gaap_EarningsPerShareDiluted_9917a9cd-78ba-454d-8cd0-1bc79286df37_verboseLabel_en-US" xlink:label="lab_us-gaap_EarningsPerShareDiluted" 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">Earnings per share - diluted (USD per share)</link:label>
    <link:label id="lab_us-gaap_EarningsPerShareDiluted_1af88dd7-d1fe-49ad-b110-58310e6a6ef3_terseLabel_en-US" xlink:label="lab_us-gaap_EarningsPerShareDiluted" 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">Net income (loss) - Diluted (USD per share)</link:label>
    <link:label id="lab_us-gaap_EarningsPerShareDiluted_label_en-US" xlink:label="lab_us-gaap_EarningsPerShareDiluted" 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">Earnings Per Share, Diluted</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareDiluted" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_EarningsPerShareDiluted"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_EarningsPerShareDiluted" xlink:to="lab_us-gaap_EarningsPerShareDiluted" xlink:type="arc" order="1"/>
    <link:label id="lab_lgnd_NonCashChangeInEstimatedFairValueOfContingentValueRights_4afbc537-6204-42af-8f75-65612469060f_negatedLabel_en-US" xlink:label="lab_lgnd_NonCashChangeInEstimatedFairValueOfContingentValueRights" 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">Change in estimated fair value of contingent liabilities</link:label>
    <link:label id="lab_lgnd_NonCashChangeInEstimatedFairValueOfContingentValueRights_label_en-US" xlink:label="lab_lgnd_NonCashChangeInEstimatedFairValueOfContingentValueRights" 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">Non-cash change in estimated fair value of contingent value rights</link:label>
    <link:label id="lab_lgnd_NonCashChangeInEstimatedFairValueOfContingentValueRights_documentation_en-US" xlink:label="lab_lgnd_NonCashChangeInEstimatedFairValueOfContingentValueRights" 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">Non-cash change in estimated fair value of contingent value rights.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_lgnd_NonCashChangeInEstimatedFairValueOfContingentValueRights" xlink:href="lgnd-20181231.xsd#lgnd_NonCashChangeInEstimatedFairValueOfContingentValueRights"/>
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    <link:label id="lab_us-gaap_OperatingCostsAndExpensesAbstract_09836ee9-afc5-4bef-bea3-8eca3a79e08a_verboseLabel_en-US" xlink:label="lab_us-gaap_OperatingCostsAndExpensesAbstract" 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">Operating costs and expenses:</link:label>
    <link:label id="lab_us-gaap_OperatingCostsAndExpensesAbstract_label_en-US" xlink:label="lab_us-gaap_OperatingCostsAndExpensesAbstract" 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 Costs and Expenses [Abstract]</link:label>
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    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_OperatingCostsAndExpensesAbstract" xlink:to="lab_us-gaap_OperatingCostsAndExpensesAbstract" xlink:type="arc" order="1"/>
    <link:label id="lab_lgnd_PartnerCMember_d46e19c7-19a3-4b89-bb00-37582daf2e64_terseLabel_en-US" xlink:label="lab_lgnd_PartnerCMember" 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">Partner C</link:label>
    <link:label id="lab_lgnd_PartnerCMember_label_en-US" xlink:label="lab_lgnd_PartnerCMember" 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">Partner C [Member]</link:label>
    <link:label id="lab_lgnd_PartnerCMember_documentation_en-US" xlink:label="lab_lgnd_PartnerCMember" 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">Partner C [Member]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_lgnd_PartnerCMember" xlink:href="lgnd-20181231.xsd#lgnd_PartnerCMember"/>
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    <link:label id="lab_us-gaap_DebtMember_daf1ac35-aeae-4ba1-a9ee-7f9f84eea2e6_terseLabel_en-US" xlink:label="lab_us-gaap_DebtMember" 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</link:label>
    <link:label id="lab_us-gaap_DebtMember_label_en-US" xlink:label="lab_us-gaap_DebtMember" 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 [Member]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtMember" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DebtMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_DebtMember" xlink:to="lab_us-gaap_DebtMember" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_InventoryNet_364aa316-80ff-496b-ad34-85c43cdc1393_verboseLabel_en-US" xlink:label="lab_us-gaap_InventoryNet" 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">Inventory</link:label>
    <link:label id="lab_us-gaap_InventoryNet_label_en-US" xlink:label="lab_us-gaap_InventoryNet" 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, Net</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InventoryNet" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_InventoryNet"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_InventoryNet" xlink:to="lab_us-gaap_InventoryNet" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions_36136ed7-956f-4e0e-91b3-a507f14c49db_verboseLabel_en-US" xlink:label="lab_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions" 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">Unrecognized compensation cost</link:label>
    <link:label id="lab_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions_label_en-US" xlink:label="lab_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions" 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">Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Stock Options</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions" xlink:to="lab_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions" xlink:type="arc" order="1"/>
    <link:label id="lab_invest_InvestmentWarrantsExercisePrice_f6ab1f09-6b5d-493d-9d2d-bd4d67abdd01_terseLabel_en-US" xlink:label="lab_invest_InvestmentWarrantsExercisePrice" 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">Exercise price, warrants (USD per share)</link:label>
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    <link:label id="lab_us-gaap_OperatingLeasesFutureMinimumPaymentsDueCurrent_370358c4-d1d9-4ff8-beb3-fd758ca5ac03_terseLabel_en-US" xlink:label="lab_us-gaap_OperatingLeasesFutureMinimumPaymentsDueCurrent" 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 lease obligation, Less than 1 year</link:label>
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    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeasesFutureMinimumPaymentsDueCurrent" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_OperatingLeasesFutureMinimumPaymentsDueCurrent"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_OperatingLeasesFutureMinimumPaymentsDueCurrent" xlink:to="lab_us-gaap_OperatingLeasesFutureMinimumPaymentsDueCurrent" xlink:type="arc" order="1"/>
    <link:label id="lab_lgnd_CommercialLicenseRightsPolicyTextBlock_b607a684-23af-4c6b-a2fb-3f030eb3ae5f_terseLabel_en-US" xlink:label="lab_lgnd_CommercialLicenseRightsPolicyTextBlock" 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">Commercial license rights</link:label>
    <link:label id="lab_lgnd_CommercialLicenseRightsPolicyTextBlock_label_en-US" xlink:label="lab_lgnd_CommercialLicenseRightsPolicyTextBlock" 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">Commercial License Rights [Policy Text Block]</link:label>
    <link:label id="lab_lgnd_CommercialLicenseRightsPolicyTextBlock_documentation_en-US" xlink:label="lab_lgnd_CommercialLicenseRightsPolicyTextBlock" 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">Commercial License Rights [Policy Text Block]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_lgnd_CommercialLicenseRightsPolicyTextBlock" xlink:href="lgnd-20181231.xsd#lgnd_CommercialLicenseRightsPolicyTextBlock"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_lgnd_CommercialLicenseRightsPolicyTextBlock" xlink:to="lab_lgnd_CommercialLicenseRightsPolicyTextBlock" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_PatentedTechnologyMember_f83157c5-529d-43b8-8183-fd1aadc84899_verboseLabel_en-US" xlink:label="lab_us-gaap_PatentedTechnologyMember" 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">Complete technology</link:label>
    <link:label id="lab_us-gaap_PatentedTechnologyMember_label_en-US" xlink:label="lab_us-gaap_PatentedTechnologyMember" 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">Patented Technology [Member]</link:label>
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    <link:label id="lab_lgnd_OperatingLeasesFutureMinimumPaymentsDueFutureMinimumSubleaseRentalsDueNextTwelveMonths_dcbd83d3-f4b6-4657-a696-f9ea6c2778a1_terseLabel_en-US" xlink:label="lab_lgnd_OperatingLeasesFutureMinimumPaymentsDueFutureMinimumSubleaseRentalsDueNextTwelveMonths" 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">Sublease payments expected to be received, Less than 1 year</link:label>
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    <link:label id="lab_lgnd_OperatingLeasesFutureMinimumPaymentsDueFutureMinimumSubleaseRentalsDueNextTwelveMonths_documentation_en-US" xlink:label="lab_lgnd_OperatingLeasesFutureMinimumPaymentsDueFutureMinimumSubleaseRentalsDueNextTwelveMonths" 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">Operating Leases, Future Minimum Payments Due, Future Minimum Sublease Rentals, Due Next Twelve Months</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_lgnd_OperatingLeasesFutureMinimumPaymentsDueFutureMinimumSubleaseRentalsDueNextTwelveMonths" xlink:href="lgnd-20181231.xsd#lgnd_OperatingLeasesFutureMinimumPaymentsDueFutureMinimumSubleaseRentalsDueNextTwelveMonths"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_lgnd_OperatingLeasesFutureMinimumPaymentsDueFutureMinimumSubleaseRentalsDueNextTwelveMonths" xlink:to="lab_lgnd_OperatingLeasesFutureMinimumPaymentsDueFutureMinimumSubleaseRentalsDueNextTwelveMonths" xlink:type="arc" order="1"/>
    <link:label id="lab_lgnd_MeasurementInputRemainingTermMember_4ca928c1-4fea-470c-aa01-b10f7a453e0d_terseLabel_en-US" xlink:label="lab_lgnd_MeasurementInputRemainingTermMember" 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">Remaining contractual term (in years)</link:label>
    <link:label id="lab_lgnd_MeasurementInputRemainingTermMember_label_en-US" xlink:label="lab_lgnd_MeasurementInputRemainingTermMember" 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">Measurement Input, Remaining Term [Member]</link:label>
    <link:label id="lab_lgnd_MeasurementInputRemainingTermMember_documentation_en-US" xlink:label="lab_lgnd_MeasurementInputRemainingTermMember" 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">Measurement Input, Remaining Term</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_lgnd_MeasurementInputRemainingTermMember" xlink:href="lgnd-20181231.xsd#lgnd_MeasurementInputRemainingTermMember"/>
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    <link:label id="lab_lgnd_AllowanceForDoubtfulAccountsPolicyTextBlock_60bb4171-6373-4938-aa07-99988cc9d774_verboseLabel_en-US" xlink:label="lab_lgnd_AllowanceForDoubtfulAccountsPolicyTextBlock" 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">Accounts Receivable</link:label>
    <link:label id="lab_lgnd_AllowanceForDoubtfulAccountsPolicyTextBlock_label_en-US" xlink:label="lab_lgnd_AllowanceForDoubtfulAccountsPolicyTextBlock" 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">Allowance For Doubtful Accounts [Policy Text Block]</link:label>
    <link:label id="lab_lgnd_AllowanceForDoubtfulAccountsPolicyTextBlock_documentation_en-US" xlink:label="lab_lgnd_AllowanceForDoubtfulAccountsPolicyTextBlock" 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">Allowance for doubtful accounts.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_lgnd_AllowanceForDoubtfulAccountsPolicyTextBlock" xlink:href="lgnd-20181231.xsd#lgnd_AllowanceForDoubtfulAccountsPolicyTextBlock"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_lgnd_AllowanceForDoubtfulAccountsPolicyTextBlock" xlink:to="lab_lgnd_AllowanceForDoubtfulAccountsPolicyTextBlock" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_f285aa92-6318-428f-9246-b59884815b57_terseLabel_en-US" xlink:label="lab_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" 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 Share-based Compensation Arrangements by Share-based Payment Award [Table]</link:label>
    <link:label id="lab_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_label_en-US" xlink:label="lab_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" 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 Share-based Compensation Arrangements by Share-based Payment Award [Table]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="lab_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation_afa538ff-99b3-47b3-92ff-42a703721500_terseLabel_en-US" xlink:label="lab_us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation" 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">Issuance of common stock under employee stock compensation plans, net</link:label>
    <link:label id="lab_us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation_label_en-US" xlink:label="lab_us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation" 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">Stock Issued During Period, Value, Share-based Compensation, Net of Forfeitures</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation" xlink:to="lab_us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation" xlink:type="arc" order="1"/>
    <link:label id="lab_lgnd_CashPayable_14062ef9-e0cd-4f05-954e-ab2a8585f9db_terseLabel_en-US" xlink:label="lab_lgnd_CashPayable" 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">Cash payable to Crystal Shareholders</link:label>
    <link:label id="lab_lgnd_CashPayable_label_en-US" xlink:label="lab_lgnd_CashPayable" 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">Cash Payable</link:label>
    <link:label id="lab_lgnd_CashPayable_documentation_en-US" xlink:label="lab_lgnd_CashPayable" 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">Cash Payable</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_lgnd_CashPayable" xlink:href="lgnd-20181231.xsd#lgnd_CashPayable"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_lgnd_CashPayable" xlink:to="lab_lgnd_CashPayable" xlink:type="arc" order="1"/>
    <link:label id="lab_lgnd_ScheduleofContingentLiabilitiesTableTextBlock_ea794d82-f565-4bd1-9b94-d68714563fb5_terseLabel_en-US" xlink:label="lab_lgnd_ScheduleofContingentLiabilitiesTableTextBlock" 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 Contingent Liabilities</link:label>
    <link:label id="lab_lgnd_ScheduleofContingentLiabilitiesTableTextBlock_label_en-US" xlink:label="lab_lgnd_ScheduleofContingentLiabilitiesTableTextBlock" 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 Contingent Liabilities [Table Text Block]</link:label>
    <link:label id="lab_lgnd_ScheduleofContingentLiabilitiesTableTextBlock_documentation_en-US" xlink:label="lab_lgnd_ScheduleofContingentLiabilitiesTableTextBlock" 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 Contingent Liabilities [Table Text Block]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_lgnd_ScheduleofContingentLiabilitiesTableTextBlock" xlink:href="lgnd-20181231.xsd#lgnd_ScheduleofContingentLiabilitiesTableTextBlock"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_lgnd_ScheduleofContingentLiabilitiesTableTextBlock" xlink:to="lab_lgnd_ScheduleofContingentLiabilitiesTableTextBlock" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_DebtDisclosureAbstract_label_en-US" xlink:label="lab_us-gaap_DebtDisclosureAbstract" 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 Disclosure [Abstract]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtDisclosureAbstract" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DebtDisclosureAbstract"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_DebtDisclosureAbstract" xlink:to="lab_us-gaap_DebtDisclosureAbstract" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_d80d4124-90aa-4aec-98a0-c20210b7cc21_terseLabel_en-US" xlink:label="lab_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward" 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:label id="lab_us-gaap_ScheduleOfNonvestedRestrictedStockUnitsActivityTableTextBlock_4c5ad245-afd3-410c-bacd-a7f98f783b28_verboseLabel_en-US" xlink:label="lab_us-gaap_ScheduleOfNonvestedRestrictedStockUnitsActivityTableTextBlock" 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">Schedule of Restricted Stock Activity</link:label>
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    <link:label id="lab_lgnd_BusinessAcquisitionContingentConsiderationPotentialCashPaymentAtEndOfPeriod_0a859fd3-bf53-4a64-a128-dd3c1d9c8253_periodStartLabel_en-US" xlink:label="lab_lgnd_BusinessAcquisitionContingentConsiderationPotentialCashPaymentAtEndOfPeriod" 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">Commercial rights at beginning of period</link:label>
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    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_lgnd_BusinessAcquisitionContingentConsiderationPotentialCashPaymentAtEndOfPeriod" xlink:to="lab_lgnd_BusinessAcquisitionContingentConsiderationPotentialCashPaymentAtEndOfPeriod" xlink:type="arc" order="1"/>
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    <link:label id="lab_us-gaap_OfficeEquipmentMember_30abe888-84aa-4281-b5ab-ef66601d2c78_verboseLabel_en-US" xlink:label="lab_us-gaap_OfficeEquipmentMember" 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">Lab and office equipment</link:label>
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    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_OtherAccruedLiabilitiesCurrent" xlink:to="lab_us-gaap_OtherAccruedLiabilitiesCurrent" 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_AccumulatedOtherComprehensiveIncomeMember" xlink:to="lab_us-gaap_AccumulatedOtherComprehensiveIncomeMember" xlink:type="arc" order="1"/>
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    <link:label id="lab_lgnd_ThresholdRevenueAmounttoTriggerAdditionalRoyaltyPayments_documentation_en-US" xlink:label="lab_lgnd_ThresholdRevenueAmounttoTriggerAdditionalRoyaltyPayments" 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">Threshold Revenue Amount to Trigger Additional Royalty Payments</link:label>
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    <link:label id="lab_us-gaap_CommonStockSharesAuthorized_3f66792b-c246-419d-a6cf-00b8d3b04f3a_verboseLabel_en-US" xlink:label="lab_us-gaap_CommonStockSharesAuthorized" 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">Common stock, shares authorized (shares)</link:label>
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    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesAuthorized" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_CommonStockSharesAuthorized"/>
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    <link:label id="lab_srt_ProductsAndServicesDomain_05e3983e-a78f-4103-9815-cb5c87b0cfe6_terseLabel_en-US" xlink:label="lab_srt_ProductsAndServicesDomain" 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 and Service [Domain]</link:label>
    <link:label id="lab_srt_ProductsAndServicesDomain_label_en-US" xlink:label="lab_srt_ProductsAndServicesDomain" 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">Product and Service [Domain]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain" xlink:href="http://xbrl.fasb.org/srt/2018/elts/srt-2018-01-31.xsd#srt_ProductsAndServicesDomain"/>
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    <link:label id="lab_lgnd_OwnershipInEntityByDirectorPercentage_b0de2b3e-e2b6-4306-8cbd-e13b350d51ca_terseLabel_en-US" xlink:label="lab_lgnd_OwnershipInEntityByDirectorPercentage" 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">Ownership in entity by director (as a percent)</link:label>
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    <link:label id="lab_lgnd_OwnershipInEntityByDirectorPercentage_documentation_en-US" xlink:label="lab_lgnd_OwnershipInEntityByDirectorPercentage" 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">Ownership in Entity by Director, Percentage</link:label>
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    <link:label id="lab_us-gaap_TypeOfAdoptionMember_6b4c47bc-6a02-424e-a4bb-d941ad4a5dd2_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>
    <link:label id="lab_us-gaap_TypeOfAdoptionMember_label_en-US" xlink:label="lab_us-gaap_TypeOfAdoptionMember" 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">Type of Adoption [Domain]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfAdoptionMember" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_TypeOfAdoptionMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_TypeOfAdoptionMember" xlink:to="lab_us-gaap_TypeOfAdoptionMember" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_UnrecognizedTaxBenefitsDecreasesResultingFromPriorPeriodTaxPositions_a7f07d8c-17ef-4ef3-be09-74a5b226470d_negatedTerseLabel_en-US" xlink:label="lab_us-gaap_UnrecognizedTaxBenefitsDecreasesResultingFromPriorPeriodTaxPositions" 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">Reductions for tax positions of prior years</link:label>
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    <link:label id="lab_lgnd_ExercisePriceRangeTwoMember_4994833f-3393-4a17-b6a0-9e3d6096f889_terseLabel_en-US" xlink:label="lab_lgnd_ExercisePriceRangeTwoMember" 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">$10.12 - $12.81</link:label>
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    <link:loc xlink:type="locator" xlink:label="loc_lgnd_ExercisePriceRangeTwoMember" xlink:href="lgnd-20181231.xsd#lgnd_ExercisePriceRangeTwoMember"/>
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    <link:label id="lab_us-gaap_FairValueDisclosuresAbstract_label_en-US" xlink:label="lab_us-gaap_FairValueDisclosuresAbstract" 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 Disclosures [Abstract]</link:label>
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    <link:label id="lab_dei_EntityShellCompany_6eec8cac-7821-476c-80a5-85bfb1edc517_terseLabel_en-US" xlink:label="lab_dei_EntityShellCompany" 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 Shell Company</link:label>
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    <link:label id="lab_us-gaap_ShareBasedCompensationOptionAndIncentivePlansPolicy_43482946-76c0-4801-a6ce-c5603618bfe8_verboseLabel_en-US" xlink:label="lab_us-gaap_ShareBasedCompensationOptionAndIncentivePlansPolicy" 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">Share-Based Compensation</link:label>
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    <link:label id="lab_us-gaap_MeasurementInputExpectedDividendRateMember_0e20e46b-8614-427b-aadf-f0292c3e10eb_terseLabel_en-US" xlink:label="lab_us-gaap_MeasurementInputExpectedDividendRateMember" 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">Dividend yield</link:label>
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    <link:label id="lab_us-gaap_PaymentsToAcquireShortTermInvestments_9d023fe7-2cc9-4a8e-b398-c34b727b2050_negatedTerseLabel_en-US" xlink:label="lab_us-gaap_PaymentsToAcquireShortTermInvestments" 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">Purchases of short-term investments</link:label>
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    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireShortTermInvestments" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_PaymentsToAcquireShortTermInvestments"/>
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    <link:label id="lab_us-gaap_StockholdersEquity_bcf41725-b90c-427a-a335-a675de111bbe_totalLabel_en-US" xlink:label="lab_us-gaap_StockholdersEquity" 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 stockholders&#8217; equity</link:label>
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    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_StockholdersEquity" xlink:to="lab_us-gaap_StockholdersEquity" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_PlanNameAxis_1c47d015-4ef9-4438-8b57-e14866cb0759_terseLabel_en-US" xlink:label="lab_us-gaap_PlanNameAxis" 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">Plan Name [Axis]</link:label>
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    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_PlanNameAxis" xlink:to="lab_us-gaap_PlanNameAxis" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_VariableInterestEntityDisclosureTextBlock_3fb4544c-9908-440b-b582-d0d90f2bd061_terseLabel_en-US" xlink:label="lab_us-gaap_VariableInterestEntityDisclosureTextBlock" 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">Investment in Viking</link:label>
    <link:label id="lab_us-gaap_VariableInterestEntityDisclosureTextBlock_label_en-US" xlink:label="lab_us-gaap_VariableInterestEntityDisclosureTextBlock" 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">Variable Interest Entity Disclosure [Text Block]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableInterestEntityDisclosureTextBlock" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_VariableInterestEntityDisclosureTextBlock"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_VariableInterestEntityDisclosureTextBlock" xlink:to="lab_us-gaap_VariableInterestEntityDisclosureTextBlock" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_EquityComponentDomain_20331d7e-c2f5-4e78-9ac9-eceb7a373d45_terseLabel_en-US" xlink:label="lab_us-gaap_EquityComponentDomain" 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">Total stockholders&#8217; equity</link:label>
    <link:label id="lab_us-gaap_EquityComponentDomain_6489f36f-ea5b-4aa9-8380-d41e5557bb6a_verboseLabel_en-US" xlink:label="lab_us-gaap_EquityComponentDomain" 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">Equity Component [Domain]</link:label>
    <link:label id="lab_us-gaap_EquityComponentDomain_label_en-US" xlink:label="lab_us-gaap_EquityComponentDomain" 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">Equity Component [Domain]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_EquityComponentDomain"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_EquityComponentDomain" xlink:to="lab_us-gaap_EquityComponentDomain" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_GoodwillAndIntangibleAssetsGoodwillPolicy_42119d68-22c4-4cd6-91cf-cb101ac798e1_terseLabel_en-US" xlink:label="lab_us-gaap_GoodwillAndIntangibleAssetsGoodwillPolicy" 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, Intangible Assets and Other Long-Lived Assets</link:label>
    <link:label id="lab_us-gaap_GoodwillAndIntangibleAssetsGoodwillPolicy_label_en-US" xlink:label="lab_us-gaap_GoodwillAndIntangibleAssetsGoodwillPolicy" 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 and Intangible Assets, Goodwill, Policy [Policy Text Block]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillAndIntangibleAssetsGoodwillPolicy" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_GoodwillAndIntangibleAssetsGoodwillPolicy"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_GoodwillAndIntangibleAssetsGoodwillPolicy" xlink:to="lab_us-gaap_GoodwillAndIntangibleAssetsGoodwillPolicy" xlink:type="arc" order="1"/>
    <link:label id="lab_lgnd_AmendedESPPMember_74bdd270-4cde-45af-8ddf-e397d88c1955_terseLabel_en-US" xlink:label="lab_lgnd_AmendedESPPMember" 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">Amended ESPP</link:label>
    <link:label id="lab_lgnd_AmendedESPPMember_label_en-US" xlink:label="lab_lgnd_AmendedESPPMember" 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">Amended ESPP [Member]</link:label>
    <link:label id="lab_lgnd_AmendedESPPMember_documentation_en-US" xlink:label="lab_lgnd_AmendedESPPMember" 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">Amended ESPP [Member]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_lgnd_AmendedESPPMember" xlink:href="lgnd-20181231.xsd#lgnd_AmendedESPPMember"/>
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    <link:label id="lab_lgnd_AdjustmentsToAdditionalPaidInCapitalWarrantsSettled_fa01eda0-65a4-421c-9e0e-cb453cf299c8_terseLabel_en-US" xlink:label="lab_lgnd_AdjustmentsToAdditionalPaidInCapitalWarrantsSettled" 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">Deduction to additional paid-in-capital for warrants settled</link:label>
    <link:label id="lab_lgnd_AdjustmentsToAdditionalPaidInCapitalWarrantsSettled_label_en-US" xlink:label="lab_lgnd_AdjustmentsToAdditionalPaidInCapitalWarrantsSettled" 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">Adjustments to Additional Paid in Capital, Warrants Settled</link:label>
    <link:label id="lab_lgnd_AdjustmentsToAdditionalPaidInCapitalWarrantsSettled_documentation_en-US" xlink:label="lab_lgnd_AdjustmentsToAdditionalPaidInCapitalWarrantsSettled" 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">Adjustments to Additional Paid in Capital, Warrants Settled</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_lgnd_AdjustmentsToAdditionalPaidInCapitalWarrantsSettled" xlink:href="lgnd-20181231.xsd#lgnd_AdjustmentsToAdditionalPaidInCapitalWarrantsSettled"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_lgnd_AdjustmentsToAdditionalPaidInCapitalWarrantsSettled" xlink:to="lab_lgnd_AdjustmentsToAdditionalPaidInCapitalWarrantsSettled" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_CommonStockMember_ee378653-0924-46e4-809d-ddd016e0ab47_terseLabel_en-US" xlink:label="lab_us-gaap_CommonStockMember" 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</link:label>
    <link:label id="lab_us-gaap_CommonStockMember_label_en-US" xlink:label="lab_us-gaap_CommonStockMember" 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">Common Stock [Member]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_CommonStockMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_CommonStockMember" xlink:to="lab_us-gaap_CommonStockMember" xlink:type="arc" order="1"/>
    <link:label id="lab_lgnd_ThresholdofRevenuesabove1.5millionwithFourCollaborationAgreementsMember_ffa7bb38-ed41-42c5-ab77-27d9680ba1b8_terseLabel_en-US" xlink:label="lab_lgnd_ThresholdofRevenuesabove1.5millionwithFourCollaborationAgreementsMember" 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">Threshold of Revenues above $1.5 million with Four Collaboration Agreements</link:label>
    <link:label id="lab_lgnd_ThresholdofRevenuesabove1.5millionwithFourCollaborationAgreementsMember_label_en-US" xlink:label="lab_lgnd_ThresholdofRevenuesabove1.5millionwithFourCollaborationAgreementsMember" 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">Threshold of Revenues above $1.5 million with Four Collaboration Agreements [Member]</link:label>
    <link:label id="lab_lgnd_ThresholdofRevenuesabove1.5millionwithFourCollaborationAgreementsMember_documentation_en-US" xlink:label="lab_lgnd_ThresholdofRevenuesabove1.5millionwithFourCollaborationAgreementsMember" 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">Threshold of Revenues above $1.5 million with Four Collaboration Agreements [Member]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_lgnd_ThresholdofRevenuesabove1.5millionwithFourCollaborationAgreementsMember" xlink:href="lgnd-20181231.xsd#lgnd_ThresholdofRevenuesabove1.5millionwithFourCollaborationAgreementsMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_lgnd_ThresholdofRevenuesabove1.5millionwithFourCollaborationAgreementsMember" xlink:to="lab_lgnd_ThresholdofRevenuesabove1.5millionwithFourCollaborationAgreementsMember" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_DebtInstrumentInterestRateStatedPercentage_d8310de6-c850-4f36-b05b-ad5c0d0693ac_terseLabel_en-US" xlink:label="lab_us-gaap_DebtInstrumentInterestRateStatedPercentage" 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 on debt instrument (as a percent)</link:label>
    <link:label id="lab_us-gaap_DebtInstrumentInterestRateStatedPercentage_label_en-US" xlink:label="lab_us-gaap_DebtInstrumentInterestRateStatedPercentage" 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, Interest Rate, Stated Percentage</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage" xlink:to="lab_us-gaap_DebtInstrumentInterestRateStatedPercentage" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_IncomeTaxReconciliationNondeductibleExpenseShareBasedCompensationCost_c086f7a6-b68b-4800-b907-57e9fc98f28b_terseLabel_en-US" xlink:label="lab_us-gaap_IncomeTaxReconciliationNondeductibleExpenseShareBasedCompensationCost" 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">Stock-based compensation</link:label>
    <link:label id="lab_us-gaap_IncomeTaxReconciliationNondeductibleExpenseShareBasedCompensationCost_label_en-US" xlink:label="lab_us-gaap_IncomeTaxReconciliationNondeductibleExpenseShareBasedCompensationCost" 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, Share-based Compensation Cost, Amount</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxReconciliationNondeductibleExpenseShareBasedCompensationCost" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_IncomeTaxReconciliationNondeductibleExpenseShareBasedCompensationCost"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_IncomeTaxReconciliationNondeductibleExpenseShareBasedCompensationCost" xlink:to="lab_us-gaap_IncomeTaxReconciliationNondeductibleExpenseShareBasedCompensationCost" xlink:type="arc" order="1"/>
    <link:label id="lab_lgnd_AdjustmentsToAdditionalPaidInCapitalWarrantsRepurchased_7202eecd-6cc9-46f1-8364-6cadd565f71d_negatedLabel_en-US" xlink:label="lab_lgnd_AdjustmentsToAdditionalPaidInCapitalWarrantsRepurchased" 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">Warrant repurchase</link:label>
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    <link:label id="lab_lgnd_AdjustmentsToAdditionalPaidInCapitalWarrantsRepurchased_documentation_en-US" xlink:label="lab_lgnd_AdjustmentsToAdditionalPaidInCapitalWarrantsRepurchased" 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">Adjustments to Additional Paid in Capital, Warrants Repurchased</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_lgnd_AdjustmentsToAdditionalPaidInCapitalWarrantsRepurchased" xlink:href="lgnd-20181231.xsd#lgnd_AdjustmentsToAdditionalPaidInCapitalWarrantsRepurchased"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_lgnd_AdjustmentsToAdditionalPaidInCapitalWarrantsRepurchased" xlink:to="lab_lgnd_AdjustmentsToAdditionalPaidInCapitalWarrantsRepurchased" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber_f337e10b-6cb4-4fe4-a704-802ad1d97832_verboseLabel_en-US" xlink:label="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber" 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">Exercisable at end of period (shares)</link:label>
    <link:label id="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber_label_en-US" xlink:label="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber" 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, Options, Exercisable, Number</link:label>
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    <link:label id="lab_us-gaap_AccountsPayableCurrent_190b1ea6-c39f-4fc5-8bd8-8c04f388d102_verboseLabel_en-US" xlink:label="lab_us-gaap_AccountsPayableCurrent" 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">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/2018/elts/us-gaap-2018-01-31.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_NotesPayableCurrent_570145c0-a596-4ff1-970f-331af414fa40_terseLabel_en-US" xlink:label="lab_us-gaap_NotesPayableCurrent" 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">Total current portion of notes payable</link:label>
    <link:label id="lab_us-gaap_NotesPayableCurrent_label_en-US" xlink:label="lab_us-gaap_NotesPayableCurrent" 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">Notes Payable, Current</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NotesPayableCurrent" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_NotesPayableCurrent"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_NotesPayableCurrent" xlink:to="lab_us-gaap_NotesPayableCurrent" xlink:type="arc" order="1"/>
    <link:label id="lab_lgnd_LicenseFeesMilestonesandProductOtherMember_4152d3bd-d769-4c0f-89a4-4b9119f01d93_terseLabel_en-US" xlink:label="lab_lgnd_LicenseFeesMilestonesandProductOtherMember" 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">License fees, milestones and other revenues</link:label>
    <link:label id="lab_lgnd_LicenseFeesMilestonesandProductOtherMember_label_en-US" xlink:label="lab_lgnd_LicenseFeesMilestonesandProductOtherMember" 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">License Fees, Milestones, and Product, Other [Member]</link:label>
    <link:label id="lab_lgnd_LicenseFeesMilestonesandProductOtherMember_documentation_en-US" xlink:label="lab_lgnd_LicenseFeesMilestonesandProductOtherMember" 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">License Fees, Milestones, and Product, Other [Member]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_lgnd_LicenseFeesMilestonesandProductOtherMember" xlink:href="lgnd-20181231.xsd#lgnd_LicenseFeesMilestonesandProductOtherMember"/>
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    <link:label id="lab_us-gaap_ResearchAndDevelopmentExpense_951e3692-1736-4da7-b197-a994ec4220ec_verboseLabel_en-US" xlink:label="lab_us-gaap_ResearchAndDevelopmentExpense" 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">Research and development</link:label>
    <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:label id="lab_lgnd_Phase3ClinicalTrialMember_6ff8ba9e-d96c-482c-8e9f-c007ffd9af4d_terseLabel_en-US" xlink:label="lab_lgnd_Phase3ClinicalTrialMember" 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">Phase 3 Clinical Trial</link:label>
    <link:label id="lab_lgnd_Phase3ClinicalTrialMember_label_en-US" xlink:label="lab_lgnd_Phase3ClinicalTrialMember" 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">Phase 3 Clinical Trial [Member]</link:label>
    <link:label id="lab_lgnd_Phase3ClinicalTrialMember_documentation_en-US" xlink:label="lab_lgnd_Phase3ClinicalTrialMember" 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">Phase 3 Clinical Trial</link:label>
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    <link:label id="lab_us-gaap_USTreasurySecuritiesMember_ac177ee8-a986-4de2-ab71-2be4b705ba59_terseLabel_en-US" xlink:label="lab_us-gaap_USTreasurySecuritiesMember" 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. Government bonds</link:label>
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    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_USTreasurySecuritiesMember" xlink:to="lab_us-gaap_USTreasurySecuritiesMember" xlink:type="arc" order="1"/>
    <link:label id="lab_lgnd_VestingPeriodTwoMember_53faf313-65a0-46e3-a4e0-77abb64e2518_terseLabel_en-US" xlink:label="lab_lgnd_VestingPeriodTwoMember" 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">Vest 1/48 each month for forty-two months</link:label>
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    <link:label id="lab_us-gaap_OperatingLeasedAssetsLineItems_8c0be524-d77f-4bc2-9719-3d9202dc2738_terseLabel_en-US" xlink:label="lab_us-gaap_OperatingLeasedAssetsLineItems" 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 Leased Assets [Line Items]</link:label>
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    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeasedAssetsLineItems" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_OperatingLeasedAssetsLineItems"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_OperatingLeasedAssetsLineItems" xlink:to="lab_us-gaap_OperatingLeasedAssetsLineItems" xlink:type="arc" order="1"/>
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    <link:label id="lab_us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption_b5f881ac-f7fe-4a36-b017-6c0d5c380da7_terseLabel_en-US" xlink:label="lab_us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption" 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 adjustment from adoption of ASU</link:label>
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    <link:label id="lab_us-gaap_NotesAndLoansReceivableGrossCurrent_ed34d575-b97a-4215-bd64-c417e0fbcbd8_terseLabel_en-US" xlink:label="lab_us-gaap_NotesAndLoansReceivableGrossCurrent" 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">Note receivable from Viking</link:label>
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    <link:label id="lab_us-gaap_ProceedsFromIssuanceOfWarrants_56c8387e-f72f-46f4-b394-69babb34429e_terseLabel_en-US" xlink:label="lab_us-gaap_ProceedsFromIssuanceOfWarrants" 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">Proceeds from issuance of warrants</link:label>
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    <link:label id="lab_lgnd_SelexisMember_documentation_en-US" xlink:label="lab_lgnd_SelexisMember" 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">Selexis [Member]</link:label>
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    <link:label id="lab_us-gaap_ProfitLoss_6516e29e-472e-4fde-8e0e-01417ad1864b_totalLabel_en-US" xlink:label="lab_us-gaap_ProfitLoss" 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">Net income (loss)</link:label>
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    <link:label id="lab_us-gaap_DebtInstrumentRedemptionPeriodTwoMember_70b997d8-9b4a-43ff-8c3b-5085c8664746_terseLabel_en-US" xlink:label="lab_us-gaap_DebtInstrumentRedemptionPeriodTwoMember" 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">Redemption Period Two</link:label>
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    <link:label id="lab_lgnd_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedRestrictedCash_6bb3b97e-b7b2-4bde-9ef6-2fd42731de2f_terseLabel_en-US" xlink:label="lab_lgnd_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedRestrictedCash" 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">Restricted cash</link:label>
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    <link:label id="lab_us-gaap_NonoperatingIncomeExpense_e568aeae-e645-4ae9-80a7-2c3085e2584e_totalLabel_en-US" xlink:label="lab_us-gaap_NonoperatingIncomeExpense" 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 other income (expense), net</link:label>
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