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<!-- DFIN ActiveDisclosure(SM) XBRL Schema Document - http://www.dfinsolutions.com/ -->
<!-- Creation Date      : 2021-11-03T07:58:57.1141791+00:00 -->
<!-- Version            : 5.0.1.702 -->
<!-- Package ID         : f4a646f64f79433f8433d188b651af0f -->
<!-- Copyright (c) 2021 Donnelley Financial Solutions, Inc. All Rights Reserved. -->
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  <xsd:element id="hrtx_StockIssuedDuringPeriodSharesWarrantsExercised" name="StockIssuedDuringPeriodSharesWarrantsExercised" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="hrtx_StockIssuedDuringPeriodValueWarrantsExercised" name="StockIssuedDuringPeriodValueWarrantsExercised" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="hrtx_IncreaseDecreaseInClinicalLiabilities" name="IncreaseDecreaseInClinicalLiabilities" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
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  <xsd:element id="hrtx_CashCashEquivalentsAndShorttermInvestmentsPolicyTextBlock" name="CashCashEquivalentsAndShorttermInvestmentsPolicyTextBlock" type="dtr-types:textBlockItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="hrtx_ValuationAllowancesAndReservesTableTextBlock" name="ValuationAllowancesAndReservesTableTextBlock" type="dtr-types:textBlockItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="hrtx_NumberOfCountriesApprovedDrug" name="NumberOfCountriesApprovedDrug" type="xbrli:integerItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" />
  <xsd:element id="hrtx_BusinessLineItems" name="BusinessLineItems" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
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  <xsd:element id="hrtx_PercentageOfReductionInPainIntensity" name="PercentageOfReductionInPainIntensity" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="hrtx_LargestCustomerMember" name="LargestCustomerMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="hrtx_SecondLargestCustomerMember" name="SecondLargestCustomerMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
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  <xsd:element id="hrtx_TopThreeCustomersMember" name="TopThreeCustomersMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="hrtx_CINVANTIMember" name="CINVANTIMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="hrtx_SUSTOLMember" name="SUSTOLMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="hrtx_ZYNRELEFMember" name="ZYNRELEFMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="hrtx_ValuationAllowancesAndReservesProvisions" name="ValuationAllowancesAndReservesProvisions" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="hrtx_AllowanceForSalesReturns1Member" name="AllowanceForSalesReturns1Member" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="hrtx_AllowanceForDistributorFeesMember" name="AllowanceForDistributorFeesMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="hrtx_AllowanceForRebatesAndChargebacksMember" name="AllowanceForRebatesAndChargebacksMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="hrtx_UnitedStatesCommercialPaperMember" name="UnitedStatesCommercialPaperMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="hrtx_ForeignCommercialPaperMember" name="ForeignCommercialPaperMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="hrtx_TransfersAmongFairValueHierarchyLevelsAmount" name="TransfersAmongFairValueHierarchyLevelsAmount" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="hrtx_AvailableForSaleSecuritiesDebtSecuritiesCurrentContractualMaturitiesOfThreeMonthsToOneYear" name="AvailableForSaleSecuritiesDebtSecuritiesCurrentContractualMaturitiesOfThreeMonthsToOneYear" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
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  <xsd:element id="hrtx_LeasedSpaceEffectiveDate" name="LeasedSpaceEffectiveDate" type="xbrli:dateItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="hrtx_RemainingAreaOfRealEstateProperty" name="RemainingAreaOfRealEstateProperty" type="dtr-types:areaItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" />
  <xsd:element id="hrtx_AcceleratedNoncashStockOptionExpenseMember" name="AcceleratedNoncashStockOptionExpenseMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="hrtx_SeniorUnsecuredConvertibleNotesMember" name="SeniorUnsecuredConvertibleNotesMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="hrtx_SeniorSecuredConvertibleNotesMember" name="SeniorSecuredConvertibleNotesMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="hrtx_DebtInstrumentRedemptionPeriodStockPriceExceedsInPercentageOfConversionPrice" name="DebtInstrumentRedemptionPeriodStockPriceExceedsInPercentageOfConversionPrice" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="hrtx_DebtInstrumentConversionRatioMultipleOfPrincipal" name="DebtInstrumentConversionRatioMultipleOfPrincipal" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="hrtx_CommonSharesRegisteredForResaleInConnectionWithConvertibleNotes" name="CommonSharesRegisteredForResaleInConnectionWithConvertibleNotes" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="hrtx_DebtInstrumentMaturityMonthAndYear" name="DebtInstrumentMaturityMonthAndYear" type="xbrli:gYearMonthItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="hrtx_ClassOfWarrantOrRightExpirationDate" name="ClassOfWarrantOrRightExpirationDate" type="xbrli:dateItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="hrtx_ClassOfWarrantOrRightExercisedDuringPeriod" name="ClassOfWarrantOrRightExercisedDuringPeriod" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="hrtx_PreFundedWarrantsMember" name="PreFundedWarrantsMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="hrtx_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsReleasedInPeriod" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsReleasedInPeriod" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="hrtx_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsReleasedInPeriodWeightedAverageGrantDateFairValue" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsReleasedInPeriodWeightedAverageGrantDateFairValue" type="dtr-types:perShareItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
</xsd:schema>
