<?xml version="1.0" encoding="us-ascii"?>
<!-- DFIN ActiveDisclosure(SM) XBRL Schema Document - http://www.dfinsolutions.com/ -->
<!-- Creation Date      : 2020-11-05T02:57:13.7459965+00:00 -->
<!-- Version            : 5.0.1.513 -->
<!-- Package ID         : 6937a5421efa4cccaa9ebd4eb187b7b4 -->
<!-- Copyright (c) 2020 Donnelley Financial Solutions, Inc. All Rights Reserved. -->
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  <xsd:element id="amrn_StockIncentivePlanTwentyElevenMember" name="StockIncentivePlanTwentyElevenMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="amrn_PerformanceBasedRestrictedStockUnitsMember" name="PerformanceBasedRestrictedStockUnitsMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="amrn_EmployeesMember" name="EmployeesMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="amrn_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalGrantsInPeriod" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalGrantsInPeriod" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="amrn_AgreementAmendedYear" name="AgreementAmendedYear" type="xbrli:gYearItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="amrn_CoPromotionAgreementLineItems" name="CoPromotionAgreementLineItems" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="amrn_CoPromotionAgreementTable" name="CoPromotionAgreementTable" type="xbrli:stringItemType" substitutionGroup="xbrldt:hypercubeItem" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="amrn_CoPromotionAgreementMember" name="CoPromotionAgreementMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="amrn_KowaPharmaceuticalsAmericaIncorporationMember" name="KowaPharmaceuticalsAmericaIncorporationMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="amrn_MaximumCoPromotionTailPaymentsReceivePeriod" name="MaximumCoPromotionTailPaymentsReceivePeriod" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="amrn_PercentageOfGrossMarginPayableForPromotionAgreement" name="PercentageOfGrossMarginPayableForPromotionAgreement" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="amrn_CoPromotionTailPaymentsReceivable" name="CoPromotionTailPaymentsReceivable" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="amrn_AccruedCoPromotionTailPayments" name="AccruedCoPromotionTailPayments" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="amrn_VASCEPAOneGramMember" name="VASCEPAOneGramMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="amrn_VASCEPAHalfGramMember" name="VASCEPAHalfGramMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="amrn_CashDiscountPercent" name="CashDiscountPercent" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" />
  <xsd:element id="amrn_ProductExpirationPeriodUponConversionIntoCapsuleForm" name="ProductExpirationPeriodUponConversionIntoCapsuleForm" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="amrn_ProvisionRelatedToPriorPeriodSales" name="ProvisionRelatedToPriorPeriodSales" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="amrn_CreditsPaymentsMadeForPriorPeriodSales" name="CreditsPaymentsMadeForPriorPeriodSales" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="amrn_ValuationAllowancesProvisionsAndReservesBalanceNet" name="ValuationAllowancesProvisionsAndReservesBalanceNet" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="amrn_RebatesChargebacksAndDiscountsMember" name="RebatesChargebacksAndDiscountsMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="amrn_ProductReturnsMember" name="ProductReturnsMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="amrn_OtherIncentiveProgramsMember" name="OtherIncentiveProgramsMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="amrn_NonRefundableAndNonCreditableUpfrontPayment" name="NonRefundableAndNonCreditableUpfrontPayment" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="amrn_PaymentOfMilestones" name="PaymentOfMilestones" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="amrn_LicenseAndCollaborationAgreementsLineItems" name="LicenseAndCollaborationAgreementsLineItems" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="amrn_LicenseAndCollaborationAgreementsTable" name="LicenseAndCollaborationAgreementsTable" type="xbrli:stringItemType" substitutionGroup="xbrldt:hypercubeItem" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="amrn_MochidaPharmaceuticalCoLtdMember" name="MochidaPharmaceuticalCoLtdMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="amrn_InLicensesAgreementMember" name="InLicensesAgreementMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="amrn_EddingpharmMember" name="EddingpharmMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="amrn_OutLicensesAgreementMember" name="OutLicensesAgreementMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="amrn_ClinicalTrialApplicationMember" name="ClinicalTrialApplicationMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="amrn_BiologixMember" name="BiologixMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="amrn_HLSTherapeuticsIncorporationMember" name="HLSTherapeuticsIncorporationMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="amrn_NonRefundableUpfrontPaymentsReceived" name="NonRefundableUpfrontPaymentsReceived" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="amrn_NonrefundableMilestonePayment" name="NonrefundableMilestonePayment" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="amrn_EligibleMilestonePayment" name="EligibleMilestonePayment" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="amrn_NumberOfRegulatoryMilestoneEventsIndications" name="NumberOfRegulatoryMilestoneEventsIndications" type="xbrli:integerItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="amrn_EligibleRegulatoryMilestoneEventPayment" name="EligibleRegulatoryMilestoneEventPayment" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="amrn_EligibleSalesBasedMilestoneEventPayment" name="EligibleSalesBasedMilestoneEventPayment" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="amrn_DeferredRevenueRecognitionPeriod" name="DeferredRevenueRecognitionPeriod" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="amrn_NonRefundableUpfrontPaymentsReceivedPeriod" name="NonRefundableUpfrontPaymentsReceivedPeriod" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="amrn_NonrefundableMilestonePaymentReceived" name="NonrefundableMilestonePaymentReceived" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="amrn_ContractWithCustomerAssetsAdditions" name="ContractWithCustomerAssetsAdditions" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="amrn_ContractWithCustomerAssetDeductions" name="ContractWithCustomerAssetDeductions" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="amrn_ContractWithCustomerLiabilityAdditions" name="ContractWithCustomerLiabilityAdditions" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="amrn_ContractWithCustomerLiabilityRevenueRecognizedExcludingPerformanceObligationSatisfiedInPreviousPeriod" name="ContractWithCustomerLiabilityRevenueRecognizedExcludingPerformanceObligationSatisfiedInPreviousPeriod" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="amrn_ShortTermLeasePeriod" name="ShortTermLeasePeriod" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="amrn_LocationAxis" name="LocationAxis" type="xbrli:stringItemType" substitutionGroup="xbrldt:dimensionItem" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="amrn_LocationsDomain" name="LocationsDomain" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="amrn_DublinMember" name="DublinMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="amrn_OfficeCentreSharingAgreementsMember" name="OfficeCentreSharingAgreementsMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="amrn_OfficeCentreSharingAgreementsEffectiveMayOneTwoThousandAndNineteenMember" name="OfficeCentreSharingAgreementsEffectiveMayOneTwoThousandAndNineteenMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="amrn_BridgewaterMember" name="BridgewaterMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="amrn_OperatingLeaseChangeInWeightedAverageDiscountRatePercent" name="OperatingLeaseChangeInWeightedAverageDiscountRatePercent" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="amrn_LesseeOperatingLeaseOptionToAdditionalExtend" name="LesseeOperatingLeaseOptionToAdditionalExtend" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="amrn_OperatingLeaseCommencementDate" name="OperatingLeaseCommencementDate" type="xbrli:dateItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="amrn_NumberOfRenewalOptions" name="NumberOfRenewalOptions" type="xbrli:integerItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" />
</xsd:schema>
