<SEC-DOCUMENT>0001127602-25-003685.txt : 20250207
<SEC-HEADER>0001127602-25-003685.hdr.sgml : 20250207
<ACCEPTANCE-DATETIME>20250207203649
ACCESSION NUMBER:		0001127602-25-003685
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20250206
FILED AS OF DATE:		20250207
DATE AS OF CHANGE:		20250207

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			POPS RICHARD F
		CENTRAL INDEX KEY:			0001126490
		ORGANIZATION NAME:           	
		STATE OF INCORPORATION:			DE

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-35299
		FILM NUMBER:		25603401

	MAIL ADDRESS:	
		STREET 1:		10555 SCIENCE CENTER DR
		CITY:			SAN DIEGO
		STATE:			CA
		ZIP:			92121

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			Alkermes plc.
		CENTRAL INDEX KEY:			0001520262
		STANDARD INDUSTRIAL CLASSIFICATION:	PHARMACEUTICAL PREPARATIONS [2834]
		ORGANIZATION NAME:           	03 Life Sciences
		IRS NUMBER:				981007018
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		CONNAUGHT HOUSE
		STREET 2:		1 BURLINGTON ROAD
		CITY:			DUBLIN 4
		STATE:			L2
		ZIP:			00000
		BUSINESS PHONE:		00-353-1-772-8000

	MAIL ADDRESS:	
		STREET 1:		CONNAUGHT HOUSE
		STREET 2:		1 BURLINGTON ROAD
		CITY:			DUBLIN 4
		STATE:			L2
		ZIP:			00000

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	ANTLER SCIENCE TWO PLC
		DATE OF NAME CHANGE:	20110804

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	Antler Science Two Ltd
		DATE OF NAME CHANGE:	20110509
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>form4.xml
<DESCRIPTION>PRIMARY DOCUMENT
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0508</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2025-02-06</periodOfReport>

    <issuer>
        <issuerCik>0001520262</issuerCik>
        <issuerName>Alkermes plc.</issuerName>
        <issuerTradingSymbol>ALKS</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001126490</rptOwnerCik>
            <rptOwnerName>POPS RICHARD F</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>CONNAUGHT HOUSE</rptOwnerStreet1>
            <rptOwnerStreet2>1 BURLINGTON ROAD</rptOwnerStreet2>
            <rptOwnerCity>DUBLIN 4 IRELAND</rptOwnerCity>
            <rptOwnerState></rptOwnerState>
            <rptOwnerZipCode></rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>1</isOfficer>
            <officerTitle>Director and CEO, Alkermes plc</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <aff10b5One>0</aff10b5One>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Ordinary Shares</value>
            </securityTitle>
            <transactionDate>
                <value>2025-02-06</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>190640</value>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F1"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>1370315</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Ordinary Shares</value>
            </securityTitle>
            <transactionDate>
                <value>2025-02-06</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>F</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>79925</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>31.39</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>1290390</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">These ordinary shares were acquired by the reporting person as a result of the vesting of performance-vesting restricted stock unit awards granted to the reporting person on February 18, 2022 with a three-year performance period that ended on December 31, 2024 (the &quot;2022 PRSUs&quot;). The vesting of this portion of the 2022 PRSUs was triggered by the determination of achievement of certain pre-specified performance goals and application of a total shareholder return modifier and represents the final vesting event under the 2022 PRSUs.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ Shantale Greenson, attorney-in-fact for Richard F. Pops</signatureName>
        <signatureDate>2025-02-07</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
