<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0206</schemaVersion>

    <documentType>3</documentType>

    <periodOfReport>2023-10-10</periodOfReport>

    <noSecuritiesOwned>1</noSecuritiesOwned>

    <issuer>
        <issuerCik>0001444192</issuerCik>
        <issuerName>Acasti Pharma Inc.</issuerName>
        <issuerTradingSymbol>ACST</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001184432</rptOwnerCik>
            <rptOwnerName>DAVIS A BRIAN</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O ACASTI PHARMA INC.</rptOwnerStreet1>
            <rptOwnerStreet2>2572 BOUL. DANIEL-JOHNSON, 2ND FLOOR</rptOwnerStreet2>
            <rptOwnerCity>LAVAL</rptOwnerCity>
            <rptOwnerState>A8</rptOwnerState>
            <rptOwnerZipCode>H7T 2R3</rptOwnerZipCode>
            <rptOwnerStateDescription>QUEBEC, CANADA</rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <ownerSignature>
        <signatureName>/s/ A. Brian Davis</signatureName>
        <signatureDate>2023-10-20</signatureDate>
    </ownerSignature>
</ownershipDocument>
