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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2018-01-05</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001024126</issuerCik>
        <issuerName>PERNIX THERAPEUTICS HOLDINGS, INC.</issuerName>
        <issuerTradingSymbol>PTX</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001607857</rptOwnerCik>
            <rptOwnerName>Pina Kenneth</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O PERNIX THERAPEUTICS HOLDINGS, INC.</rptOwnerStreet1>
            <rptOwnerStreet2>10 NORTH PARK PLACE, SUITE 201</rptOwnerStreet2>
            <rptOwnerCity>MORRISTOWN</rptOwnerCity>
            <rptOwnerState>NJ</rptOwnerState>
            <rptOwnerZipCode>07960</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>SVP, GC &amp; Compliance  Off.</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2018-01-05</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>F</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>446</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>2.74</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>15554</value>
                    <footnoteId id="F2"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">No shares were sold - these shares were withheld by the Issuer to satisfy tax withholding requirements in connection with the insider's exercise of his withholding right following the vesting of restricted share units (&quot;RSUs&quot;).</footnote>
        <footnote id="F2">Consists of (i) 804 shares of common stock, (ii) the unvested amount of previously awarded RSUs that vest in three equal installments of 1,250 shares, with the next installment vesting on January 5, 2019, (iii) the unvested amount of previously awarded RSUs that vest in four equal installments of 1,500 shares, with the next installment vesting on August 8, 2018 and (iv) the unvested amount of previously awarded RSUs that vest in four equal annual installments of 1,250, with the next installment vesting on March 15, 2019.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ Kenneth R. Pina</signatureName>
        <signatureDate>2018-04-09</signatureDate>
    </ownerSignature>
</ownershipDocument>
