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

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2004-11-10</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000003116</issuerCik>
        <issuerName>AKORN INC</issuerName>
        <issuerTradingSymbol>AKRN.OB</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001267367</rptOwnerCik>
            <rptOwnerName>WANEY GULU CHAINRAI</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>VILLA 11, OFF AL TRANY STREET</rptOwnerStreet1>
            <rptOwnerStreet2>UMM SUQUEIM, P.O. BOX 53078</rptOwnerStreet2>
            <rptOwnerCity>DUBAI, U.A.E.</rptOwnerCity>
            <rptOwnerState></rptOwnerState>
            <rptOwnerZipCode></rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2004-11-10</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>X</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>99578</value>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F1"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>624773</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Stock Purchase Warrant</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>1.00</value>
                <footnoteId id="F2"/>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2004-11-10</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>X</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>133333</value>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F3"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2004-11-10</value>
            </exerciseDate>
            <expirationDate>
                <value>2006-10-07</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>99578</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>200000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
        <derivativeTransaction>
            <securityTitle>
                <value>Series A Preferred</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>0.75</value>
                <footnoteId id="F2"/>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2004-09-30</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>J</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F4"/>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionTotalValue>
                    <value>15670</value>
                </transactionTotalValue>
                <transactionPricePerShare>
                    <footnoteId id="F4"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2004-09-30</value>
            </exerciseDate>
            <expirationDate>
                <value>2011-10-31</value>
                <footnoteId id="F5"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>20893</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <valueOwnedFollowingTransaction>
                    <value>1060317</value>
                </valueOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">The reporting person exercised 133,333 of the Series A Preferred Stock Warrants (the &quot;Warrants&quot;) on November 10, 2004 at an exercise price equal to $1.00 per share (subject to adjustment), resulting in his acquisition of 99,578 shares of common stock. Each Warrant represents the right to acquire one share of common stock; however, the reporting person exercised the warrants on a cashless exercise basis thereby reducing the number of shares of common stock acquirable upon the exercise of such Warrant, as provided for in the Warrant Agreement dated as of October 7, 2003.</footnote>
        <footnote id="F2">Subject to adjustment.</footnote>
        <footnote id="F3">The reporting person exercised 133,333 of the Series A Preferred Stock Warrants (the &quot;Warrants&quot;) on November 10, 2004 at an exercise price equal to $1.00 per share (subject to adjustment), resulting in his acquisition of 99,578 shares of common stock. Each Warrant represents the right to acquire one share of common stock; however, the reporting person exercised the warrants on a cashless exercise basis thereby reducing the number of shares of common stock acquirable upon the exercise of such Warrant, as provided for in the Warrant Agreement dated as of October 7, 2003.</footnote>
        <footnote id="F4">Dividend resulting from existing Series A 6% Participating Convertible Preferred Stock ownership.</footnote>
        <footnote id="F5">Mandatory redemption on this date.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/Gulu C. Waney/</signatureName>
        <signatureDate>2004-11-12</signatureDate>
    </ownerSignature>
</ownershipDocument>

