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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2013-04-30</periodOfReport>

    <issuer>
        <issuerCik>0000850693</issuerCik>
        <issuerName>ALLERGAN INC</issuerName>
        <issuerTradingSymbol>AGN</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001214127</rptOwnerCik>
            <rptOwnerName>LAVIGNE LOUIS J JR</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>2525 DUPONT DRIVE</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>IRVINE</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>92612</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2013-04-30</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>3102</value>
                    <footnoteId id="F1"/>
                    <footnoteId id="F2"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>12723</value>
                    <footnoteId id="F3"/>
                    <footnoteId id="F4"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>4800</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By Lavigne Survivor's Trust</value>
                    <footnoteId id="F5"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>5400</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By Rachel Lavigne Exmpt Bypass Trust</value>
                    <footnoteId id="F6"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Represents shares of the Issuer's common stock underlying RSUs awarded to the Reporting Person. The RSUs will vest in full upon the earlier to occur of (i) the first anniversary of the grant date, or (ii) the annual meeting during the calendar year following the grant date of the RSUs at which one or more members of the Issuer's board of directors is standing for re-election, provided the Reporting Person remains in the Issuer's service on such date.  The RSUs may vest earlier on an accelerated basis in the event of the Reporting Person's termination of service due to death or disability.</footnote>
        <footnote id="F2">The shares of the Issuer's common stock and underlying the RSUs will be issued to the reporting person no later than ten (10) businesses after the RSUs vest.</footnote>
        <footnote id="F3">Includes shares acquired pursuant to dividend equivalent rights attached to RSU previously granted to the Reporting Person.</footnote>
        <footnote id="F4">Includes 3,102 shares of the Issuer's common stock underlying the RSUs awarded.</footnote>
        <footnote id="F5">Shares held by the Louis Lavigne Survivor's Trust.  Reporting Person is sole trustee of the Louis Lavigne Survivor's Trust.</footnote>
        <footnote id="F6">Shares held by the Rachel Lavigne Exmpt Bypass Trust.  Reporting Person is sole trustee of the Rachel Lavigne Exmpt Bypass Trust.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ Matthew J. Maletta, Attorney-In-Fact for Louis J. Lavigne, Jr.</signatureName>
        <signatureDate>2013-05-02</signatureDate>
    </ownerSignature>
</ownershipDocument>
