AKORN, INC. COMMON STOCK PURCHASE WARRANT To Purchase 2,099,935 Shares of Common Stock

Exhibit 10.4

EXECUTION COPY

THIS SECURITY AND THE SECURITIES INTO WHICH THIS SECURITY IS EXERCISABLE HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED (THE “ SECURITIES ACT ”), OR THE SECURITIES LAWS OF ANY STATE OR OTHER JURISDICTION IN RELIANCE UPON AN EXEMPTION FROM REGISTRATION UNDER THE SECURITIES ACT, AND, ACCORDINGLY, MAY NOT BE OFFERED, SOLD OR OTHERWISE TRANSFERRED EXCEPT (1) PURSUANT TO AN EXEMPTION FROM REGISTRATION UNDER THE SECURITIES ACT OR (2) PURSUANT TO AN EFFECTIVE REGISTRATION STATEMENT UNDER THE SECURITIES ACT, IN EACH CASE IN ACCORDANCE WITH ALL APPLICABLE SECURITIES LAWS OF THE STATES AND OTHER JURISDICTIONS.

AKORN, INC.

COMMON STOCK PURCHASE WARRANT

To Purchase 2,099,935 Shares of Common Stock

     THIS COMMON STOCK PURCHASE WARRANT (this “ Warrant ”) certifies that, for value received, THE JOHN N. KAPOOR TRUST DATED SEPTEMBER 20, 1989 (the “ Holder ”), is entitled, upon the terms and subject to the limitations on exercise and the conditions hereinafter set forth, at any time on or after August 17, 2009 (the “ Initial Exercise Date ”) and on or prior to the close of business on the fifth (5th) anniversary following the Initial Exercise Date (the “ Termination Date ”) but not thereafter, to subscribe for and purchase from Akorn, Inc., a Louisiana corporation (the “ Company ”), up to Two Million Ninety-Nine Thousand Nine Hundred Thirty-Five (2,099,935) shares, subject to adjustment as set forth herein (the “ Warrant Shares ”) of Common Stock, no par value per share, of the Company (the “ Common Stock ”). The purchase price of one share of Common Stock (the “ Exercise Price ”) under this Warrant shall be $1.16 per share, subject to adjustment hereunder. The Exercise Price and the number of Warrant Shares for which the Warrant is exercisable shall be subject to adjustment as provided herein. Capitalized terms used and not otherwise defined herein shall have the meanings set forth in that certain Registration Rights Agreement (the “ Registration Rights Agreement ”), dated as of August 17, 2009, between the Company and Holder.

     Concurrently with the issuance of this Warrant, the Holder is entering into an Amended and Restated Subordination Agreement dated as of August 17, 2009 (the “ Amended Subordination Agreement ”), pursuant to which the Holder is providing certain financial accommodations to the Company as described therein, and this Warrant is being issued to Holder as partial consideration therefor.

     1.  Title to Warrant . Prior to the Termination Date and subject to compliance with applicable laws and Section 7 hereof, this Warrant and all rights hereunder are transferable, in whole or in part, at the office or agency of the Company by the Holder in person or by duly authorized attorney, upon surrender of this Warrant together with the Assignment Form annexed hereto properly endorsed. The transferee shall sign an investment letter in form and substance reasonably satisfactory to the Company.

     2.  Authorization of Shares . The Company covenants that all Warrant Shares which may be issued upon any Exercise of the purchase rights represented by this Warrant will, upon such Exercise in accordance with the terms of this Warrant, be duly authorized, validly issued, fully paid and nonassessable and free from all taxes, liens and charges in respect of the issue thereof (other than taxes in respect of any transfer occurring contemporaneously with such issue). The Company shall at all times reserve and keep available for issue upon the Exercise of this Warrant such number of shares of its authorized but unissued Common Stock as will be sufficient to permit the Exercise in full of this Warrant.

     3.  Exercise of Warrant .

          (a) Exercise of the purchase rights represented by this Warrant may be made at any time or times on or after the Initial Exercise Date and on or before the Termination Date by the surrender of this Warrant and the Notice of Exercise annexed hereto duly executed, at the office of the Company (or such other office or agency of the Company as it may designate by notice in writing to the registered Holder at the address of such Holder appearing on the books of the Company) to the attention of the Chief Executive Officer or the Chief Financial Officer (the “ Exercise ”, and the date of such Exercise, the “ Exercise Date ”). After each Exercise and upon the occurrence of the Exercise Effectiveness Date (as hereinafter defined), the Holder shall immediately thereafter

be entitled to receive a certificate for the number of Warrant Shares so purchased upon payment of the Exercise Price of the shares thereby purchased. Payment of the Exercise Price may be made at the option of the Holder by (i) by wire transfer or cashier’s check drawn on a United States bank of United States dollars or (ii) the surrender and cancellation of Warrant Shares issuable upon such Exercise of this Warrant (i.e. on a “cashless exercise” basis), in which event the Company shall issue to the Holder a number of shares of Common Stock computed using the following formula:

     X = The net number of shares of Common Stock to be issued to the Holder pursuant to the election to exercise;

     Y = The gross number of shares of Common Stock in respect of which the election to exercise is made;

     A = The average of the market price of one share of the Common Stock for the ten (10) Trading Days immediately prior to the Exercise Date; and

     B = The Exercise Price.

“ Market Price ” shall mean the closing sale price of the Company’s Common Stock as reported on the Nasdaq Global Market, or if not then traded on the Nasdaq Global Market, such closing sale or bid price as reported on any exchange over which the Company’s Common Stock may then be traded, or if not then traded over any exchange, then the market price of the Company’s Common Stock shall be the fair market value of the Company’s Common Stock as determined in good faith by the Board of Directors of the Company. Certificates for shares purchased hereunder shall be delivered to the Holder (at an address in the United States specified by the Holder) within five (5) Trading Days after the later of the Exercise Effectiveness Date and payment of the Exercise Price of the shares thereby purchased as aforesaid or the Company shall instruct its transfer agent to register the shares purchased hereunder in book entry form within five (5) Trading Days after the later of the Exercise Effectiveness Date and payment of the Exercise Price of the shares thereby purchased as aforesaid. This Warrant shall be deemed to have been exercised and such certificate or certificates (or book entry shares) shall be deemed to have been issued, and the Holder or any other person so designated to be named therein shall be deemed to have become a holder of record of such shares for all purposes, as of the last to occur of the Exercise Effectiveness Date, payment of the Exercise Price, and delivery of the required documentation and all taxes required to be paid by the Holder, if any, pursuant to Section 5 . For purposes of this Warrant, a “ Trading Day ” shall mean any day on which the national securities exchange or the national market system of FINRA are open for trading.

          (b) If this Warrant shall have been exercised in part, the Company shall, at the time of delivery of the certificate or certificates representing Warrant Shares, deliver to the Holder a new Warrant evidencing the rights of the Holder to purchase the unpurchased Warrant Shares called for by this Warrant, which new Warrant shall in all other respects be identical with this Warrant.

          (c) The Holder understands that, until such time as the Registration Statement has been declared effective or the Warrant Shares may be sold pursuant to Rule 144 under the Securities Act without any restriction as to the number of securities as of a particular date that can then be immediately sold, (i) the Company shall be entitled to give its transfer agent stop transfer instructions respecting those Warrant Shares and (ii) the certificates representing any Warrants Shares issued upon Exercise of this Warrant will bear a restrictive legend in substantially the following form:

“THE SECURITIES EVIDENCED BY THIS CERTIFICATE HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED (THE “ SECURITIES ACT ”) OR THE SECURITIES LAWS OF ANY STATE OR OTHER JURISDICTION. THE SECURITIES MAY NOT BE OFFERED, SOLD OR OTHERWISE TRANSFERRED EXCEPT (1) PURSUANT TO AN EXEMPTION FROM REGISTRATION UNDER THE SECURITIES ACT OR (2) PURSUANT TO AN EFFECTIVE REGISTRATION STATEMENT UNDER THE SECURITIES ACT, IN EACH CASE IN ACCORDANCE WITH ALL APPLICABLE SECURITIES LAWS OF THE STATES AND OTHER JURISDICTIONS, AND IN THE CASE OF A TRANSACTION EXEMPT FROM REGISTRATION, UNLESS THE COMPANY HAS RECEIVED AN

OPINION OF COUNSEL REASONABLY SATISFACTORY TO IT THAT SUCH TRANSACTION DOES NOT REQUIRE REGISTRATION UNDER THE SECURITIES ACT AND SUCH OTHER APPLICABLE LAWS.”

          (d) Reporting and Waiting Requirements .

               (i) To the extent necessary, each of and the Company and the Holder shall file, within fifteen (15) days after each Exercise Date, before the expiration of any relevant legal deadline, with (i) the FTC and the Antitrust Division of the DOJ, a Notification and Report Form required under the HSR Act with respect to the transactions contemplated pursuant to such Exercise and any supplemental information requested in connection therewith pursuant to the HSR Act, which forms shall specifically request early termination of the waiting period prescribed by the HSR Act and (ii) any other Governmental Authority, any other filings, reports, information and documentation required for the transactions contemplated hereby pursuant to any other antitrust law of any other jurisdiction. The parties shall furnish to each other’s counsel such necessary information and reasonable assistance as the other may reasonably request in connection with its preparation of any filing or submission that is necessary under the HSR Act and any antitrust law of any other jurisdiction. The requirements under this Section 3(d)(i) shall be satisfied with respect to any Exercise (without the need for further action by a party) upon the soonest to occur of: (a) the HSR Clearance Date has occurred (provided, however, that rights obtained by the Holder pursuant to the Warrant outside the United States shall become effective upon the HSR Clearance Date or, if any ex-U.S. governmental or regulatory approvals are required prior to such rights becoming effective, upon the later to occur of (1) the HSR Clearance Date and (2) the receipt of any such required approvals), or (b) determination by the parties that such filings are unnecessary (with respect to such Exercise, the “ Exercise Effectiveness Date ”). The determination of the soonest to occur of the foregoing shall be made without taking into account the need for ex-U.S. governmental or regulatory approvals required prior to such rights becoming effective and if, giving effect to the foregoing, subsection (a) is the soonest to occur, then the Exercise Effectiveness Date shall be the HSR Clearance Date.

               (ii) The parties shall use their reasonable best efforts to promptly obtain any clearance required under the HSR Act and any other antitrust law for the consummation of the Exercise and the transactions contemplated thereby and shall keep each other apprised of the status of any communications with, and any inquiries or requests for additional information from, the FTC and the DOJ and other Governmental Authorities concerning such clearances and shall use reasonable best efforts to comply promptly with any such inquiry or request; provided, however, that (a) neither party shall be required to consent to the divestiture or other disposition of any of its or its affiliates’ assets or those of the other party, or to agree to any modification or amendment of this Warrant that, in the reasonable opinion of such party’s legal and/or financial counsel, would be adverse to such party, and (b) neither party shall have any obligation to contest, administratively or in court, any ruling, order or other action of any Governmental Authority or private party respecting the transactions contemplated by this Warrant or to comply with any other structure or conduct remedy or restriction or limit on operation; provided, further, however, that the parties shall both promptly respond to the DOJ or the FTC to a request for additional information as defined under the HSR Act.

               (iii) The parties commit to instruct their respective counsel to cooperate with each other and use reasonable best efforts to facilitate and expedite the identification and resolution of any such issues and, consequently, the expiration of the applicable HSR Act waiting period and the waiting periods under any other antitrust law of any other jurisdiction, or the obtaining of clearances thereunder (as the case may be), at the earliest practicable dates. Such efforts and cooperation include, but are not limited to, the parties’ respective counsel undertaking (i) to keep each other appropriately informed of communications from and to personnel of the reviewing antitrust authority, and (ii) to confer with each other regarding appropriate contacts with and response to personnel of said antitrust authority.

               (iv) Each Party shall be responsible for its own costs and expenses associated with any filing under the HSR Act or the Law of any other jurisdiction.

               (v) Certain Terms. As used in this Section 3(d) , the below terms shall have the meanings so specified.

                    (1) “ DOJ ” shall mean the United States Department of Justice.