SCHEDULE 13G Amendment No. 3 HORIZON PHARMA INC Common Stock Cusip #44047T109 Cusip #44047T109 Item 1: Reporting Person - FMR LLC Item 4: Delaware Item 5: 383,835 Item 6: 0 Item 7: 8,895,482 Item 8: 0 Item 9: 8,895,482 Item 11: 14.986% Item 12: HC Cusip #44047T109 Item 1: Reporting Person - Edward C. Johnson 3d Item 4: United States of America Item 5: 0 Item 6: 0 Item 7: 8,895,482 Item 8: 0 Item 9: 8,895,482 Item 11: 14.986% Item 12: IN SCHEDULE 13G - TO BE INCLUDED IN STATEMENTS FILED PURSUANT TO RULE 13d-1(b) or 13d-2(b) Item 1(a). Name of Issuer: HORIZON PHARMA INC Item 1(b). Name of Issuer's Principal Executive Offices: 520 Lake Cook Road Suite 520 Deerfield, IL 60062 Item 2(a). Name of Person Filing: FMR LLC Item 2(b). Address or Principal Business Office or, if None, Residence: 82 Devonshire Street, Boston, Massachusetts 02109 Item 2(c). Citizenship: Not applicable Item 2(d). Title of Class of Securities: Common Stock Item 2(e). CUSIP Number: 44047T109 Item 3. This statement is filed pursuant to Rule 13d-1(b) or 13d-2(b) and the person filing, FMR LLC, is a parent holding company in accordance with Section 240.13d-1(b)(ii)(G). (Note: See Item 7). Item 4. Ownership (a) Amount Beneficially Owned: 8,895,482 (b) Percent of Class: 14.986% (c) Number of shares as to which such person has: (i) sole power to vote or to direct the vote: 383,835 (ii) shared power to vote or to direct the vote: 0 (iii) sole power to dispose or to direct the disposition of: 8,895,482 (iv) shared power to dispose or to direct the disposition of: 0 Item 5. Ownership of Five Percent or Less of a Class. Not applicable. Item 6. Ownership of More than Five Percent on Behalf of Another Person. Various persons have the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of, the Common Stock of HORIZON PHARMA INC. The interest of one person, Fidelity Dividend Growth Fund, an investment company registered under the Investment Company Act of 1940, in the Common Stock of HORIZON PHARMA INC, amounted to 4,382,408 shares or 7.383% of the total outstanding Common Stock at September 30, 2012. Item 7. Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on By the Parent Holding Company. See attached Exhibit A. Item 8. Identification and Classification of Members of the Group. Not applicable. See attached Exhibit A. Item 9. Notice of Dissolution of Group. Not applicable. Item 10. Certification. By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were acquired in the ordinary course of business and were not acquired for the purpose of and do not have the effect of changing or influencing the control of the issuer of such securities and were not acquired in connection with or as a participant in any transaction having such purpose or effect. Signature After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct. October 09, 2012 Date /s/ Scott C. Goebel Signature Scott C. Goebel Duly authorized under Power of Attorney effective as of June 1, 2008 by and on behalf of FMR LLC and its direct and indirect subsidiaries SCHEDULE 13G - TO BE INCLUDED IN STATEMENTS FILED PURSUANT TO RULE 13d-1(b) or 13d-2(b) Pursuant to the instructions in Item 7 of Schedule 13G, Fidelity Management & Research Company ("Fidelity"), 82 Devonshire Street, Boston, Massachusetts 02109, a wholly- owned subsidiary of FMR LLC and an investment adviser registered under Section 203 of the Investment Advisers Act of 1940, is the beneficial owner of 8,511,647 shares or 14.340% of the Common Stock outstanding of HORIZON PHARMA INC ("the Company") as a result of acting as investment adviser to various investment companies registered under Section 8 of the Investment Company Act of 1940. The number of shares of Common Stock of HORIZON PHARMA INC owned by the investment companies at September 30, 2012 included 0 shares of Common Stock resulting from the assumed conversion of 0 shares of HORIZON PHARMA(1CS+.5WT)UNITS (0.5 shares of Common Stock for each Unit Stock). The number of shares of Common Stock of HORIZON PHARMA INC owned by the investment companies at September 30, 2012 included 2,039,337 shares of Common Stock resulting from the assumed conversion of 2,020,600 shares of HORIZON PHARMA WT (1 shares of Common Stock for each Warrant). The ownership of one investment company, Fidelity Dividend Growth Fund, amounted to 4,382,408 shares or 7.383% of the Common Stock outstanding. Fidelity Dividend Growth Fund has its principal business office at 82 Devonshire Street, Boston, Massachusetts 02109. Edward C. Johnson 3d and FMR LLC, through its control of Fidelity, and the funds each has sole power to dispose of the 8,511,647 shares owned by the Funds. Members of the family of Edward C. Johnson 3d, Chairman of FMR LLC, are the predominant owners, directly or through trusts, of Series B voting common shares of FMR LLC, representing 49% of the voting power of FMR LLC. The Johnson family group and all other Series B shareholders have entered into a shareholders' voting agreement under which all Series B voting common shares will be voted in accordance with the majority vote of Series B voting common shares. Accordingly, through their ownership of voting common shares and the execution of the shareholders' voting agreement, members of the Johnson family may be deemed, under the Investment Company Act of 1940, to form a controlling group with respect to FMR LLC. Neither FMR LLC nor Edward C. Johnson 3d, Chairman of FMR LLC, has the sole power to vote or direct the voting of the shares owned directly by the Fidelity Funds, which power resides with the Funds' Boards of Trustees. Fidelity carries out the voting of the shares under written guidelines established by the Funds' Boards of Trustees. Pyramis Global Advisors Trust Company ("PGATC"), 900 Salem Street, Smithfield, Rhode Island, 02917, an indirect wholly-owned subsidiary of FMR LLC and a bank as defined in Section 3(a)(6) of the Securities Exchange Act of 1934, is the beneficial owner of 383,835 shares or 0.647% of the outstanding Common Stock of the HORIZON PHARMA INC as a result of its serving as investment manager of institutional accounts owning such shares. The number of shares of Common Stock of HORIZON PHARMA INC owned by the institutional account(s) at September 30, 2012 included 79,400 shares of Common Stock resulting from the assumed conversion of 79,400 shares of HORIZON PHARMA WT (1 shares of Common Stock for each Warrant). Edward C. Johnson 3d and FMR LLC, through its control of Pyramis Global Advisors Trust Company, each has sole dispositive power over 383,835 shares and sole power to vote or to direct the voting of 383,835 shares of Common Stock owned by the institutional accounts managed by PGATC as reported above. SCHEDULE 13G - TO BE INCLUDED IN STATEMENTS FILED PURSUANT TO RULE 13d-1(b) or 13d-2(b) RULE 13d-1(f)(1) AGREEMENT The undersigned persons, on October 09, 2012, agree and consent to the joint filing on their behalf of this Schedule 13G in connection with their beneficial ownership of the Common Stock of HORIZON PHARMA INC at September 30, 2012. FMR LLC By /s/ Scott C. Goebel Scott C. Goebel Duly authorized under Power of Attorney effective as of June 1, 2008, by and on behalf of FMR LLC and its direct and indirect subsidiaries Edward C. Johnson 3d By /s/ Scott C. Goebel Scott C. Goebel Duly authorized under Power of Attorney effective as of June 1, 2008, by and on behalf of Edward C. Johnson 3d Fidelity Management & Research Company By /s/ Scott C. Goebel Scott C. Goebel Senior V.P. and General Counsel Fidelity Dividend Growth Fund By /s/ Scott C. Goebel Scott C. Goebel Secretary