Exhibit 99.1

Horizon Pharma Reports Fourth Quarter and Full Year 2011 Financial Results

DEERFIELD, IL. – March 23, 2012 – Horizon Pharma, Inc. (NASDAQ: HZNP) today reported financial results for the fourth quarter and year ended December 31, 2011, and provided an update on recent accomplishments by the Company. The Company ended the year with cash and cash equivalents totaling $18.0 million. Subsequent to the end of the year, in February and March 2012, the Company completed debt and equity offerings raising combined gross proceeds of $110.8 million and net proceeds of $81.7 million after paying fees and repaying outstanding amounts under previous debt facilities. As a result, as of March 16, 2012, the Company had $82.5 million in cash and cash equivalents.

For the year ended December 31, 2011, total revenues increased $4.6 million to $6.9 million compared to the prior year. Net loss for the year ended December 31, 2011, was $113.3 million, or $12.56 per share, compared to a net loss of $27.1 million, or $21.16 per share, in the prior year, with the increase in net loss largely due to a $69.6 million intangible impairment charge recorded during the fourth quarter of 2011 resulting primarily from the decline in the Company’s stock price in that period. Excluding the intangible impairment charge and certain other non-cash expenses, non-GAAP net loss for the year ended December 31, 2011, was $48.5 million, or $5.38 per share, compared to non-GAAP net loss of $39.8 million, or $31.13 per share in the prior year. Horizon provides non-GAAP financial measures, which it believes can enhance an overall understanding of Horizon’s financial performance when considered together with GAAP figures. Refer to the section of this press release below entitled “Note Regarding Use of Non-GAAP Financial Measures” for a full discussion on this subject.

“Since completing our IPO in August of last year, we have transformed the Company into a commercially focused biopharmaceutical organization,” said Timothy P. Walbert, chairman, president and chief executive officer, Horizon Pharma. “We completed the hiring and deployment of the initial stage of our commercial organization and began product shipments of DUEXIS in December. Furthermore, we completed a $60.0 million debt financing and a $50.8 million private equity offering in February and March 2012 to provide the Company with additional capital required to fund the ongoing commercial launch of DUEXIS in the U.S. and to pursue regulatory approval for RAYOS in the U.S. and DUEXIS in Europe.”

Recent Accomplishments

Fourth Quarter 2011 Financial Results

During the three months ended December 31, 2011, revenues increased $3.5 million compared to the same period in the prior year. The significant increase in revenues in the fourth quarter of 2011 was primarily the result of $2.1 million in higher product sales of LODOTRA in Europe in addition to the recognition of $1.2 million in deferred revenues associated with our distribution agreements.

Cost of goods sold increased $0.7 million during the three months ended December 31, 2011, compared to the same period in 2010, primarily as a result of higher product shipments of LODOTRA.

Research and development expenses decreased $1.0 million during the three months ended December 31, 2011, compared to the same period in 2010. The decrease was due to a reduction in our regulatory and clinical trial expenses, and a reduction in contract manufacturing in support of the regulatory approval of RAYOS.

Sales and marketing expenses increased $10.9 million during the three months ended December 31, 2011, compared to the same period in 2010. The increase was primarily due to hiring 80 field sales representatives and staffing our sales and marketing support functions during 2011, in addition to higher marketing costs associated with product launch and commercialization efforts for DUEXIS in the U.S.

General and administrative expenses decreased $0.1 million during the three months ended December 31, 2011, compared to the same period in 2010, primarily due to lower professional and consulting fees in the current year as a result of internal staffing of our administrative functions during 2011.

During the fourth quarter, the Company recorded an intangible impairment charge of $69.6 million related to its in-process research and development (IPR&D) asset, RAYOS. The Company reviews its intangible assets on an annual basis, or more frequently when events or circumstances may indicate that the carrying value of these assets exceeds its fair value. The Company evaluated its IPR&D asset in relation to its total business enterprise value as a result of the fourth quarter 2011 decline in the market value of the Company’s common stock. Accordingly, the Company recorded an intangible impairment charge of $69.6 million to reflect the fair value of the IPR&D as a component of the total business enterprise value.

Interest expense decreased $0.4 million during the three months ended December 31, 2011, compared to the same period in 2010, primarily as a result of the repayment of a prior debt facility in June 2011.

Foreign exchange loss increased $0.3 million for the three months ended December 31, 2011, compared to the same period in 2010, as a result of an increase in non-Euro denominated transactions for our Horizon Pharma AG subsidiary in addition to a strengthening of the U.S. dollar against the Euro in the fourth quarter of 2011.

Income tax benefit increased $13.4 million during the three months ended December 31, 2011, compared to the same period in 2010, as a result of a reduction in deferred tax assets associated with the IPR&D intangible impairment charge of $69.6 million.

Net loss for the fourth quarter of 2011 was $76.7 million, or $3.92 per share, compared to a net loss of $13.6 million, or $9.09 per share, in the fourth quarter of 2010. On a non-GAAP basis, after excluding the intangible impairment charge and certain other non-cash expenses, net loss for the fourth quarter of 2011 was $19.0 million, or $0.97 per share, compared to a net loss of $11.7 million, or $7.85 per share, in the fourth quarter of 2010.

Full Year 2011 Financial Results

During the year ended December 31, 2011, revenues increased $4.6 million compared to the prior year as a result higher product sales and the recognition of deferred revenues for LODOTRA in Europe. The Company also benefited from a full year of LODOTRA revenues in 2011 as compared to nine months in the prior year following our acquisition of Nitec Pharma AG in April 2010.

Cost of goods sold increased $3.0 million during the year ended December 31, 2011, compared to the prior year primarily as a result of higher LODOTRA sales and due to $1.1 million in additional amortization expense of our developed technology due to the inclusion of full year operating results of Horizon Pharma AG in 2011.

Research and development expenses decreased $2.3 million during the year ended December 31, 2011, compared to the prior year. The decrease was primarily due to a $2.1 million reduction in contract manufacturing and a $2.1 million reduction in regulatory expenses associated with RAYOS, which was partially offset by higher personnel costs of $1.7 million resulting from increased headcount to support DUEXIS development and regulatory activities, and DUEXIS post-marketing requirements.

Sales and Marketing expenses increased $14.8 million during the year ended December 31, 2011, compared to the prior year. The increase was attributable to hiring 80 field sales representatives and staffing our sales and marketing support functions during 2011, $3.2 million in commercialization expense related to the product launch of DUEXIS in December 2011, and $2.4 million in consulting and outside costs associated with pre-commercialization activities for DUEXIS in 2011 compared to the prior year.

General and administrative expenses decreased $3.6 million during the year ended December 31, 2011, compared to the prior year. The decrease in expenses was primarily the result of an approximately $2.3 million reduction in legal and professional fees associated with our acquisition of Nitech Pharma AG in April 2010 and a $1.5 million reduction in legal, consulting and audit related fees incurred during 2010 related to preparation for our initial public offering.

Interest expense increased $3.3 million during the year ended December 31, 2011, compared to the prior year. The increase was primarily due to a $1.9 million write-off of deferred financing fees as a result of the 2011 debt extinguishment in the current year and higher interest expense as a result of a higher borrowing base of debt as compared to the prior year.

Foreign exchange loss increased $0.8 million during the year ended December 31, 2011, compared to the prior year as a result of an increase in non-Euro denominated transactions for our Horizon Pharma AG subsidiary in addition to a strengthening of the U.S dollar against the Euro in 2011.

Horizon recorded a bargain purchase gain of $19.3 million during the year ended December 31, 2010, in connection with the Nitec Pharma AG acquisition resulting from the fair market value of the acquired tangible and intangible assets exceeding the purchase price. There was no similar bargain purchase gain recorded in 2011.

Income tax benefit increased $14.0 million during the year ended December 31, 2011, compared to the prior year as a result of a reduction in deferred tax assets associated with the IPR&D intangible impairment charge of $69.6 million recorded during the fourth quarter of 2011.

Net loss for the year ended December 31, 2011, was $113.3 million, or $12.56 per share, compared to a net loss of $27.1 million, or $21.16 per share, for the year ended December 31, 2010. On a non-GAAP basis, after excluding the bargain purchase gain in 2010, the intangible impairment charge in 2011, and certain other non-cash expenses during both 2010 and 2011, net loss for the year ended December 31, 2011, was $48.5 million, or $5.38 per share, compared to a net loss of $39.8 million, or $31.13 per share, for the year ended December 31, 2010.

Note Regarding Use of Non-GAAP Financial Measures

Horizon provides non-GAAP net income (loss) and net income (loss) per share financial measures that include adjustments to GAAP figures. These adjustments to GAAP involve the exclusion of non-cash items such as stock compensation and depreciation and amortization, and other charges such as the intangible impairment charge the Company recorded in the fourth quarter of 2011 related to its IPR&D asset and the bargain purchase gain the Company recorded in connection with its acquisition of Nitec Pharma AG in 2010. Horizon believes that these non-GAAP financial measures, when considered together with the GAAP figures, can enhance an overall understanding of Horizon’s financial performance. The non-GAAP financial measures are included with the intent of providing investors with a more complete understanding of operational results and trends. In addition, these non-GAAP financial measures are among the indicators Horizon management uses for planning and forecasting purposes and measuring the Company’s performance. These non-GAAP financial measures should be considered in addition to, and not as a substitute for, or superior to, financial measures calculated in accordance with GAAP. The non-GAAP financial measures used by the Company may be calculated differently from, and therefore may not be comparable to, non-GAAP financial measures used by other companies. Please refer to the financial statements portion of this press release for a reconciliation of these non-GAAP financial measures to the comparable GAAP financial measures.

About Horizon Pharma

Horizon Pharma, Inc. is a biopharmaceutical company that is developing and commercializing innovative medicines to target unmet therapeutic needs in arthritis, pain and inflammatory diseases. For more information, please visit www.horizonpharma.com.

Forward-Looking Statements

This press release contains forward-looking statements, including statements regarding the on-going commercial launch of DUEXIS and pursuit of regulatory approval for RAYOS in the U.S. and DUEXIS in Europe. These forward-looking statements are based on management’s expectations and assumptions as of the date of this press release, and actual results

may differ materially from those in these forward-looking statements as a result of various factors. These factors include, but are not limited to, risks regarding Horizon’s ability to commercialize products successfully, Horizon’s ability to continue to successfully recruit and retain sales and marketing personnel, and whether RAYOS and/or DUEXIS will be approved for marketing in the U.S. and Europe, respectively. For a further description of these and other risks facing the Company, please see the risk factors described in the Company’s filings with the United States Securities and Exchange Commission, including those factors discussed under the caption “Risk Factors” in those filings. Forward-looking statements speak only as of the date of this press release, and the Company undertakes no obligation to update or revise these statements, except as may be required by law.

Contacts

Robert J. De Vaere

Executive Vice President and Chief Financial Officer

investor-relations@horizonpharma.com

Media

Julie Normart

Invigorate PR

415-946-1087

jnormart@invigoratepr.com

Investors

Kathy Galante

Burns McClellan, Inc.

212-213-0006

kgalante@burnsmc.com

CONSOLIDATED BALANCE SHEETS

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CONSOLIDATED STATEMENTS OF OPERATIONS

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RECONCILIATION OF GAAP NET LOSS TO NON-GAAP NET LOSS

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CONSOLIDATED STATEMENTS OF CASH FLOWS

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