Exhibit 99.1

ALKERMES PLC REPORTS FINANCIAL RESULTS FOR FISCAL YEAR 2013 AND PROVIDES FINANCIAL EXPECTATIONS

— Fiscal Year 2013 Revenues Grew 48% Year-Over-Year to $575.5 Million —

— Fiscal Year 2013 Non-GAAP EPS Grew to $1.31 From $0.34 in the Prior Year —

— Announces Change in Fiscal Year-End From March 31 to Dec. 31 —

DUBLIN, Ireland, May 23, 2013 — Alkermes plc (NASDAQ: ALKS) today reported financial results for its fourth quarter and fiscal year ended March 31, 2013. The company also announced that it has changed its fiscal year-end from March 31 to Dec. 31, and provided financial expectations for the nine-month period ending Dec. 31, 2013.

“This was a remarkable year characterized by robust revenue growth, focused investment and significant cash flows. Our portfolio of five key commercial products is growing and generating significant revenues that provide the financial foundation of the company. For the remainder of calendar 2013, we expect our portfolio of five key products to grow approximately 25% year-over-year,” commented James Frates, Chief Financial Officer of Alkermes. “We are committed to managing our business to create value by generating significant cash flows while fueling future growth by investing in our valuable late-stage pipeline.”

Highlights for Quarter Ended March 31, 2013

·                  Total revenues for the quarter were $163.4 million and included $30.0 million of intellectual property license revenue unrelated to key development programs. This compared to total revenues of $130.5 million for the same period in the prior fiscal year.

·                  Revenues from the company’s five key commercial products for the quarter grew 26% to $89.5 million from $71.2 million for the same period in the prior fiscal year.

·                  Non-GAAP net income increased to $56.3 million, or a non-GAAP diluted earnings per share (EPS) of $0.40, for the quarter. This compared to non-GAAP net income of $16.5 million, or a non-GAAP diluted EPS of $0.12, for the same period in the prior fiscal year.

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·                  GAAP net income increased to $3.0 million, or a basic and diluted GAAP EPS of $0.02, for the quarter. This compared to a GAAP net loss of $63.4 million, or a basic and diluted GAAP net loss per share of $0.49, for the same period in the prior fiscal year.

·                  Free cash flow increased to $48.0 million for the quarter compared to $8.4 million for the same period in the prior fiscal year.

Highlights for Fiscal Year Ended March 31, 2013

·                  Total revenues increased 48% to $575.5 million, reflecting the first full fiscal year following the completion of the merger of Alkermes, Inc. with Elan Drug Technologies (EDT) on Sept. 16, 2011. Fiscal 2013 total revenues included $50.0 million of intellectual property license revenue unrelated to key development programs. This compared to total revenues of $390.0 million for the prior fiscal year.

·                  Non-GAAP net income increased to $179.5 million, or a non-GAAP diluted EPS of $1.31, for fiscal 2013. This compared to non-GAAP net income of $40.0 million, or a non-GAAP diluted EPS of $0.34, for the prior fiscal year.

·                  GAAP net income increased to $25.0 million, or a basic GAAP EPS of $0.19 and a diluted GAAP EPS of $0.18, for fiscal 2013. This compared to a GAAP net loss of $113.7 million, or a basic and diluted GAAP net loss per share of $0.99, for the prior fiscal year.

·                  Free cash flow increased to $157.3 million for fiscal 2013 compared to $23.0 million for the prior fiscal year.

“Our financial results reported today reflect the financial transformation of Alkermes. Our business is now evolving to the next stage as our pipeline of highly differentiated candidates advances and demonstrates its blockbuster potential,” commented Richard Pops, Chief Executive Officer of Alkermes. “Our recent pipeline progress validates Alkermes’ strategy to identify and develop new medicines that address critical unmet needs for patients suffering from major chronic CNS diseases. This year marks a significant inflection point for Alkermes as our clinical candidates advance across all stages of the pipeline.”

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Financial Results for Fiscal Year Ended March 31, 2013

Revenues

·                  Manufacturing and royalty revenues from the company’s long-acting atypical antipsychotic franchise, RISPERDAL® CONSTA® and INVEGA® SUSTENNA®/XEPLION®, were $197.0 million, compared to $186.3 million for fiscal 2012.

·                  Manufacturing and royalty revenues from AMPYRA®/FAMPYRA®(1) were $65.0 million, compared to $24.6 million for fiscal 2012.

·                  Net sales of VIVITROL® were $58.1 million, compared to $41.2 million for fiscal 2012, representing an increase of approximately 41% year-over-year.

·                  Royalty revenue from BYDUREON® was $16.4 million, compared to $1.5 million for fiscal 2012.

·                  Additionally, fiscal 2013 results included RITALIN LA®/FOCALIN XR® revenues of $40.3 million, TRICOR® 145 revenues of $37.5 million and VERELAN® revenues of $23.8 million. This compared to RITALIN LA/FOCALIN XR revenues of $23.1 million, TRICOR 145 revenues of $27.8 million and VERELAN revenues of $14.2 million for fiscal 2012.

·                  Manufacturing and royalty revenues in fiscal 2013 also included $50.0 million of intellectual property license revenue unrelated to key development programs.

Costs and Expenses

·                  Operating expenses for fiscal 2013 were $493.7 million, which included $12.3 million in one-time restructuring charges related to the Athlone, Ireland manufacturing facility. This compared to operating expenses of $478.3 million for fiscal 2012.

·                  Net interest expense for fiscal 2013 was $48.2 million, including one-time charges of $19.7 million related to the refinancing and repricing of term loans secured to fund the acquisition of EDT. This compared to net interest expense of $26.6 million for fiscal 2012.

Balance Sheet

At March 31, 2013, Alkermes recorded cash and total investments of $304.2 million, reflecting an increase of $64.9 million from $239.3 million at Dec. 31, 2012. During the year ended March 31, 2013, Alkermes reduced its overall debt outstanding by $75 million to $375 million, and reduced the blended interest rate from approximately 7.6% to approximately 3.4%.

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Financial Expectations for Nine Months Ending December 31, 2013

Alkermes has changed its fiscal year-end from March 31 to Dec. 31. The following outlines Alkermes’ financial expectations for the nine-month period ending Dec. 31, 2013. The following statements are forward-looking, and actual results may differ materially. Please see “Note Regarding Forward-Looking Statements” at the end of this press release for risks that could cause results to differ materially from these forward-looking statements.

·                  Revenues: Alkermes expects total revenues to range from $395 million to $425 million, for the nine months ending Dec. 31, 2013. Included in this total revenue expectation, Alkermes expects VIVITROL net sales to range from $50 million to $60 million.

·                  Cost of Goods Manufactured: The company expects cost of goods manufactured to range from $130 million to $140 million.

·                  Research and Development (R&D) Expenses: The company expects R&D expenses to range from $125 million to $135 million.

·                  Selling, General and Administrative (SG&A) Expenses: The company expects SG&A expenses to range from $95 million to $105 million.

·                  Amortization of Intangible Assets: The company expects amortization of intangibles to be approximately $40 million.

·                  Net Interest Expense: The company expects net interest expense to be approximately $10 million.

·                  Net Income Tax Expense: The company expects net income tax expense to range from $5 million to $10 million.

·                  GAAP Net Loss: The company expects a GAAP net loss in the range of breakeven to a loss of $25 million, or a basic and diluted EPS of $0 to a basic and diluted loss per share of approximately $0.19, based on a weighted average basic and diluted share count of approximately 135 million shares outstanding.

·                  Non-GAAP Net Income: The company expects non-GAAP net income to range from $85 million to $105 million, and non-GAAP diluted EPS to range from $0.61 to $0.75, based on a weighted average diluted share count of approximately 140 million shares outstanding.

·                  Capital Expenditures: The company expects capital expenditures to be approximately $20 million.

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·                  Free Cash Flow: The company expects free cash flow to range from $65 million to $85 million.

Following the change in the company’s financial year-end, the company expects total pro forma revenues for the calendar year ending Dec. 31, 2013, to range from $558 million to $588 million. This compares to total pro forma total revenues of $542.6 million for the calendar year ended Dec. 31, 2012. The company also expects pro forma non-GAAP net income for the calendar year ending Dec. 31, 2013, to range from $141 million to $161 million. This compares to pro forma non-GAAP net income of $139.7 million for the calendar year ended Dec. 31, 2012. A workbook with historical pro forma results by calendar year and nine-month period ending Dec. 31 is available in the Investors section of the company’s website at www.alkermes.com.

Conference Call

Alkermes will host a conference call at 8:00 a.m. EDT (1:00 p.m. BST) on Thursday, May 23, 2013, to discuss these financial results and provide an update on the company. The conference call may be accessed by dialing +1 888 424 8151 for U.S. callers and +1 847 585 4422 for international callers. The conference call ID number is 6037988. In addition, a replay of the conference call will be available from 10:30 a.m. EDT (3:30 p.m. BST) on Thursday, May 23, 2013, through 5:00 p.m. EDT (10:00 p.m. BST) on Thursday, May 30, 2013, and may be accessed by visiting Alkermes’ website or by dialing +1 888 843 7419 for U.S. callers and +1 630 652 3042 for international callers. The replay access code is 6037988.

About Alkermes plc

Alkermes plc is a fully integrated, global biopharmaceutical company that applies its scientific expertise and proprietary technologies to develop innovative medicines that improve patient outcomes. The company has a diversified portfolio of more than 20 commercial drug products and a substantial clinical pipeline of product candidates that address central nervous system (CNS) disorders such as addiction, schizophrenia and depression. Headquartered in Dublin, Ireland, Alkermes plc has an R&D center in Waltham, Massachusetts; a research and manufacturing facility in Athlone, Ireland; and manufacturing facilities in Gainesville, Georgia

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and Wilmington, Ohio. For more information, please visit Alkermes’ website at www.alkermes.com.

Non-GAAP Financial Measures

This press release includes information about certain financial measures that are not prepared in accordance with generally accepted accounting principles in the U.S. (GAAP), including non-GAAP net income, non-GAAP diluted earnings per share and free cash flow. These non-GAAP measures are not based on any standardized methodology prescribed by GAAP and are not necessarily comparable to similar measures presented by other companies.

Management defines its non-GAAP financial measures as follows:

·                              Non-GAAP net income adjusts for one-time and non-cash charges by excluding from GAAP results: share-based compensation expense; amortization; depreciation; non-cash net interest expense; non-cash tax expense; deferred revenue; and certain other one-time or non-cash items.

·                              Free cash flow represents non-GAAP net income less capital expenditures.

Management believes that these non-GAAP financial measures, when viewed with our results under GAAP and the accompanying reconciliations, better indicate underlying trends in ongoing operations and cash flows. However, non-GAAP net income, non-GAAP diluted earnings per share and free cash flow are not measures of financial performance under GAAP and, accordingly, should not be considered as alternatives to GAAP measures as indicators of operating performance.

A reconciliation of GAAP to non-GAAP financial measures has been provided in the tables included in this press release.

Note Regarding Forward-Looking Statements

Certain statements set forth above may constitute forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995, including, but not limited to: statements concerning future financial and operating performance, business plans or prospects; the likelihood of continued revenue growth from the company’s commercial products; the

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therapeutic and commercial value of the company’s products; and our expectations concerning the timing and results of our clinical development activities. These statements are neither promises nor guarantees and are subject to a variety of risks and uncertainties, many of which are beyond the company’s control, which could cause actual results to differ materially from those contemplated in these forward-looking statements.

These risks and uncertainties include, among others: whether clinical development activities will be completed on time or at all and whether the results of such activities will be predictive of real-world results or of results in subsequent clinical trials; whether the company, and its partners, are able to continue to successfully commercialize its products; whether there will be a reduction in payment rate or reimbursement for the company’s products or an increase in the company’s financial obligations to governmental payors; the possibility of adverse decisions by the U.S. Food and Drug Administration (FDA) or regulatory authorities outside the U.S. regarding the company’s products; the possibility that the company’s products may prove difficult to manufacture, be precluded from commercialization by the proprietary rights of third parties, or have unintended side effects, adverse reactions or incidents of misuse;  and those risks described in the company’s most recent Annual Report on Form 10-K, and in other filings made by the company with the Securities and Exchange Commission (“SEC”) and which are available at the SEC’s website at www.sec.gov. Existing and prospective investors are cautioned not to place undue reliance on these forward-looking statements, which speak only as of the date they are made. The information contained in this press release is provided by the company as of the date hereof and, except as required by law, the company disclaims any intention or responsibility for updating any forward-looking information contained in this press release.

VIVITROL® is a registered trademark of Alkermes, Inc.; RISPERDAL® CONSTA® and INVEGA® SUSTENNA® are registered trademarks of Janssen Pharmaceuticals, Inc.; XEPLION® is a registered trademark of Johnson & Johnson Corporation; AMPYRA® and FAMPYRA® are registered trademarks of Acorda Therapeutics, Inc.; BYDUREON® is a registered trademark of Amylin Pharmaceuticals, LLC; TRICOR® is a registered trademark of Fournier Industrie et Sante Corporation; and RITALIN LA® and FOCALIN XR® are registered trademarks of Novartis AG Corporation; and VERELAN® is a registered trademark of Alkermes Pharma Ireland Limited.

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(1)AMPYRA® (dalfampridine) Extended Release Tablets, 10 mg is developed and marketed in the U.S. by Acorda Therapeutics, Inc. and outside the U.S. by Biogen Idec, under a licensing agreement with Acorda Therapeutics, as FAMPYRA® (prolonged-release fampridine tablets).

 (tables follow)

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Alkermes plc and Subsidiaries

Selected Financial Information (Unaudited)

Alkermes plc and Subsidiaries

Selected Financial Information (Unaudited)

Alkermes plc and Subsidiaries

Selected Financial Information (Unaudited)

This selected financial information should be read in conjunction with the consolidated financial statements and notes thereto included in Alkermes plc’s Annual Report on Form 10-K for the year ended March 31, 2013, which the company intends to file in May 2013.

Alkermes plc and Subsidiaries

Guidance — GAAP to Non-GAAP Adjustments

An itemized reconciliation between projected loss per share on a GAAP basis and projected earnings per share

on a non-GAAP basis is as follows:

Projected GAAP and non-GAAP measures reflect mid-points within ranges of estimated guidance.