(ARNA) Announces Retirement of President and CEO

SAN DIEGO, Oct. 5, 2015  — Arena Pharmaceuticals, Inc. (NASDAQ: ARNA) today announced that, at the request of the Board of Directors, Jack Lief, Arena’s President and Chief Executive Officer, has retired from the company, including its Board of Directors. Dr. Harry F. Hixson, a director of Arena since 2004, has been appointed to serve as interim Chief Executive Officer and interim principal financial officer. Arena will immediately initiate a search for a new chief executive officer.

“I leave Arena proud of the accomplishments made by our employees in advancing healthcare and science,” said Mr. Lief. “I look forward to watching the company transition through its next phase of development.”

“Jack has contributed in many ways since co-founding Arena in 1997, including overseeing the approval and commercial launch of the company’s internally discovered and developed drug BELVIQ, and the development of a robust clinical stage pipeline and productive research platform,” said Dr. Hixson. “We thank Jack and wish him great success in his future endeavors.”

Arena also reported that it is conducting an ongoing evaluation of its programs and operations, and intends to provide details regarding its 2016 financial plan later this year.

Dr. Hixson served as the Chairman of the board of directors of Sequenom, Inc., a genomics company, from January 2003 to March 2015, and as its Chief Executive Officer from September 2009 to June 2014. He previously served as Chief Executive Officer of BrainCells Inc., a drug discovery and development company, from 2004 to 2005, as Chief Executive Officer of Elitra Pharmaceuticals Inc., a biopharmaceutical company, from 1998 to 2003, and in various management positions with Amgen Inc., a biopharmaceutical company, from 1985 to 1991, most recently as President and Chief Operating Officer. Dr. Hixson holds a B.S. in Chemical Engineering from Purdue University, an M.B.A. from the University of Chicago and a Ph.D. in Physical Biochemistry from Purdue University.

About Arena Pharmaceuticals

Arena embraces the challenge of improving health by seeking to bring innovative medicines targeting G protein-coupled receptors to patients. Arena’s focus is discovering, developing and commercializing drugs to address unmet medical needs, and BELVIQ® (lorcaserin HCl) is Arena’s first internally discovered drug approved for marketing. Arena’s US operations are located in San Diego, California, and its operations outside of the United States, including its commercial manufacturing facility, are located in Zofingen, Switzerland. For more information, visit Arena’s website at www.arenapharm.com.

Arena Pharmaceuticals^® and Arena^® are registered service marks of Arena Pharmaceuticals, Inc. BELVIQ^® is a registered trademark of Arena Pharmaceuticals GmbH.

Forward-Looking Statements

Certain statements in this press release are forward-looking statements that involve a number of risks and uncertainties. Such forward-looking statements include statements about searching for a new chief executive officer; Arena’s evaluating its programs and operations; Arena’s financial plan; embracing the challenge of improving health; seeking to bring innovative medicines to patients; and Arena’s focus, plans, goals, strategy, expectations, research and development programs, and ability to discover and develop compounds and commercialize drugs. For such statements, Arena claims the protection of the Private Securities Litigation Reform Act of 1995. Actual events or results may differ materially from Arena’s expectations. Factors that could cause actual results to differ materially from the forward-looking statements include, but are not limited to, the following: the timing and decisions relating to identifying a new chief executive officer, the ongoing evaluation of Arena’s programs and operations, and Arena’s 2016 financial plan, are uncertain; risks related to commercializing drugs, including regulatory, manufacturing, supply and marketing issues and the availability and use of BELVIQ or lorcaserin; cash and revenues generated from BELVIQ, including the impact of competition; the risk that Arena’s revenues are based in part on estimates, judgment and accounting policies, and incorrect estimates or disagreement regarding estimates or accounting policies may result in changes to Arena’s guidance or previously reported results; the timing and outcome of regulatory review is uncertain, and lorcaserin may not be approved for marketing in combination with another drug, for another indication or using a different formulation or in any other territory for any indication; regulatory decisions in one territory may impact other regulatory decisions and Arena’s business prospects; government and commercial reimbursement and pricing decisions; risks related to relying on collaborative arrangements; the timing and receipt of payments and fees, if any, from collaborators; the entry into or modification or termination of collaborative arrangements; unexpected or unfavorable new data; nonclinical and clinical data is voluminous and detailed, and regulatory agencies may interpret or weigh the importance of data differently and reach different conclusions than Arena or others, request additional information, have additional recommendations or change their guidance or requirements before or after approval; data and other information related to any of Arena’s research and development may not meet regulatory requirements or otherwise be sufficient for (or Arena or a collaborator may not pursue) further research and development, regulatory review or approval or continued marketing; Arena’s and third parties’ intellectual property rights; the timing, success and cost of Arena’s research and development and related strategy and decisions; results of clinical trials and other studies are subject to different interpretations and may not be predictive of future results; clinical trials and other studies may not proceed at the time or in the manner expected or at all; having adequate funds; and satisfactory resolution of litigation or other disagreements with others. Additional factors that could cause actual results to differ materially from those stated or implied by Arena’s forward-looking statements are disclosed in Arena’s filings with the Securities and Exchange Commission. These forward-looking statements represent Arena’s judgment as of the time of this release. Arena disclaims any intent or obligation to update these forward-looking statements, other than as may be required under applicable law.

Contact: Arena Pharmaceuticals, Inc.

Craig M. Audet, Ph.D., Senior Vice President,
Operations & Head of Global Regulatory Affairs
caudet@arenapharm.com
858.453.7200, ext. 1612
www.arenapharm.com