Arena Pharmaceuticals, Inc.
Jan 25, 2008

Arena Pharmaceuticals Announces Initiation of Phase 1 Clinical Trial of Second Generation Niacin Receptor Agonist Under Its Collaboration With Merck & Co., Inc.

SAN DIEGO, Jan. 25 /PRNewswire-FirstCall/ -- Arena Pharmaceuticals, Inc. (Nasdaq: ARNA) announced today that Merck & Co., Inc. initiated a Phase 1 clinical trial of a second generation oral niacin receptor agonist under a collaboration between the companies to discover drugs for the treatment of atherosclerosis and other disorders. The initiation of this trial does not trigger a milestone payment.

"We are very pleased with the progress of this collaboration investigating the therapeutic potential of niacin receptor agonists to treat atherosclerosis and other disorders. We are looking forward to the Phase 1 results and the continued progress of the program," said Jack Lief, Arena's President and Chief Executive Officer.

Arena also announced that preclinical investigation of MK-0354, a first generation niacin receptor agonist being evaluated for indications other than atherosclerosis, was discontinued for compound specific reasons.

About Atherosclerosis

Atherosclerosis is characterized by the collection of fatty material deposits, such as cholesterol, along artery walls. This fatty material thickens, hardens, and may eventually block the arteries, adversely affecting blood flow and increasing the risk of heart attack and stroke over time. The American Heart Association estimates that atherosclerosis accounts for nearly 75% of all deaths from cardiovascular disease. HDL cholesterol, commonly known as the "good" cholesterol, can help clear the fatty deposits from the walls of blood vessels and transport cholesterol to the liver for processing and removal from the body. Drugs that can influence the levels of HDL cholesterol, or "good" cholesterol, may potentially provide clinical benefits to patients by reducing the risk of heart attack and stroke. The niacin receptor, a G protein-coupled receptor, or GPCR, is believed to have potential in regulating plasma lipid profiles, including HDL.

About Arena Pharmaceuticals

Arena is a clinical-stage biopharmaceutical company focused on discovering, developing and commercializing oral drugs in four major therapeutic areas: cardiovascular, central nervous system, inflammatory and metabolic diseases. Arena's most advanced drug candidate, lorcaserin, is being investigated in a Phase 3 clinical trial program for the treatment of obesity. Arena's broad pipeline of novel compounds targeting G protein-coupled receptors, an important class of validated drug targets, includes compounds being evaluated independently and with its partners, Merck & Co., Inc. and Ortho-McNeil Pharmaceutical, Inc.

Arena Pharmaceuticals® and Arena® are registered service marks of the company. "APD" is an abbreviation for Arena Pharmaceuticals Development.

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 the therapeutic and other potential of niacin receptor agonists; the results of the Phase 1 clinical trial of a second generation niacin receptor agonist; the continuation and progress of the collaboration between Merck and Arena and the activities and program thereunder; the niacin receptor's potential in regulating plasma lipid profiles; the potential of drugs that influence HDL cholesterol to provide clinical benefits to patients; and about Arena's strategy, internal and partnered programs, and ability to 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, planned clinical trials and studies may not proceed at the time or in the manner Arena expects or at all, the results of preclinical studies or clinical trials may not be predictive of future results, Arena's ability to partner lorcaserin, APD125, APD791 or other of its compounds or programs, the timing, success and cost of Arena's research, out-licensing endeavors and clinical trials, Arena's ability to obtain additional financing, Arena's ability to obtain and defend its patents, and the timing and receipt of payments and fees, if any, from Arena's collaborators. 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.

SOURCE Arena Pharmaceuticals, Inc.

CONTACT: Jack Lief, President and CEO, or David Walsey, Director,
Corporate Communications, both of Arena Pharmaceuticals, Inc.,
+1-858-453-7200, ext. 1682; or Mary Claire Duch, Media Relations of WeissComm
Partners, +1-212-301-7228, for Arena Pharmaceuticals, Inc.