NEW YORK - Arena Pharmaceuticals said its experimental obesity drug helped patients shed only about 10 pounds more than those taking placebos, sending its shares down 27 percent.

The company said it aimed to seek U.S. approval this year for Lorcaserin, a new type of obesity drug, based on the long-awaited new data that it said was favorable by a statistically significant margin.

Although the results technically satisfy the FDA requirements for approvability, we consider the weight loss benefits to be underwhelming at best, JPMorgan said in a research note.

The tiny San Diego company said the average patient taking Lorcaserin for a year had lost 8.2 percent of body weight, or 17.9 pounds. That compared with 3.4 percent of body weight, or 7.3 pounds, among patients taking placebos in the first of the company's three planned late-stage studies.

Lorcaserin met all its safety and efficacy goals, with an incidence of serious adverse events similar to placebo, Arena said.

Importantly, the 3,182-patient U.S. study showed no signs that the drug over a two-year treatment period caused heart valve damage, the problem that forced Wyeth (WYE.N) to recall its blockbuster fen-phen diet drugs in 1997. The recall cost Wyeth more than $21 billion in damages and legal expenses and has long cast a shadow over obesity treatments.

Like drugs used in fen-phen, Lorcaserin affects a messenger chemical called serotonin, but is designed to selectively target only one variety of the chemical -- and thereby sidestep heart-related side effects seen with Wyeth's withdrawn pills.

Arena said it expected to have final data from a second Phase III study in hand by September and hoped to ask U.S. regulators to approve Lorcaserin by year-end.

The future of Arena, which lost almost $240 million last year on revenue of less than $10 million, is highly dependent on whether the FDA approves Lorcaserin and whether patients embrace the treatment.

Shares of Arena fell to $3.30 in premarket trade from their closing price of $4.50 on Friday. (Reporting by Ransdell Pierson; Editing by Lisa Von Ahn)