Shares of Arena Pharmaceuticals (NASDAQ:ARNA) have been on a roller coaster over the past 24 hours. It rose by 38% after hours on word that the company would release data for its obesity drug, lorcaserin, today. Then it opened down 10% after the data was released only to rebound and climb by 20% after management had its say.

That's the craziness of biotech for you.

I'm really not sure what management said that got investors so excited; the data is lackluster at best. Lorcaserin might be strong enough to get approved, but it still pales in comparison to efficacy data released by VIVUS (NASDAQ:VVUS) and Orexigen Therapeutics (NASDAQ:OREX).

For instance, VIVUS' Qnexa resulted in weight loss of 11.0% and 10.4%, beating placebo by about 9 percentage points in two recently completed trials. Lorcaserin, on the other hand, resulted in a 5.9% reduction in body weight, a mere 3 or 4 percentage points better than placebo, depending on which patient group you look at. Comparing data across trials can be deceptive at best, but in this case I think we can call a qualitative winner.

Sure, the drug is safe. It doesn't seem to have the heart problems that plagued Wyeth's (NYSE:WYE) fen-phen or the psychiatric problems that plagued drugs from sanofi-aventis (NYSE:SNY), Pfizer (NYSE:PFE), and Merck (NYSE:MRK). And management wants to argue that it'll be a first-line treatment for that reason alone.

But I have a hard time seeing doctors rushing to get their patients on lorcaserin when there may be other drugs on the market by then that help people shed so many more pounds. If doctors are looking for a low-risk solution, they might be better off prescribing diet and exercise changes than trying to eke out an additional 6- to 8-pound loss for a 200-pound person on lorcaserin.

There may be some smaller role for lorcaserin on the obesity market, just as there has been for other less-than-stellar diet drugs before it, but if you're looking for a blockbuster homerun, I'm not sure you'll find it in this Arena.

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Fool contributor Brian Orelli, Ph.D., doesn't own shares of any company mentioned in this article. Pfizer is a recommendation of the Inside Value newsletter service. The Fool has a disclosure policy.