At one point yesterday, Arena Pharmaceuticals (Nasdaq: ARNA) was up a maddening 22%. Shares ended the day up 6.5%. Even that's too much.

The reason for the buying spree? A press release about the company presenting data on its obesity drug, lorcaserin, at the European Congress on Obesity. The data presented at the medial meeting looks good; at two daily doses of lorcaserin, 46.3% (and 40.6% of single daily dosed) patients lost at least 5% of their body weight compared with 22.1% of patients on placebo. The Food and Drug Administration generally wants to see the drug group above 35% and double the control group.

But this wasn't new data. Arena combined the three phase 3 trials it ran for lorcaserin -- BLOOM, BLOSSOM, and BLOOM-DM -- to come up with the data. This type of meta-analysis might be interesting for researchers, but it isn't likely going to change the FDA's view of the drug. In fact, the inclusion criteria and analysis (Modified Intent-to-Treat with Last Observation Carried Forward analysis) for the meta-analysis sounds like something that would send shivers up the spine of FDA reviewers.

Arena still has an obese to-do list from the FDA before it'll sign off on the drug. And investors should keep in mind that there's no guarantee that Arena can satisfy the agency. I foresee the FDA being sticklers about every single item; the agency hasn't exactly been kind to the other obesity drug developers: VIVUS (Nasdaq: VVUS), Orexigen (Nasdaq: OREX) and Abbott Labs (NYSE: ABT).

Arena has four other drugs in its pipeline. They're all in phase 1 development, but at this point, investors would likely be better off watching those than reacting to meta-analysis data for lorcaserin.

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