Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of drug developer Arena Pharmaceuticals (Nasdaq: ARNA) were putting on some weight today, gaining as much as 22% on heavy volume.

So what: This morning, Arena issued a press release revealing the data analysis that the company presented at the European Congress on Obesity. Specifically, the company showed that in its phase 3 clinical trial program, subjects taking its lorcaserin drug were more likely to lose weight than those on a placebo. The company also noted that adverse reactions were relatively mild.

Now what: While the data analysis is interesting, investors still have to face the nagging question of whether the Food and Drug Administration will actually approve the drug. Back in October, the FDA turned the drug down due to concerns over efficacy and cancer risk. Does today's news change that picture? The Associated Press quoted Lazard analyst William Tanner, who says it doesn't and that the prospects for approval still look dim.

Want to keep up to date on Arena Pharmaceutical? Add it to your watchlist.