"I'm chalking it up to short covering in a market that is taking risk down," said a biotech hedge fund manager. "Real investor buying may be part of it but 20% of Arena's float is short." It's also not uncommon to see biotech stocks run up into FDA approval decisions as momentum investors try to play any short-term pop in price and volume. Arena certainly fits this category, perhaps even more so given the high-profile nature of weight-loss drugs in general. Whether or not FDA approves lorcaserin on June 27 or delays approval for a short time, Arena and its marketing partner Eisai are not expected to launch the drug commercially until early next year. The FDA is also reviewing Vivus' ( VVUS) weight-loss drug Qnexa, with an expected decision date of July 17. --Written by Adam Feuerstein in Boston. >To contact the writer of this article, click here: Adam Feuerstein. >To follow the writer on Twitter, go to http://twitter.com/adamfeuerstein. >To submit a news tip, send an email to: email@example.com. Follow TheStreet on Twitter and become a fan on Facebook.