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: Orexigen Therapeutics (Nasdaq: OREX) popped as much as 11.6% in intraday trading today on relatively heavy volume.

So what: There's no real news about Orexigen today that could move the stock, nor on obesity drug competitors Arena Pharmaceuticals (Nasdaq: ARNA) and VIVUS (Nasdaq: VVUS). On the other hand, short interest in Orexigen has been high recently, and the stock is roaring back from a deep summer trough -- this could be a classic short squeeze.

Now what: If today's move is nothing more than pessimistic investors covering their shorts, this stock should fall back a few percent over the next day or two as the move runs out of steam. The Food and Drug Administration is evaluating several weight-loss drugs from Orexigen and its numerous competitors, and there are no guarantees that Orexigen will come out on top. You may be better off waiting for the FDA's final say before betting on any of these microcap hopefuls.

Fool contributor Anders Bylund holds no position in any of the companies discussed here. True to its name, The Motley Fool is made up of a motley assortment of writers and analysts, each with a unique perspective; sometimes we agree, sometimes we disagree, but we all believe in the power of learning from each other through our Foolish community. The Motley Fool is investors writing for investors.