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 VIVUS (NASDAQ:VVUS) have soared Monday by as much as 12% after the company scored a distribution deal with Express Scripts (NASDAQ:ESRX).

So what: Express Scripts has joined the Qsymia Certified Home Delivery Pharmacy Network, broadening VIVUS' distribution for its weight-loss pill that was launched just last month. Qsymia will be available through mail order. With Express Scripts being the country's largest pharmacy benefit manager, this deal is a boon for VIVUS.

Now what: Qsymia is the first to enter the obesity drug market in 13 years, and investors are clearly excited about its potential to boost the top line. The deal today is a good sign that VIVUS has a leg up on Arena Pharmaceuticals (NASDAQ:ARNA) and its competing Belviq drug for the time being. Belviq has already been cleared by the Food and Drug Administration, but hasn't been released into the market pending DEA clearance. For now, VIVUS has a first-mover advantage.

Fool contributor Evan Niu, CFA has no positions in the stocks mentioned above. The Motley Fool owns shares of Express Scripts. Motley Fool newsletter services recommend Express Scripts. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.