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 anti-obesity drug maker VIVUS (NASDAQ:VVUS) shot higher by as much as 22% earlier in the trading session today following a decision by insurer Aetna (NYSE:AET) to begin providing coverage on Qsymia.

So what: In addition to Qsymia, Aetna also announced that it'd be covering Arena Pharmaceuticals' (NASDAQ:ARNA) Belviq when it finally makes it to pharmacy shelves. Thus far, VIVUS' Qsymia, which was seen as a potential blockbuster drug, has performed miserably, with roughly 30% of prescriptions left at pharmacies because patients have had to pay for the drug out of their own pockets, according to VIVUS' chief commercial officer, Mike Miller. Today's move should clear the way for some of those patients to begin to receive partial insurance coverage of Qsymia prescriptions and could cause other insurers to soon jump on board.

Now what: Before you get too excited, don't! Let's recall that every sales estimate out there has been blatantly inflated thus far, so it'd probably be wise to give Qsymia a quarter or two more before we make our final judgment as to whether or not it's being well accepted by physicians and patients. What we do know is that Arena's Belviq is in line to be the first internationally approved anti-obesity drug on the market, not VIVUS' Qsymia, and that Orexigen Therapeutics' (NASDAQ: OREX) Contrave is still years away from commercial production due to safety test delays and the need for further clinical trials. In short, Arena's currently in the driver's seat and everyone else is just along for the ride.

With a European approval now off the table for VIVUS, what's next for the fat-busting drug maker? Find out by getting your copy of our latest premium research report on VIVUS. Packed with in-depth analysis on the opportunities and threats facing VIVUS – and complete with a year of regular updates – this report will give you the tools needed to make smart long-term investing decisions. Click here to learn more.