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 biopharma company Vivus (Nasdaq: VVUS) were feeling ill today, slipping as much as 13% on higher-than-average volume.

So what: As if the obesity-drug developers needed any more bad news. Vivus, along with competitors Arena Pharmaceuticals (Nasdaq: ARNA) and Orexigen (Nasdaq: OREX), have been struggling to get the Food and Drug Administration to give a green light for one of their obesity treatments. The latest setback came today when the FDA said it plans to strengthen its safety warning on Topamax. Topamax is an epilepsy and migraine treatment from drug giant Johnson & Johnson (NYSE: JNJ), and the FDA is concerned about birth defects from a primary ingredient in the drug, topiramate. What does this have to do with Vivus? Its obesity drug, Qnexa, is a formulation of appetite suppressant phentermine and -- you guessed it -- topiramate.

Now what: Safety concerns seem to have set a particularly high hurdle for the obesity drug developers and, as such, this is bad news for Qnexa and Vivus. Of course while the fact that the FDA has cranked up its threat level on topiramate, it's not as if this were an unknown issue. The issues with topiramate were largely known, and the FDA had already highlighted the birth-defect issue with regards to topiramate and Qnexa.

On the flip side, while Arena and Orexigen have issues of their own to deal with, a setback for Vivus could mean be a positive for them if they can get their drugs to market (though that's a big "if" right now).

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