Look at almost any article about the potential for approval of VIVUS' (Nasdaq: VVUS) Qnexa this week, and you'll find a few Arena Pharmaceuticals (Nasdaq: ARNA) supporters bashing Qnexa. See my article from a few days ago for examples.

I think their animosity might be a little misguided.

Arena's marketing partner Eisai will soon launch Belviq into a wide-open obesity market. Roche sells Xenical, but it's not much of a competition. Abbott Labs (NYSE: ABT) pulled its obesity drug Meridia off the shelves in 2010. The approval of Qnexa would add legitimate competition.

But that's not necessarily a bad thing. Sure, any patient taking Qnexa is one fewer patient who could be prescribed Belviq, but many patients prescribed Qnexa won't respond to the drug, giving Belviq a chance to pick up the leftovers.

More important, though, the launch of two drugs has the potential to increase the overall obesity market faster than one sales team could do. It's very likely that doctors will prescribe both drugs to different types of patients. Keeping obesity drugs on doctors' minds and pointing out their availability to patients will increase prescriptions of both drugs no matter which drug the promotional material is for.

We don't know what Qnexa's label will look like, but it's almost guaranteed that the FDA will recommend doctors not give it to patients who are pregnant or might become pregnant; Qnexa contains the same active ingredient as Johnson & Johnson's (NYSE: JNJ) Topamax that's been shown to cause birth defects in babies born to mothers who took it.

Direct-to-consumer advertisements by VIVUS that drive patients intending to become pregnant to ask their doctors about Qnexa could result in the doctor prescribing Belviq instead of just sending the patient home empty-handed.

Only time will tell if the added free advertisement from VIVUS makes up for the added competition, but I don't see Qnexa's approval as the biggest obstacle for a successful launch of Belviq.

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