Why not?

So they're finally found a drug that helps people lose weight. It apparently also helps prevent diabetes. Drug helps prevent type 2 diabetes
And at the end of the story, here's the killjoy: "Dr. Despres cautioned that rimonabant is not intended as a quick fix for those who want to pop a pill to shed a few pounds, saying it should be prescribed only for those at risk of diabetes and heart disease who have not responded to other means - such as diet and exercise - to improve their health. "It has to be said loud and clear, this won't be a weight-loss drug, it won't be a miracle drug. This is really, really the wrong approach."
Well, I am using a drug to quit smoking. So can someone please tell me why is using a drug to lose weight "the wrong approach"?
Party pooper!