GlaxoSmithKline’s (GSK) diabetes drug Avandia has such frightening side effects that the FDA will probably make it carry a "black box" label. Studies have found that the treatment can increase risk of heart attack.

Concerns about the side effect drove sales of the drug down 48% in the US during the September quarter.

Glaxo CEO Jean-Pierre Garnier told Reuters that sales might return if the "black box" warning is not too severe. "Absolutely. It all depends on what the language is," he said.

So, the FDA will have to tone down the part about heart attacks.

Douglas A. McIntyre