A two-day hearing at the Food and Drug Administration is expected to get underway later today on the controversial diabetes drug Avandia.

At its high water-mark, the one-time blockbuster pill generated $3 billion in sales for GlaxoSmithKline. In recent years, safety concerns prompted regulators to pull the drug in Europe, and it’s currently prescribed to only a tiny fraction of patients in the U.S.

Philadelphia College of Pharmacy Professor Jennifer Reinhold says problems first cropped up in 2007, after a New England Journal of Medicine article found the diabetes medication had a serious side effect.

“When they looked back at that data they found that potentially that cardiovascular risk was higher than what was originally reported,” she says.

In fact, it was a 43 percent increase in heart-attack risk for Avandia patients.

In 2010, the FDA restricted the use of the drug and sales plummeted in the United States. Since then, independent researchers at Duke have concluded Avandia doesn’t increase the risk of cardiovascular death.

Bloomberg Industries Senior Pharmaceutical Analyst Sam Fazeli says that doesn’t necessarily mean the drug is safe.

“This is the conclusion that some very significant key opinion leaders have reached after independently analyzing that data,” he says.

Critics continue to question Avandia’s safety.

Even if the FDA reverses course, Fazeli says drug maker GlaxoSmithKline may not re-enter what has become a very competitive diabetes market. But he says a positive recommendation could protect the company for liability.