The widely used diabetes drug Avandia got a new warning label Wednesday telling patients that it may, or may not, increase the risk of heart attacks.

Why the confusion? The Food and Drug Administration said studies of the risk are too contradictory to tell if Avandia really is riskier than other medications for Type 2 diabetes.

Still, the FDA put the controversy in a black box on the drug's label — the most severe warning the agency can require — at the behest of its scientific advisers, while it awaits further research to settle the issue.

Further complicating the new warning label: Patients may need a medical dictionary to interpret it. The warning says that Avandia may be associated with "myocardial ischemic events such as angina or myocardial infarction." In layman's terms, that's chest pain or a heart attack.

Type 2 diabetics who also have heart disease or are at high risk for it should talk with their doctor about Avandia's potential risk as they decide among treatment options, the FDA advised.

Avandia manufacturer GlaxoSmithKline PLC has agreed to begin a major new study comparing that drug to another active blood sugar-lowering medication to better understand if there is a risk.

About 1 million Americans with Type 2 diabetes use Avandia. It helps control blood sugar by increasing the body's sensitivity to insulin.