Diabetes drugs Avandia (rosiglitazone) and Actos (pioglitazone) -- members of a class of drugs called thiazolidinediones -- will soon carry a "black box" warning on the potentially heightened risk of congestive heart failure in some patients.

FDA Commissioner Dr. Andrew von Eschenbach, told Congress June 6th the agency had decided that the two diabetes drugs should carry the more prominent warning because "despite existing warnings, these drugs were being prescribed to patients with significant heart failure."

According to von Eschenbach's testimony, the request for the warning -- the strongest possible -- was issued to both companies May 23 following publication in the New England Journal of Medicine of a study that found Avandia increased the risk of heart attack by as much as 43 percent.

Following the release of the NEJM study on Avandia, the FDA issued a safety alert but said more analysis was needed before taking further action..

Meanwhile, the FDA announced an advisory panel will meet on July 30 to weigh the cardiovascular risks of the thiazolidinediones class of diabetes drugs.

In response to the growing controversy over Avandia's safety profile, the American Diabetes Association also issued an advisory statement.

"As a result of all of this information, the American Diabetes Association strongly encourages patients taking this medication to consult with their physician as to its benefits and risks," the organization said.

"The Association also reminds patients, however, that they should not stop taking any prescribed medications without first discussing the issue with their health-care provider."