Earlier, GlaxoSmithKline said its second-best-selling drug was no more dangerous to the heart than other diabetes pills. But a Food and Drug Administration drug safety scientist said Avandia was too risky and offered no advantage over alternatives.
"The compass needles for (Avandia) ... all point to an increase in coronary heart disease risk," Dr. David Graham told the panel of experts from outside the agency.
Dr. Gerald Dal Pan, head of the FDA office that reviews the safety of drugs after approval, said he agreed with Graham that Avandia's benefits did not outweigh the risks.
Millions of diabetics around the world take Avandia now. The drug's safety came into question in May when a Cleveland Clinic analysis linked the drug to a 43% higher chance of having a heart attack.
Other FDA officials said they remain unsure if the drug truly contributes to heart attacks, pointing to other research that conflicts with that finding.
"It's important that the committee understand there is a fundamental disagreement within the (Center for Drug Evaluation and Research) on the scientific conclusions that should be drawn," said Dr. Robert Meyer, director of the FDA office that reviews diabetes drugs.
The agency is asking the advisory panel if taking Avandia makes a heart attack more likely, and if so, how the dangers compare to other diabetes drugs.
If the advisers decide Avandia should stay on the market, the FDA will ask about other steps, such as adding a strong "black box" warning or limiting use to certain patients.
Panel deliberations are closely watched because the FDA usually follows the group's advice. Recommendations from the panel are expected later on Monday.
About 21 million Americans have type 2 diabetes, a disease in which the body does not adequately control blood sugar. Patients are at risk for heart disease, kidney failure, limb amputations and other serious complications.
Glaxo said Avandia should remain an option because many patients need multiple drugs to keep blood sugar under control, and a portion of them cannot take some of the other therapies.
"There is no overall evidence that (Avandia) is different from other oral anti-diabetic agents" with regard to heart attack risk, Murray Stewart, Glaxo vice president for clinical development, told the panel.
The FDA's Graham, however, said his analysis showed the drug did increase heart attacks and other cardiac problems while rival drug Actos, made by Japan's Takeda Pharmaceutical, did not.
The safety controversy has hurt Avandia sales. Worldwide sales in the three months to June dropped to 349 million pounds from 477 million a year ago, the company reported last week.
Avandia is known generically as rosiglitazone, while Actos is known as pioglitazone. Both drugs are so-called thiazolidinediones that were designed to make the body more sensitive to insulin, a hormone the body needs to convert sugar into energy.