A panel of Food and Drug Administration advisers voted 8-8 on whether to allow continued marketing of the drug by drugmaker Abbott Laboratories. Earlier this year, European regulators banned the drug after the safety issues were raised.
Meridia has been sold since 1997, but data released in November showed patients with pre-existing heart disease were more likely to suffer traumatic heart attacks and strokes than patients taking a dummy pill. European regulators withdrew the drug in January based on the results, but the FDA wanted to seek the input of its advisers before making a decision.
Meridia is one of only three prescription drugs currently approved for weight loss.
The drug's benefits and risks present the FDA with a classic drug safety choice: whether to try to limit the use of the drug to patients who are likely to benefit, or recall it from the market and prevent any harm.
The agency is not required to follow the group's advice, and deputy director Dr. Eric Coleman offered little insight into how the FDA would interpret the panel's split vote.
"It certainly doesn't make things easier for us. You have to go back and dissect what people said and why they voted the way they did and then take it from there," Coleman told reporters after the meeting.
Nearly all of Wednesday's discussion centered on results from a 10,000-patient study released last year, which showed patients with heart disease taking Meridia had a more than 11 percent risk of cardiovascular risks compared with 10 percent of those taking a placebo.
The study was designed to show that weight loss with Meridia led to improved outcomes for patients with heart disease, diabetes or both.
Because the study failed to show those benefits, some panelists questioned the rationale for keeping it on the market, considering its modest weight loss benefits. On average, patients lost 5 pounds while taking the drug and about 30 percent of patients achieved lasting weight loss while on the drug.
"We do make the assumption that weight loss is beneficial and that it translates into clinical benefits, but we're not presented with those here," said Dr. Katherine Flegal, of the Centers for Disease Control and Prevention. "On the whole, there are not the benefits that justify the risks."
Flegal was one of eight panelists who voted to remove the drug from the market. Six voted to leave the drug on the market but add a boxed warning label and limit prescribing to select doctors. Two other panelists said the drug could be left on the market with only a labeling change.
Panelists who favored continued marketing of the drug said there are health benefits from weight loss that didn't show up in the study of heart outcomes.
"I think that just because we didn't measure the benefits scientifically doesn't mean they don't exist," said Dr. Jessica Henderson of Western Oregon University. "I don't think a consumer's right to have that treatment should be taken away just because the scientists didn't do their job."
Meridia is not widely used in the U.S., with a steep decline in prescriptions in recent years. About 283,000 prescriptions for it were filled last year, just more than half the number in 2005. The typical patient stays on the drug for only about 50 days, according to FDA figures. Eighty percent of users are middle-aged women.
Abbott said in a statement after the meeting that Meridia "is an important option for patients and physicians to treat a serious condition for which there are few treatment options currently available."
The company laid out a multi-pronged plan for managing Meridia's safety risks, including new warning labels and instructions for doctors to stop prescribing the drug if patients don't respond within two or three months.
But FDA staffers said this strategy wouldn't necessarily address Meridia's risks, because most patients use the drug for less than two months.
Weight loss drugs have long been plagued by negative side effects - particularly heart problems. In the same year Meridia was approved, Wyeth's diet drug combination, fen-phen, was pulled off the market because of links to heart-valve damage and lung problems.
The FDA is reviewing a new generation of diet pills. On Thursday, the same FDA panel will review a new weight loss pill from Arena Pharmaceuticals. Analysts have speculated that the drug, lorcaserin, would coast to an easy FDA approval because of its safety profile. But an FDA review released earlier this week highlighted potential safety issues including heart valve disease, depression and malignant tumors seen in animal studies.