GAITHERSBURG, Md., Dec. 8 — A panel of experts recommended Friday that doctors and patients be given stronger warnings about the dangers associated with the use of drug-coated stents in high-risk patients.

The panelists also recommended that the Food and Drug Administration warn doctors that if possible, such patients should remain on aspirin and Plavix, an anticlotting drug, for at least a year after a drug-coated stent implant.

The label on the Cypher stent, from Johnson & Johnson, approved for sale in the United States in 2003, calls for the anticlotting therapy for just three months. The label on the Taxus stent, from Boston Scientific, approved the next year, calls for six months on the drug.

At the end of the two-day hearing here, the panelists struggled to reach a consensus on most of the questions posed to it by the F.D.A. about whether it should restrict the use of the tiny devices, which are implanted to prop open heart arteries.

As the session ended, Daniel Schultz, head of the drug agency’s Center for Devices and Radiological Health, said it was too soon to discuss what specific actions the F.D.A. might take. “What I heard loud and clear is that we need to do a better job communicating to doctors and patients the best and latest information,” Dr. Schultz said.

The challenge the agency faces is that most of the stents — over 60 percent by the F.D.A.’s estimates — are being implanted in patients with more complex cardiovascular problems than those of the patients the devices were tested on.

The experts told F.D.A. officials that there was little reliable research comparing the risks associated with such “off label” use to the outcomes with drug treatment or surgery. And what research there is suggests that the risks of clotting, heart attack and death are higher for such high-risk patients than for those who were in clinical trial groups.

The stent market grew so explosively after the drug-coated devices were introduced in 2003 that regulators and consumers were caught with too little data. About one million Americans annually get stents — often more than one. Stents are implanted after tiny balloons have been inflated in clogged arteries to reopen blood flow, a procedure known as angioplasty.

The first stents were bare metal devices. The drug-coated products sharply reduced the frequency with which new blockages formed at the implant site, thus reducing the number of follow-up procedures. In the last year, though, it was discovered that the formation of potentially deadly clots long after implantation was slightly more common with the drug-coated stents than with bare-metal stents.

Doctors today commonly give the drug-coated stents without F.D.A. clearance to diabetics, people with weakened hearts or kidneys, and those with plaque blockages in three or more coronary arteries who hope the stenting will allow them to avoid bypass surgery.

Three medical societies, including the American Heart Association, have recommended that patients stay on anticlotting drugs for a year.

How the F.D.A. may address the issue is unclear. It cannot require the companies to recommend a drug program on their labels for an unapproved use of the device. And Bristol-Myers, which makes Plavix, is not allowed to market the drug for off-label stent use.

Many doctors are already recommending extended or even indefinite use of anticlotting drugs for stent patients. But the panelists pointed out Friday that no one knows the optimal length of time to take the drugs.

The anticlotting drugs can lead to excessive bleeding when a patient is in an accident and must be stopped if surgery or dental work is needed. Doctors also worry about whether patients will remember to take them every day and whether poorer patients can afford Plavix, which costs $1,400 annually for a daily dose.

“I haven’t heard anything today that’s going to change my practice when I go back to it Monday,” said Dr. Christopher J. White, a cardiologist on the panel from the Ochsner Medical Center in New Orleans. After a moment’s thought, though, he said he might cut back on the use of drug-coated stents where arteries branch since data showed clotting rates were higher where patients had overlapping stents.

Surgeons told the panel that a way to reduce risks was to cut back on the use of stents in most patients with blockages in three or more vessels or in the left main coronary artery — both cases in which data indicates survival rates are better for patients who undergo bypass surgery.