Drug-coated stents that buttress the arteries are safe when used as directed, health advisers say, even though the risks they may pose to the majority of patients with the devices remains an open question.

Since the first of the drug-eluting stents was introduced in 2003, the devices have gone on to capture 80 percent of the stent market from the older, bare-metal versions. About 3 million Americans now have one or more of the newer stents in their bodies.

Food and Drug Administration approval of the devices covered only a narrow patient population. Today, doctors implant the stents in a far greater variety of patients, including people with narrower or more complicated arteries not originally seen as suitable for the devices.

That so-called "off-label" use now accounts for at least 60 percent of the drug-coated stents implanted, according to the FDA.

The stents combine a tiny mesh tube, used like scaffolding to prop open arteries, and a drug coating. The drugs elute, or dissolve, into the body to prevent reclogging of arteries that can require follow-up surgery. That's their advantage over the plain, bare-metal stents.

The FDA is concerned by what it calls a small but significant increased risk of clotting associated with the combination stents. An outside panel of experts convened by the agency is in the midst of examining the issue and recommending what steps the FDA take next.

The two-day meeting wraps up late Friday. On Thursday, the panel said the stents don't increase the risk of heart attack or death when used as labeled, but may put patients at risk for blood clots.

The FDA then asked the panel to examine Friday the off-label use and whether those patients face similar risks.

The two companies with U.S. approval to sell the stents, Boston Scientific Corp. and Johnson & Johnson, said there is no increased risk in those patients or, if there is, that it's likely attributable to the health status of the patients. With stents, off-label use typically involves more complex cases, often in patients suffering from poorer health.

On Friday, the FDA also will seek recommendations for research on the drug-coated stents on the market or pending approval. Both Medtronic Inc. and Abbott Laboratories hope to enter the more than $5 billion U.S. market for the drug-coated stents.