Federal health officials asked experts Thursday whether the drug-coated stents used to prop open the arteries of about 3 million people in the U.S. pose a heightened risk of death or raise other safety concerns that require action.

The two manufacturers of the widely used devices say their benefits outweigh their risks, but the Food and Drug Administration believes patients could face a small but significant chance of blood clots.

The companies, Boston Scientific Corp. and Johnson & Johnson, were in the hot seat as the FDA began two days of meetings to discuss with a panel of outside experts the clotting risks associated with the devices.

Some researchers believe that clotting leads to an increased risk of heart attack and death in patients fitted with the devices — a danger the FDA said is unknown. The agency does believe the clotting risk is real, however.

"Are you certain of that conclusion?" asked panel member Dr. John Somberg, of Rush University Medical Center in Lake Bluff, Ill.

FDA medical officer Dr. Andrew Farb said yes, after acknowledging the difficulty of acting on that information.

"When we have rare events in relatively small numbers, to come up with sweeping conclusions can raise issues," Farb said.

The FDA asked panelists to assess the risk and then provide the agency with their recommendations, including whether to update the labels with new warnings or change guidelines on how long people should take anti-clotting drugs such as Plavix and aspirin following stent surgery.

"It is important to note FDA does not regulate the practice of medicine. However, FDA is responsible for any use of a device that raises a public health concern," FDA medical officer Dr. Takahiro Uchida told the panel.

Boston Scientific acknowledges a slight increase in clotting associated with its drug-coated stent, the Taxus. The company said it has seen no corresponding increase in heart attacks or deaths.

Johnson & Johnson said there is no significant difference in clotting, heart attack or death rates between its stent, the Cypher, and bare metal versions.

Both companies said use of the drug-coated stents reduces the need for follow-up surgeries to reopen clogged arteries when compared to bare-metal stents. That accounts for the widespread use of the drug-coated versions since their introduction in 2003. Today, more than 60 percent of the stents probably are implanted in higher-risk and other patients not studied before the devices gained FDA approval.

Multiple studies have suggested the risk of blood clots, heart attack and death rises in patients who stop taking Plavix earlier than now recommended. Some doctors recommend patients stay on it indefinitely until more is learned.

But FDA staff said it is unknown how long patients should take the drug, distributed by Bristol-Myers Squibb Co. and Sanofi-Aventis SA.

The FDA also seeks 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.