he cure for the common cold remains as elusive as ever. A federal advisory committee recommended yesterday that the first drug aimed at treating the cause of the cold rather than just its symptoms not be approved.

In a unanimous decision, the Food and Drug Administration's advisory panel on antiviral drugs said there were too many questions about the safety of the drug, which is made by ViroPharma (news/quote) of Exton, Pa., to allow its widespread use merely to shorten the duration of an ailment that is not life-threatening and goes away by itself.

"It's a mild, self-limited illness, and it's very common," Dr. Roy M. Gulick, associate professor at Weill Medical College of Cornell University and chairman of the panel, said in an interview. "Literally, millions of people could be taking the drug." For such a drug, he said, the safety aspects must "be very well known and clean."

The F.D.A. usually follows the recommendations of its advisory panels, which are made up of outside experts.

The decision is a blow to ViroPharma and to Aventis (news/quote), the European pharmaceutical giant that would market the drug in the United States and Canada. ViroPharma has no other drugs on the market or in advanced clinical trials.

Martin J. Driscoll, head of commercial operations at ViroPharma, said yesterday, "We remain optimistic that we can do the necessary work to address the concerns expressed by the committee today and ultimately gain approval for the product."

The drug, known as Picovir, has attracted attention because it directly attacks a family of viruses, known as picornaviruses, that cause half or more of the billion colds caught in the United States each year. The drug lodges in a pocket in the virus's coat, interfering with the germ's ability to infect cells and make copies of itself. Other cold remedies only suppress symptoms, like runny noses or coughs.

In clinical trials, Picovir shortened the length of the cold to roughly six days from seven. Patients took the pills three times a day for five days. But the first treatment has to start within 24 hours of the onset of symptoms, which some panel members said might be difficult with a drug sold by prescription.

While the F.D.A.'s own staff reviewers said the results of the clinical trials were "variable," the advisory panel members reached a consensus that the drug worked, Dr. Gulick said. The major concern, he said, was that Picovir appeared to lower the effectiveness of oral contraceptives. And some women taking both Picovir and birth control pills experienced bleeding between menstrual periods.

The panel also questioned whether the drug could be used by the general population because the participants in the clinical trial were mainly young, white, otherwise healthy women. "It was in women and nonsmokers that it had the best benefit," said Dr. Princy N. Kumar, chief of the division of infectious diseases at Georgetown University Medical Center and a panel member.

Another concern was that the virus seemed to mutate to develop resistance to the drug.

ViroPharma's stock did not trade yesterday because of the panel meeting. It closed on Monday at $13.41 after dropping 18 percent last week because of analysts' predictions that the drug would be rejected.

Aventis paid $25 million for the North American marketing rights for Picovir, but ViroPharma may have to refund as much as $20 million of that if certain milestones are not met. The details of those have not been disclosed.