WASHINGTON — The cold and cough medicines long used by parents to treat their children’s runny noses and other symptoms don’t work and shouldn’t be used in those younger than 6, federal health advisers recommended Friday.

The over-the-counter medicines should be studied further, even after decades in which children have gotten billions of doses a year, the outside experts told the Food and Drug Administration. The FDA isn’t required to follow the advice of its panels of outside experts, but does so most of the time.

“The data that we have now is they don’t seem to work,” said Sean Hennessy, a University of Pennsylvania epidemiologist, one of the FDA experts gathered to examine the medicines sold to treat common cold symptoms. The recommendation applies to medicines containing one or more of the following ingredients: decongestants, expectorants, antihistamines and antitussives.

The nonbinding recommendation is likely to lead to a shakeup in how the medicines — which have long escaped much scrutiny — are labeled, marketed and used. Just how and how quickly wasn’t immediately clear.

In two separate votes, the panelists said the medicines shouldn’t be used in children younger than 2 or in those younger than 6. A third vote, to recommend against use in children 6 to 11, failed.

Earlier, the panelists voted unanimously to recommend the medicines be studied in children to determine whether they work. That recommendation would require the FDA to undertake a rule-making process to reclassify the medicines, since the ingredients they include are now generally recognized as safe and effective, which doesn’t require testing. The process could take years, even before any studies themselves get under way.

Simply relabeling the medicines to state they shouldn’t be used in some age groups could be accomplished quicker, FDA officials said.

Indeed, the drug industry could further revise the labels on the medicines to caution against such use. The Thursday-Friday meeting came just a week after the industry pre-emptively moved to eliminate sales of the nonprescription drugs targeted at children younger than 2.

Pediatricians pushing for greater restrictions told the FDA advisers Thursday that the over-the-counter medicines shouldn’t be given to children younger than 6, an age group they called the most vulnerable to any potential ill effects.

But FDA officials and panelists agreed there’s no evidence they work in older children, either.

Still, panelists held off from recommending against use in older children. Some said they feared such a prohibition wouldn’t eliminate use of the medicines by parents.

“They will administer adult products to their children because they work for them or feel they work for them,” said the panel’s patient and family representative, Amy Celento of Nutley, N.J.

The drug industry says the medicines, used 3.8 billion times a year in treating cold and cough symptoms in children, do work and are safe. It says more parent education is needed to avoid overdoses that in rare cases have been fatal.

A group of pediatricians petitioned the FDA earlier this year seeking action on the medicines.

An American Academy of Pediatrics official earlier Friday told the experts that the medications should be relabeled to tell parents they don’t work in children younger than 6 and may be dangerous.

“Why not label these products with what we actually know?” asked David Bromberg, a Frederick, Md., pediatrician.

Some of the drugs — which include Wyeth’s Dimetapp and Robitussin, Johnson & Johnson’s Pediacare and Novartis AG’s Triaminic products — have never been tested in children, something flagged as long ago as 1972 by a previous FDA panel.

An FDA review found just 11 studies of children published over the last half-century. Those studies did not establish that the medicines worked in those cases, according to the agency.

For the most part, the results from tests in adults have been extrapolated to determine whether the medicines work in children. But even that evidence is “modest at best,” said panel chairwoman Dr. Mary Tinetti of Yale University School of Medicine. Indeed, all but one of the 22 panelists then voted to say that extrapolation is unacceptable.

The panel also recommended that drug makers provide standardized droppers with their liquid cough and cold medicines. Experts had told the panel the sometimes hard-to-use dosing devices contribute to parents unwittingly overdosing their children.

Later Friday, the panel recommended the dizzying array of medicines that combine multiple ingredients remain on the market — but only pending the results of future studies to determine if they work.

The panel also said cold and cough medicines should not be allowed to bear “doctor-recommended” and similar statements. It wasn’t immediately clear if such a prohibition would be constitutional.

One health expert told the panel that children catch five to eight colds a year. Those colds don’t necessarily require treatment beyond comfort measures that don’t involve drugs, said Patricia Jackson Allen, of the National Association of Pediatric Nurse Practitioners.