By an 11-1 vote, the committee said available data was "supportive" of the effectiveness of phenylephrine at 10 milligrams, the dose sold over the counter. Members also called for new and larger studies of that dose, mainly because available data came from small studies.
"The evidence is not conclusive," Dr. Mary Tinetti, the panel's chairwoman, told reporters after the meeting.
The committee, in a 9-3 vote, also urged new research to see if a higher 25-milligram dose worked and was safe.
FDA reviewers said seven of 14 studies found a 10-milligram dose of phenylephrine improved resistance inside the nose, a measurement once used to assess congestion. Much of the research on phenylephrine was done in the 1960s and 1970s.
"Based on the science, which I think was solid but very narrow, we do have seven studies that show significant improvements," said panel member Ralph D'Agostino, a Boston University statistician.
Makers of phenylephrine products include J&J, Schering-Plough Corp and Merck & Co Inc.
The manufacturers said phenylephrine had been used safely and effectively by millions for 40 years. Consumers have taken more than 5 billion doses over the past decade, according to the Consumer Healthcare Products Association (CHPA), which represents over-the-counter drugmakers.
The industry will work with the FDA to "add to the body of evidence for 10 milligrams," CHPA President Linda Suydam said.
There are no convincing data that a 25-milligram dose is necessary, CHPA said in a statement.
Phenylephrine's use increased after a 2005 law required that pseudoephedrine products be kept behind the pharmacy counter, a move meant to prevent illegal conversion of pseudoephedrine into the stimulant methamphetamine.
A petition filed with the FDA in February by University of Florida researchers argued that 10 milligrams of phenylephrine had not been proven any better than a placebo at easing nasal congestion. Some research suggested 25 milligrams would work, the petition said.
"The data available do not support the conclusion that phenylephrine 10-milligrams is effective" as an oral decongestant, Randy Hatton, a pharmacist at the University of Florida and one of the petitioners, told the advisory panel.
Friday's FDA panel considered only adult use of phenylephrine. The FDA is considering a previous panel recommendation that a variety of over-the-counter cough and cold medicines should not be given to children under 6 because evidence of a benefit is lacking.
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