Over-the-counter cough syrups generally contain drugs in too low a dose to be effective, or contain combinations of drugs that have never been proven to treat coughs, said Dr. Richard Irwin, chairman of a cough guidelines committee for the American College of Chest Physicians.
Drugstore shelves are crowded with cough syrups promising speedy, often non-drowsy relief without a prescription.
But "the best studies that we have to date would suggest there's not a lot of justification for using these medications because they haven't been shown to work," said Irwin, a professor of medicine at the University of Massachusetts Medical School in Worcester, Mass.
The group's new cough treatment guidelines discourage use of over-the-counter cough medicines. Irwin said that not only are such medicines ineffective at treating coughs due to colds — the most common cause of coughs — they can also can lead patients to delay seeking treatment for more serious coughs, including whooping cough.
The guidelines strongly recommend that adults receive a new adult vaccine for whooping cough, approved last year.
The Consumer Healthcare Products Association, a trade group for makers of over-the-counter medications, disputed the guidelines and said over-the-counter cough medicines provide relief to millions of people each year.
The guidelines were published in the January issue of Chest, the American College of Chest Physicians' journal, released Monday. The recommendations have been endorsed by the college, the American Thoracic Society and the Canadian Thoracic Society.
Many popular over-the-counter cough medicines proudly advertise that they don't cause drowsiness, but Irwin said that is because they do not contain older antihistamine drugs that do help relieve coughs that are due to colds.
These antihistamines, including diphenhydramine — an active ingredient in Benadryl — are also available over the counter but are not marketed as cough medicines, he said.
Some over-the-counter cough syrups contain two drugs that have been shown to help relieve coughs caused by colds — codeine and dextromethorphan — but generally the doses are too small to be effective, Irwin said.
Dextromethorphan is in Robitussin, a top-selling over-the-counter cough syrup. It is among Robitussin ingredients that the Food and Drug Administration has found to be safe and effective, said Francis Sullivan, a spokesman for Wyeth Consumer Healthcare, which makes Robitussin.
Sullivan said Robitussin "wouldn't be a top brand if people didn't feel it was efficacious."
Coughs can have numerous underlying causes, including asthma, allergies, severe heartburn, postnasal drip and bronchitis.
Dr. Edward Schulman, an American Thoracic Society representative on the guidelines panel, said patients should see their doctors for coughs that linger longer than three weeks or are accompanied by shortness of breath, which could indicate pneumonia or other serious conditions.
Coughs due to colds usually last less than three weeks. Drinking lots of fluids can help relieve these coughs, and so can chicken soup, Schulman said.