A review of studies involving over-the-counter cough syrups found no good evidence for or against their effectiveness.
A total of 25 studies were analysed — 17 based on 2,876 adults and eight based on 616 children.
They covered antitussives, which are used to relieve coughs; expectorants, which promote the discharge of mucus from the respiratory tract; and combinations of drugs such as antihistamine and decongestant. The studies produced conflicting or variable results.
Some showed syrups worked no better than a placebo, which is a substitute designed to trick people into thinking they are taking the real thing.
Other mixtures had “satisfactory” responses compared with a placebo, researchers said.
The research was carried out with the help of Thomas Fahey, professor of general practice of Dublin’s Royal College of Surgeons in Ireland medical school.
Professor Fahey said: “I do not give my kids over-the-counter cough medicine. I do not advise my patients to do so.”
Prof Fahey said people often worry about a cough if it has not gone away after a week.
But the duration of a cough is commonly two weeks in children and three weeks in adults.
“I think there is the laymen’s perception,” he said, with the common conclusion being that “something should be done about it”.
This was especially true if coughs were troublesome at night.
“But it is not a bad thing to be coughing,” he added. “It could be helpful. It is a mechanism for shedding viruses.” He said patients would be as well to take pain-relief medication such as paracetamol or just breathe in steam.
The review of the studies appeared in the latest issue of the Cochrane Library, a publication of the Cochrane Collaboration, which evaluates medical research.
Two years ago US researchers said taking cough medicine did little to help recovery.
The American College of Chest Physicians published guidelines for its members saying there was “no clinical evidence” they worked.
The Proprietary Association of Great Britain, which represents manufacturers of over-the-counter medicines, said regulatory agencies worldwide supported the use of cough medicines.
It said studies supported the efficacy of their active ingredients.
Sheila Kelly, executive director of the group, said: “It is important for both adults and children, suffering from self-limiting cough during a cold or flu episode, to have access to a wide range of effective over-the-counter cough treatments.
“We believe they remain both safe and effective if used according to the instructions on the pack.”
She said products on the market have successfully demonstrated their efficacy through decades of use by consumers.
“However, if consumer have any concerns they should seek advice from their doctor or pharmacist,” she said.