Taking cough medicine does little to help recovery, US experts have said.
Giving children cough medicines could be harmful, US experts say
The American College of Chest Physicians has published guidelines for its members saying there was "no clinical evidence" they worked.
They suggest adults should use older non-prescription antihistamines and decongestants to stop the flow of mucus that causes the cough.
Children can be harmed by cough medicines, they warn, and they will usually get better without help.
It is possible children could be over-sedated with the medication, they said.
The guidance covers all aspects of treating cough. There is no equivalent guidance in the UK, but the British Thoracic Society is developing recommendations, due out at the end of this year.
Get better 'without help'
Dr Richard Irwin of the University of Massachusetts Medical School, who chaired the guidelines panel, said: "Cough is the number one reason why patients seek medical attention."
But he added: "There is no clinical evidence that over-the-counter cough expectorants or suppressants actually relieve cough."
Dr Irwin advised: "There is considerable evidence that older type antihistamines help to reduce cough, so, unless there are contraindications to using these medicines, why not take something that has been proven to work?"
He said coughs in children were worrisome and annoying, but added cough syrup was not the answer.
"Cough is very common in children. However, cough and cold medicines are not useful in children and can actually be harmful.
"In most cases, a cough that is unrelated to chronic lung conditions, environmental influences, or other specific factors, will resolve on its own."
Several studies have suggested that over-the-counter cough medicine do little more than offer comfort to patients.
Research published in the journal Pediatrics in 2004 suggested dextromethorphan, often listed on labels as DM, or diphenhydramine, an antihistamine, did not offer any more relief to children suffering from cough than sugar water.
But Francis Sullivan, a spokesman for Wyeth Consumer Healthcare, which makes the cough treatment Robitussin, said he did not expect the US guidelines to affect sales.
He said: "The US Food and Drug Administration has concluded that these drugs are safe and they work."
GP visits cut
Dr Richard Russell, of the British Thoracic Society, said: "The number of people with undiagnosed chronic cough is rising in this country and we need more effective treatments to help treat this condition, which can be really distressing.
"Over-the-counter (OTC) sales for acute cough medicines currently reach approximately £100m a year in the UK - money that is being spent on remedies, where evidence regarding their effectiveness is inconclusive."
He added: "More research is needed into new cough treatments, particularly for persistent cough."
But a spokesman for the Proprietary Association of Great Britain, which represents the makers of over-the-counter medicines, said the use of cough medicines meant people did not visit the doctor unecessarily.
It added: "Research carried out for PAGB in 2005 showed that in 86% of cases people used OTC cough mixtures to treat their coughs, whilst 8% sought advice from a doctor or pharmacist."