There's been plenty of research lately saying many non-prescription cough medicines don't help children with colds and might even cause harm. Now there's a study suggesting they don't help adults much, either.

"I do not give my kids over-the-counter cough medicine," said Thomas Fahey, professor of general practice at the Royal College of Surgeons in Ireland Medical School and review co-author. "I do not advise my patients to do so."

In their review, Fahey and colleagues looked at both children- and adult-focused studies. Some reported that OTC cough medicines helped patients; others said they did not. With conflicting evidence, the various studies presented a non-cohesive picture.

Conflicts of interest?

Another issue concerned the researchers, who wrote, "Six out of the nine studies that were supported by the pharmaceutical industry showed positive results compared to three positive studies out of 16 trials that did not report any conflict of interest."

On the other hand, "Most preparations appear to be safe based on those studies reporting side effects, which only described a low incidence of mainly minor adverse effects," the researchers found.

The review of the studies appears in the latest issue of The Cochrane Library, a publication of The Cochrane Collaboration, an international organization that evaluates medical research. Systematic reviews like this one draw evidence-based conclusions about medical practice after considering both the content and quality of existing medical trials on a topic.

The Cochrane review encompassed 25 studies, 17 of which involved 2,876 adults and eight of which involved 616 children.

During the past decade, physicians have increasingly voiced concerns about these medicines and the potential for overdosing young children.

In August, the U.S. Food and Drug Administration warned parents not to give over-the-counter cough and cold remedies to children under 2 years old without a doctor's approval. During a hearing before an FDA panel in October, federal health advisers said that children younger than six years should not take the medicines.

Cure worse than the disease?

Is it even necessary to cure a cough?

People often worry about a cough if it has not gone away after a week, Fahey said. Actually, the duration of a cough is commonly two weeks in children and three weeks in adults.

"I think there's the laymen's perception," Fahey said. The common conclusion is that "something should be done about it. It [coughing] is troublesome at night. But it is not a bad thing to be coughing. It could be helpful. It is a mechanism for shedding viruses."