Cough medications have been under scrutiny of late, with concerns that for children, they are ineffective and may actually cause harm. Now, a new review of the products finds that they may not help adults much either.

The review was conducted by the Cochrane Collaboration, an international organization that evaluates medical research.

The researchers originally looked at 328 potentially relevant studies but eliminated most of them for various reasons such as they weren't placebo controlled; or they used participants with chronic cough lasting more than three weeks of they didn't use a medication readily available over the counter.

They narrowed down the list to 25 studies involving 3,492 patients --17 of the studies were conducted in adults, eight in children.

In total, 10 of the 25 included trials showed a positive result, whereas the other 15 did not show that the medications were any better than a placebo.

Among the 17 studies conducted on adults:

• Six trials compared cough suppressants (antitussives) with placebo and had variable results.
• Two trials compared the expectorant, guaifenesin with placebo. One indicated significant benefit whereas the other did not.
• One trial found that a mucolytic reduced cough frequency and symptom scores.
• Two studies examined antihistamine-decongestant combinations and found conflicting results.
• Three studies compared other combinations of drugs with placebo and indicated some benefit in reducing cough symptoms.
• Three trials found antihistamines were no more effective than placebo in relieving cough symptoms.

The study authors say the results of their review have to be interpreted with caution because the number of studies in each category of medication was small.

As well, many of the studies were of poor quality and the methods used to test them varied. For example, five studies testing cough suppressants used short-term cough relief after a single dose as an outcome, while others used longer timelines. Outcomes were also assessed in different ways, including through patient questionnaires, acoustic signals, tape recordings, or assessment by a physician.

So after reviewing all the studies, the authors say they could find no good evidence for or against the effectiveness of over-the-counter medicines for coughs. But they say what is really needed are better studies.

"Higher quality evidence is needed to determine the effectiveness of self-care treatments for acute cough," they conclude.

At the same time, the reviewers also found little evidence that cough medications do any harm. "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 authors write.

The authors note that nine of the 25 studies were fully or partly supported by pharmaceutical companies which provided grants, supplied the drugs in question or gave assistance with the study. Six of the nine studies supported by the pharmaceutical industry showed positive results, compared to three out of 16 trials where no support was reported.

Gerry Harrington director of communications for the Nonprescription Drug Manufacturers Association of Canada says the conclusions of this review are "misleading and potentially irresponsible."

"They are unhelpful and confusing for consumers," he says, noting that many of the products included in the review are not approved for use in Canada.

"The science is pretty solid," he told CTV News. "There is nothing to suggest there is a problem with adult cough preparations sold in Canada."

Dr. Thomas Fahey of the Royal College of Surgeons in Ireland Medical School and one of the authors of the review, says he's not convinced that cough medications work at all.

"I don't take them and I don't recommend patients take them," he told CTV News in a telephone interview.

"There's a multi-billion dollar industry here and remarkably poor evidence about the benefits or even side effects."

Fahey believes that better studies need to be done on the ingredients in these products to settle once and for all whether they work.

"There is also a need to identify ineffective preparations in order to lower costs for consumers and health care providers," he and his co-authors add.

Dr. Michael Reider of the Children's Hospital of Western Ontario says he's not sure that it's necessary to take anything for a cough, since most coughs will last two to three weeks regardless of what medications are used.

"There's a chance these products may work for you but there's a greater chance they won't."

"If I were an adult with a viral cough, I'd tough it out. When I get a cough, I use Tylenol or Advil for the pain, lots of fluids and take it easy."

For the meantime, U.S and Canadian health officials advise that the cough medications along with cold medications should not be given to children under two, unless recommended by a doctor.

And the Food and Drug Administration in the U.S. is still discussing whether cough and cold products should be used at all in children aged two to 11. A decision on that matter is expected in the coming months.

With a report from CTV medical specialist Avis Favaro and producer Elizabeth St. Philip