Researchers who studied a variety of over-the-counter cough medicines found no evidence that they provide any significant relief. The study, conduced by researchers at the University of Bristol in England, appeared in the British Medical Journal.

Reviewed were 15 drug trials involving more than 2,000 patients that compared oral over-the-counter cough medicines with placebo in adults with acute cough. In nine trials, active treatment was no better than placebo. The positive results in the other six studies were of questionable clinical relevance, said the authors.

Based on their study, the researchers concluded, "Over the counter cough medicines for acute cough cannot be recommended because there is no good evidence for their effectiveness. Even when trials had significant results, the effect sizes were small and of doubtful clinical relevance."

"Although these medicines are generally well tolerated, their purchase could lead to unnecessary expense for the healthcare consumer," the study noted.