Researchers at the University of Bristol reviewed 15 trials, involving over 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, say the authors.
Because of the small number of trials, these results should be interpreted with caution, say the authors. However, the advice given by NHS Direct to use over the counter cough medicines should be restricted until more evidence becomes available on their effectiveness, they conclude.