Use of nonprescription medications for cough is common. In Great Britain, nearly $140 million is spent annually on these remedies, increasing by about 3 percent per year. Because patients frequently ask their physicians about nonprescription cough medications, Schroeder and Fahey reviewed the evidence for their effectiveness.

The authors used the Cochrane database, electronic literature searches, information from pharmaceutical companies and study authors, plus hand searching of journals and references to identify original, randomized, controlled clinical trials of nonprescription cough medications. Criteria for inclusion were acute cough of presumed viral origin with no indication of lower respiratory involvement or underlying respiratory illness, valid outcome measures of cough duration or frequency, cough of less than three weeks' duration, and use of a randomized control group that received placebo or no intervention.

From the 328 citations identified, 15 trials involving 2,166 patients met the criteria for analysis. The largest number of trials of a single medication was five. The trials were of generally poor methodologic quality, and the results could not be pooled because of the multiple differences among the trials.

In the five trials of antitussives, codeine was found to be equivalent to placebo in two studies. One study of dextromethorphan reported a significant reduction in cough frequency, while another trial found no difference compared with placebo. The single trial of moguisteine (not available in the United States) showed a significant reduction in cough scores for two to three days after treatment began, but this effect was not sustained, and 22 percent of patients reported gastrointestinal side effects.

One trial of the expectorant guaifenesin reported a significant benefit over placebo, but a second trial found no differences between the treated and placebo groups. Similarly, one trial of antihistamine-decongestant combinations reported significant benefit at three to five days, whereas a second trial found no improvement over placebo. Two trials of the antihistamine terfenadine showed that it was no more effective than placebo, but there was a low incidence of side effects. The single trial of mucolytics reported a significant reduction in cough frequency but offered no information on side effects.

The authors conclude that the evidence for use of nonprescription cough medications is limited. In nine of 15 trials, these medications were no better than placebo, and many were associated with side effects. When positive results were obtained, the clinical benefit was small and of questionable significance. The authors call for further studies in this area, stressing the importance of quality in study design and conduct. In the meantime, they do not recommend the use of nonprescription medications for treatment of acute cough of presumed viral origin.