The present study evaluatedthe effectiveness of diphenhydramine against cough due to respiratory infectionor irritation in patients without comorbidities. The researchers searchedMedline (1966-2005), Embase (1980-2005), Cochrane and references from retrievedarticles and included studies/clinical trials using keywords such asdiphenhydramine (OR dimenhydrinate), antitussive agents, cough. These studieswere then blinded to study origin selected studies, inclusion criteria wasdiphenhydramine monotherapy against placebo, double-blinded, randomized,clinical trial, intention-to-treat, dropout information. The blinded reviewers assessedthe selected studies on a quality scale.

Among the total reviewedstudies, 11articles were recognized, 7 were rejected, remaining 4 articles thatwere included in the analysis and scored 20, 21, 25 and 26 out of a maximum of32. A total of 162 people were observed, 65 on diphenhydramine, 63 on placeboand 34 in a crossover setting in these selected studies. The results from the crossoverstudies showed remarkable efficacy; 27-56% reduction in 20 healthy volunteersand 21-26% reduction in 13 patients.

However, the evidences arestill limited assessing the efficacy of diphenhydramine in the treatment ofcough, diphenhydramine in crossover studies has shown its therapeutic potentialin the treatment of cough.

Source: Björnsdóttir I,Einarson TR, Gudmundsson LS, Einarsdóttir RA. Efficacy of diphenhydramineagainst cough in humans: a review. Pharm World Sci. 2007 Dec;29(6):577-83.