The fact that people keep buying the medicines is itself evidence

EDITOR—Schroeder and Fahey are right to urge caution in interpreting the results of their systematic review on cough medicines, and their recommendation to change existing guidance on cough medicines in the United Kingdom is not justified.1

Their review considered a heterogeneous group of products that included many different active ingredients from several different drug classes. It is surely impossible to draw from this any meaningful conclusions about over the counter cough medicines as a whole. Many of the products and active ingredients in the reviewed trials are either not available at all in the United Kingdom (moguisteine, bromhexine), are only available on prescription (salbutamol, terfenadine), or are not indicated for the relief of cough (loratidine, terfenadine).

Only 15 trials were included in the review, and only one reported a power calculation. As the authors concede, it seems highly likely that many of the remainder did not include sufficient patients to detect a difference from placebo, should one exist. The predictable upshot of this is that the review showed no …