A study published on bmj.com today has found that reviews of drugs which are supported by the pharmaceutical industry are less transparent, and are more likely to reach favourable conclusion on drugs, than independent reviews.

According to the authors, bias in drug trials is common and often favours the trial-sponsor's product. To balance this effect, independent reviews which can have a more critical and systematic approach - are essential to ensure doctors and other health professionals have the information they need on drugs.

The authors, based in Denmark, compared the results of 24 pairs of reviews conducted by different people on the same drugs. Compared to reviews supported by the pharmaceutical industry, reviews undertaken by the Cochrane Collaboration an independent body were of a higher quality and were more likely to address the potential for bias in the review.

Of seven industry-supported reviews, all recommended the experimental drug without reservation, whilst none of the corresponding Cochrane reviews reached the same conclusion. Six of the eight Cochrane reviews analysed had reservations about the quality or relevance of the trials or their findings and two of them noted that the effect decreased with increasing number of patients in the trial. Seven mentioned higher cost of the experimental drug as a problem. In contrast, none of the industry-supported reviews mentioned higher cost as a problem, and two claimed that the experimental drug was cost-effective.

The researchers also found that the reviews with not-for-profit support or no support had similarly cautious conclusions as the Cochrane reviews.