The practice of medicine is based on evidence. We need this evidence base to be complete, and of the highest quality, so that we can make the right decisions, but at present, drug companies produce most of the evidence we use. There is no doubt that these companies have a conflict of interest when they conduct trials: they want to sell their products, and so naturally they want a positive result from the trials they sponsor. But there is now good evidence from systematic reviews, meta-analyses, and case studies that this conflict of interest results in bad evidence, which distorts medical decision making and so harms patients.

We will start with a tangible story, from a single field. Rochon1 analysed the literature on non-steroidal anti-inflammatory drugs (NSAIDs), and found all the studies that had ever been published where one NSAID was compared to another. In every single trial, the sponsoring company’s …