Most treatments are initially tested on animals for several reasons. Firstly, animal studies provide a degree of environmental and genetic manipulation rarely feasible in humans.1 Secondly, it may not be necessary to test new treatments on humans if preliminary testing on animals shows that they are not clinically useful. Thirdly, regulatory authorities concerned with public protection require extensive animal testing to screen new treatments for toxicity and to establish safety. Finally, animal studies provide unique insights into the pathophysiology and aetiology of disease, and often reveal novel targets for directed treatments. Yet in a systematic review reported in this week's BMJ Perel and colleagues find that therapeutic efficacy in animals often does not translate to the clinical domain.2

The authors conducted meta-analyses of all available animal data for six interventions that showed definitive proof of …