The use of animal tests in drug development is fundamentally flawed, according to new evidence presented at the BA (British Association for the Advancement of Science) Festival of Science in York on Friday.

As a result, many animal studies “overstate how effective drugs really are”, said Malcolm Macleod, a consultant neurologist at Edinburgh university. These drug candidates then fail to work when given to humans in clinical trials – and could even put patients’ health at risk. The main issue is experimenters’ unconscious bias. Researchers do not routinely divide animals at random into treatment and control groups and, when they analyse results, they know which animals have been treated and which have not.