Nutt said: "The decision to outlaw these drugs was based on their perceived dangers, but in many cases the harms have been overstated and are actually less than many legal drugs such as alcohol.
"The laws have never been updated despite scientific advances and growing evidence that many of these drugs are relatively safe. And there appears to be no way for the international community to make such changes."
The paper argues that the illegal status of psychoactive drugs makes research into their mechanisms of action and potential therapeutic uses, for example in depression and post-traumatic stress disorder (PTSD), difficult.
"This hindering of research and therapy is motivated by politics, not science. It’s one of the most scandalous examples of scientific censorship in modern times," said Nutt.