For 6 years, Dr Robin Carhart-Harris has explored the brain effects of drugs such as LSD, psilocybin (magic mushrooms) and MDMA, completing some of the first brain imaging studies of these drugs. Most recently, he has been running a clinical trial looking at the potential of psilocybin to treat depression. In this short lecture, he describes the history of psychedelics, explains how they work, and explores their therapeutic potential.