In this episode of the Drug Science podcast, Professor Nutt is joined by an old friend who he has known for 35 years. Professor Roland Griffiths is a researcher based at Johns Hopkins Center for Psychedelic and Consciousness Research, who has examined a wide range of psychotropic substances over the years. Here they discuss psilocybin and mystical-type experiences, caffeine, tobacco addiction and William James and the Varieties of Religious Experience.