Psilocybin ( sy-lə-SY-bin) is a naturally occurring psychedelic prodrug compound produced by more than 200 species of mushrooms, collectively known as psilocybin mushrooms.
In 1959, the Swiss chemist isolated the active principle psilocybin from the mushroom Psilocybe mexicana. Hofmann's employer Sandoz marketed and sold pure psilocybin to physicians and clinicians worldwide for use in psychedelic psychotherapy. Although the increasingly restrictive drug laws of the late 1960s curbed scientific research into the effects of psilocybin and other hallucinogens, its popularity as an entheogen (spirituality-enhancing agent) grew in the next decade, owing largely to the increased availability of information on how to cultivate psilocybin mushrooms. The intensity and duration of the effects of psilocybin are variable, depending on species or cultivar of mushrooms, dosage, individual physiology, and set and setting, as was shown in experiments led by at Harvard University in the early 1960s.