Psilocybin, a naturally occurring hallucinogen, is the main psychoactive component of psilocybe and other hallucinogenic mushrooms (so called “magic mushrooms”). Like other classic hallucinogens, such as d-lysergic acid diethylamide (LSD) and mescaline, psilocybin exerts its psychoactive effects through a sub-type of serotonin receptors (called 5-HT2a) in the brain. In some cultures, psilocybin has historically been used in religious contexts -- likely for millennia. Psilocybin has a number of effects, including changes in perception, cognition, affect, and decision-making. Clinical research on psilocybin dates back to at least the 1950s, with variable effects on the perceived affective character of the experience. Research on psilocybin administration in humans has occurred in psychotherapeutic contexts in terminally ill cancer patients dating back to the 1970s and continues today. A surprising new study reveals that, under specific conditions, acute exposure to psilocybin can elicit long-lasting positive changes and increases in mystical-type experience.