First research since the 1970s to administer a classic psychedelic (psilocybin) to drug naïve participants. Psilocybin led to profound experiences that 67% of participants rated as among the top 5 most meaningful experiences of their lifetime. The single psilocybin session led to positive changes in moods, attitudes, and behavior for 14 months (and possibly longer), with 64% indicating the experience increased well-being or life-satisfaction. The study also established the safety of high dose psilocybin administration.