Perhaps the most influential and rigorous of these early studies was the Good Friday experiment, conducted in 1962 by Walter Pahnke, a psychiatrist and minister working on a Ph.D. dissertation under Leary at Harvard. In a double-blind experiment, twenty divinity students received a capsule of white powder right before a Good Friday service at Marsh Chapel, on the Boston University campus; ten contained psilocy- bin, ten an active placebo (nicotinic acid). Eight of the ten students receiving psilocybin reported a mystical experience, while only one in the control group experi- enced a feeling of “sacredness” and a “sense of peace.” (Telling the subjects apart was not difficult, rendering the double-blind a somewhat hollow conceit: those on the placebo sat sedately in their pews while the others lay down or wandered around the chapel, muttering things like “God is everywhere” and “Oh, the glory!”) Pahnke concluded that the experiences of eight who received the psilocybin were “indistinguishable from, if not identical with,” the classic mystical experiences reported in the literature by William James, Walter Stace, and others.

Since the 1990s, there has been a renewal of scientific research into the potential medical and psychological therapeutic benefits of psilocybin for treating conditions including obsessive-compulsive disorder, cluster headaches, and anxiety related to terminal cancer. Possession of psilocybin-containing mushrooms has been outlawed in most countries, and it has been classified as a scheduled drug by many national drug laws.