Answer: The Good Friday experiment was a demonstration of the entheogenic properties of psilocybin.
Many psychedelic drugs, such as LSD or psilocybin, are also called entheogens, drugs that are able to create a strong sense of religion in a person after even a single exposure. In 1962, researcher Timothy Leary and the physician / minister Walter Pahnke, both based out of Harvard, conducted an experiment in conjunction with the Harvard Divinity School. In the experiment, a group of 20 volunteers from the Andover Newton Theological School were randomly assigned into one of two groups. One half would receive a dose of 30 milligrams psilocybin, while the other half would receive a dose of niacin, an active placebo that causes a physiological reaction similar to that of psilocybin. Neither group was aware of the drug they were given; the experiment was double-blinded. Psilocybin was selected as it is the main psychoactive ingredient found in “magic mushrooms.”
The site of the experiment was the Marsh Chapel on the campus of Boston University. The subjects, after receiving a dosage of either psilocybin or niacin, attended a Good Friday service while under the influence. Afterwards, the subjects were asked about their time. The psilocybin exposed group was more likely to have a mystic experience. They reported a greater influence of the Good Friday service on their life and career path, as well as their interpretation of faith. On the 25 year follow-up, they discovered that the experience influenced them long into the future. One of the subjects in the experimental group who received psilocybin was Huston Smith, who went on to write several textbooks on the topic of comparative religion. The psilocybin subjects unanimously reported that the mystical experience they had was entirely genuine, and many described the Good Friday experiment as one of the high points in their entire religious life.
With this experiment, Pahnke and Leary demonstrated that the mindset of a person and the setting that they are surrounded by both have a strong influence of their experiences under the influence of psilocybin. It is known that with other psychedelics, like LSD, both set and setting influence the subject's experience.
The Good Friday experiment had long reaching implications for the researchers. Timothy Leary lost his faculty position at Harvard. Questions were raised about the ethical publishing of Walter Pahnke's data, since he had failed to report the negative effects of psilocybin on the subjects during the seminar: one was physically restrained from leaving the Marsh Chapel, another was given thorazine, a tranquilizer, to calm him.