Concord Prison Experiment
The Concord Prison Experiment was designed to evaluate whether the experiences produced by the psychoactive drug psilocybin, derived from psilocybin mushrooms, combined with psychotherapy, could inspire prisoners to leave their antisocial lifestyles behind once they were released. How well it worked was to be judged by comparing the recidivism rate of subjects who received psilocybin with the average for other Concord inmates.
The experiment was conducted between 1961–1963 in Concord State Prison, a maximum-security prison for young offenders, in Concord, MA by a team of Harvard University researchers under the direction of Timothy Leary, which included Michael Hollingshead, Dr. Allan Cohen, Dr. Alfred Alschuder, Dr. George Litwin, Dr. Ralph Metzner, Dr. Gunther Weil, and Dr. Ralph Schwitzgebel, with Dr. Madison Presnell as the medical and psychiatric adviser. The original study involved the administration of psilocybin to assist group psychotherapy for 32 prisoners in an effort to reduce recidivism rates.
Records at Concord State Prison suggested that 64 percent of the 32 subjects would return to prison within six months after parole. However, after six months, 25 per cent of those on parole had returned, six for technical parole violations and two for new offenses. Few short-term projects with prisoners have been effective to even a minor degree. In addition, the personality test scores indicated a measurable positive change when pre-psilocybin and post-psilocybin results were compared.
The results of this experiment have been largely contested by a follow-up study, citing several problems including differences in the length of time after release that the study group versus the control group were compared, and other methodology factors including the difference between subjects re-incarcerated for parole violations versus imprisoned for new crimes. This study concluded that only a statistically slight improvement could be shown (as opposed to the radical improvement originally reported). In his interview within the study, Leary expressed that the major lesson of the Concord Prison experiment was that the key to a long-term reduction in overall recidivism rates might be the combination of the pre-release administration of psilocybin-assisted group psychotherapy with a comprehensive post-release follow-up program modeled on Alcoholics Anonymous groups to offer support to the released prisoners. The study concluded that whether a new program of psilocybin-assisted group psychotherapy and post-release programs would significantly reduce recidivism rates is an empirical question that deserves to be addressed within the context of a new experiment. 
- Doblin, Rick Dr. Leary's Concord Prison Experiment: A 34 Year Follow-Up Study
- Metzner, Ralph Reflections on the Concord Prison Experiment and the Follow-Up Study
- Hollingshead, Michael The Man Who Turned on the World