Timothy Francis Leary (October 22, 1920 – May 31, 1996) was an American psychologist and writer known for advocating the exploration of the therapeutic potential of psychedelic drugs under controlled conditions.
As a clinical psychologist at Harvard University, Leary conducted experiments under the Harvard Psilocybin Project in 1960–62 (LSD and psilocybin were still legal in the United States at the time), resulting in the Concord Prison Experiment and the Marsh Chapel Experiment. The scientific legitimacy and ethics of his research were questioned by other Harvard faculty because he took psychedelics together with research subjects and pressured students in his class to take psychedelics in the research studies. Leary and his colleague, Richard Alpert (who later became known as Ram Dass), were fired from Harvard University in May 1963. National illumination as to the effects of psychedelics did not occur until after the Harvard scandal.Leary believed that LSD showed potential for therapeutic use in psychiatry. He used LSD himself and developed a philosophy of mind expansion and personal truth through LSD. After leaving Harvard, he continued to publicly promote the use of psychedelic drugs and became a well-known figure of the counterculture of the 1960s. He popularized catchphrases that promoted his philosophy, such as "turn on, tune in, drop out", "set and setting", and "think for yourself and question authority". He also wrote and spoke frequently about transhumanist concepts involving space migration, intelligence increase, and life extension (SMI²LE), and developed the eight-circuit model of consciousness in his book Exo-Psychology (1977). He gave lectures, occasionally billing himself as a "performing philosopher".During the 1960s and 1970s, he was arrested often enough to see the inside of 36 prisons worldwide. President Richard Nixon once described Leary as "the most dangerous man in America".