The term 'psychedelic' was coined, in 1954, in response to Aldous Huxley's first mescaline trip. 'Psychedelic' emerged from a correspondence between Huxley and Humphry Osmond, the psychiatrist who supplied him with the mescaline he took at his home in the Hollywood Hills in May 1953. (Huxley thought the spelling should be 'psychodelic' and persisted with it, to little avail.) His essay on the experience, The Doors of Perception (1954), kickstarted the psychedelic era. The terms in vogue for these drugs at that time, such as 'psychotomimetic' and 'hallucinogen', had emerged from psychiatry and connected their effects to mental disorders. The mescaline experience, Huxley argued, was not a psychotic episode but a transcendent state, a communion with the 'Mind-at-Large'.
The term psychedelic was created by English psychologist and researcher Humphry Osmond. Osmond derived the term from the Greek words for mind or soul (psyche) and show (deloun) to describe the effect LSD had on the mind. A psychedelic experience is characterized by changes of perception, synesthesia, altered states of awareness or focused consciousness, variation in thought patterns, trance or hypnotic states, mystical states, and other mind alterations. For some people, the psychedelic experience can invoke newly formed understandings, revelations, or enlightenment.
Psychedelic experiences are typically, though not necessarily, produced by the use of psychedelic drugs. Psychedelic drugs are compounds which (when consumed) produce psychedelic effects and include many tryptamines and ergotamines. Typically, these drugs are believed to produce psychedelic effects by activation of a subtype of serotonin receptors (5-HT2A) in the brain.Although the term "hallucinogen" is often used interchangeably with "psychedelic," the former term best describes a substance that causes a user to perceive something that is not objectively present. By contrast, the term "psychedelic" best describes a substance that invokes a change in the perception of things that are objectively present.