A psychedelic drug is a drug whose primary action is to alter cognition and perception, typically by agonising serotonin receptors.
Not to be confused with psychoactive drugs, such as stimulants and opioids, which induce familiar states of consciousness, psychedelics tend to affect the mind in ways that result in the experience being qualitatively different from those of ordinary consciousness. The psychedelic experience is often compared to non-ordinary forms of consciousness such as trance, meditation, yoga, religious ecstasy, dreaming and even near-death experiences. With a few exceptions, most psychedelic drugs fall into one of the three following families of chemical compounds; tryptamines, phenethylamines, and lysergamides.
Many psychedelic drugs are illegal worldwide under the UN conventions unless used in a medical or religious context. Despite these regulations, recreational use of psychedelics is common.
The term psychedelic is derived from the Greek words ψυχή (psyche, "soul, mind") and δηλείν (delein, "to manifest"), hence "soul-manifesting", the implication being that psychedelics can access the soul and develop unused potentials of the human mind. The word was coined in 1956 by British psychiatrist, Humphry Osmond, the spelling loathed by American ethnobotanist, Richard Schultes, but championed by the American psychologist, Timothy Leary.