Psychedelic drugs, also known as hallucinogenic drugs or simply hallucinogens, are a group of substances that are usually used recreationally to change and enhance sensory perceptions, thought processes, and energy levels, and to facilitate spiritual experiences. They include chemicals, such as LSD, and AL-LAD   4-HO MET blotters plants, such as peyote.

Psychedelics have also been used experimentally to mimic psychosis and to exert mind control, although they have not been found to be particularly effective in doing either. They were used in psychotherapy in the 1960s, but this was halted for mainly political reasons until quite recently. Psychological research has since revived the use of psychedelics in experimental psychological treatment.