Psychedelic therapy refers to the proposed use of psychedelic drugs, such as psilocybin, MDMA, LSD, and ayahuasca, to treat mental disorders. As of 2021, psychedelic drugs are controlled substances in most countries and psychedelic therapy is not legally available outside clinical trials, with some exceptions.

Lysergic acid diethylamide, commonly known as LSD, and known colloquially as acid or lucy, is a potent psychedelic drug. Effects typically include intensified thoughts, emotions, and sensory perception. At sufficiently high dosages, LSD manifests primarily mental, visual, and auditory hallucinations. Dilated pupils, increased blood pressure, and increased body temperature are typical.