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The therapeutic use of psychedelic substances was concomitant with the discovery of LSD and Mescaline after the Second World War. These therapeutic uses initially concerned “the accompaniment” of psychotherapies, the treatment of addictions (alcohol, then opiates), and, because of their anxiolytic and antidepressive capacities, the management of post-traumatic psychological disorders, resistant depressions, obsessive and psychosomatic pathologies (pain, migraines, etc.) and support for the end of life. With the prohibition of the medical use of these substances during the 1960s (following their classification in the international conventions for the prohibition of narcotics), the research on neurophysiological and therapeutic activities was also stopped. A few rare experiments were continued during the 1980s (MDMA, ibogaine), but it is only since 1994 (authorization in the USA of the resumption of treatments with the MDMA at the end of life, then in PTSD) that research has resumed in most Western countries, except in France. At the same time, since the end of the 1990s, there has been a return to a reflection on the ancient use of psychedelic plants as part of the ethnographic interest in shamanism. Today, many scientific foundations (MAPS, The Beckley Foundation, Heffter Research Institute, etc.) and universities are studying the therapeutic effects of psychedelic substances, and clinical and neurobiological studies are gradually being resumed. The indications concern the management of addictions, the treatment of psychotraumatic disorders, in connection with psychotherapies, and all areas relating to anxiety and depression, as well as autistic states and “resistant schizophrenia” to conventional treatments.