Many societies and civilizations have used hallucinogenic substances in their ritual practices. These substances expand perceptions, lead to visions and changes in consciousness. The traditional practices of Shamana, which are inserted in their cultures and beliefs, respond to preventive and curative demands. Do these psychedelic substances have or could they be of therapeutic interest? That is the subject of this thesis. The first part is intended to clarify the definition of psychedelic and hallucinogens. At controlled doses, these substances would explore the unconscious and promote positive introspections. Psychedelic is poorly known molecules, known as vulgarily hallucinogens, confounded with drugs while far from any phenomenon of drug abuse. The proposed classification makes it possible to clarify this situation. Three psychedelic items will be analyzed: Ayahuasca, hallucinogenic Amerindian ethnic groups in the Amazon forest, practised for millennia to the present day. The most famous LSD, obtained by synthesis from rye ergot derivatives. And finally ketamine, the most promising, anesthetic used in surgical operations, is a low-dose psychedelic. These extracts of plants or substances have already been subjected to numerous clinical work for over 60 years. The synthesis of these different therapeutic properties that would have these substances is presented. It shows their therapeutic interest in the treatment of diseases such as neurosis, addictions, depression, etc. This work coincided in the 1960s with the hippie movement, and then was interrupted and these substances were classified as narcotic. This limited and made it difficult for any new clinical assessment. However, clinical trials were resumed in the 1990s. This research generally shows the interest of psychedelic therapeutic therapeutic when accompanied by medical monitoring. Finally, a discussion presents assumptions on the reasons for the non-development of these therapeutic therapeutic and personal interest in both a therapeutic and also holistic approach for a better self-knowledge.