Hallucinogens are a class of psychoactive substances that act on the nervous system to alter perception, mood, and various cognitive processes. Hallucinogens represent one of the three major classes of psychoactive substances: the other two are stimulants ("uppers") and depressants ("downers"). However, hallucinogens are claimed to be distinct from stimulants and depressants in that they do not merely amplify or dull existing states of consciousness, but instead produce qualitatively unique states in which the environment and self are perceived in a new fashion.
Notably, hallucinogens are commonly reported to facilitate self-understanding and self-discovery. Hallucinogenic experiences are often compared to non-ordinary forms of consciousness such as lucid dreaming, meditation, religious, mystical or transpersonal experiences, hallucinations, and states of psychosis.
Hallucinogens are divided into three categories: psychedelics (e.g. LSD, psilocybin mushrooms, DMT, etc.), dissociatives (e.g. ketamine, PCP, DXM, etc.), and deliriants (e.g. DPH, scopolamine, datura, etc). Each category is associated with a unique mechanism of action, subjective effects, therapeutic potential, and health risks. It is highly advised to use harm reduction practices when using these substances.
List of hallucinogens