Psychonautics refers both to a methodology for describing and explaining the subjective effects of altered states of consciousness, including those induced by meditation or mind-altering substances, and to a research cabal in which the researcher voluntarily immerses themselves into an altered mental state in order to explore the accompanying experiences.

Hallucinogens are a large and diverse class of psychoactive drugs that can produce altered states of consciousness characterized by major alterations in thought, mood, and perception as well as other changes. Most hallucinogens can be categorized as either being psychedelics, dissociatives, or deliriants.