A hallucinogen is a psychoactive agent that often or ordinarily causes hallucinations, perceptual anomalies, and other substantial subjective changes in thought, emotion, and consciousness that are not typically experienced to such degrees with other drug classifications. The common classifications for hallucinogens are psychedelics, dissociatives and deliriants. Although hallucinogens all can induce altered states of consciousness with some overlap in effects, there are quantifiable as well as vast qualitative differences in the induced subjective experiences between the different classes of hallucinogens due to differing and distinct pharmacological mechanisms.
