Psychedelics, Dissociatives and Deliriants

A hallucinogen is a psychoactive agent which can cause hallucinations, perceptual anomalies, and other substantial subjective changes in thoughts, emotion, and consciousness. The common types of hallucinogens are psychedelics, dissociatives and deliriants. Although hallucinations are a common symptom of amphetamine psychosis, amphetamines are not considered hallucinogens, as they are not a primary effect of the drugs themselves. While hallucinations can occur when abusing stimulants, the nature of stimulant psychosis is not unlike delirium.

L. E. Hollister's criteria for establishing that a drug is hallucinogenic are as follows:

A debate persists on criteria which would easily differentiate a substance which is 'psychedelic' from one 'hallucinogenic'. Sir Thomas Browne in 1646 coined the term 'hallucination' from the Latin word "alucinari" meaning "to wander in the mind". The term 'psychedelic' is derived from the Ancient Greek words psychē (ψυχή, "mind") and dēloun (δηλοῦν, "to make visible, to reveal"), or "mind-revealing".

'A hallucinogen' and 'a psychedelic' may refer correctly to the same substance. 'Hallucinations' and 'psychedelia' may both refer to the same aspects of subjective experience in a given instance. The term psychedelia carries an added reference to psychedelic substance culture, and 'psychedelics' are considered by many to be the 'traditional' or 'classical hallucinogens' including DMT, Ayahuasca, Psilocybin, Mescaline, and LSD. 'A hallucinogen' in this sense broadly refers to any substance which causes changes in perception or hallucinations, while psychedelics carry a positive connotation of general perceptual enhancement. In contrast to Hollister's original criteria, adverse effects may predominate with some hallucinogens with this application of the term.

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