Collective term for drugs with hallucinogenic effect. According the WHO definition hallucinogens are "chemical agents that induce alterations in perception, thinking, and feeling which resemble those of the functional psychoses without producing the gross impairment of memory and orientation characteristics of the organic syndromes."
Examples include LSD, DMT, psilocybin, mescaline, MDA, MDMA or ecstasy, and phencyclidine (PCP).