APA Dictionary of Psychology

n. a hallucinogen derived from the peyote cactus and long used by indigenous peoples of the southwestern United States and Central America as part of certain religious ceremonies. Its effects often include nausea and vomiting as well as visual hallucinations involving lights and colors; they have a slower onset than those of LSD and usually last 1 to 2 hours. Mescaline is the oldest classic hallucinogen known to Western science; its pharmacology was defined in 1896, and its structure was verified by synthesis in 1919. It is a substituted phenylethylamine, and its likely mechanism of action is via serotonin and dopamine receptors. Mescaline is classified by the U.S. Drug Enforcement Administration as a Schedule I controlled substance (see scheduled drug).