Classical hallucinogens can be divided into 2 chemical classes. Tryptamines include psilocybin (present in several mushroom genera) and the semisynthetic D-lysergic acid diethylamide (LSD). Phenethylamines include mescaline (the active constituent of peyote). Classical hallucinogen effects are primarily mediated by agonist activity at 5-HT2A receptors. Other classes of pharmacologically unrelated substances have sometimes been labeled as “hallucinogens,” including cannabis, 3,4-methylenedioxymetham-phetamine, dissociative anesthetics (e.g., phencyclidine), and anticholinergic drugs (e.g., scopolamine). In this entry, the term hallucinogen will refer exclusively to classical hallucinogens.


Physiological symptoms may include dizziness, weakness, tremors, nausea, drowsiness, paresthesia, blurred vision, dilated pupils, and increased tendon reflexes. However, these effects vary and are modest in comparison with psychological effects. Perceptual effects can include visual illusions, intensification of colors, proprioceptive changes, and synesthesia. Emotions may be ...

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