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A “hallucination” is defined as a false perception that has no basis in the external environment. The term is derived from the Latin “to wander in mind.” Hallucinations differ from illusions, which are distorted perceptions of objects based in reality. Although the term psychedelic has been used for years to refer to the recreational and nonmedical effects of hallucinogens, other terms, such as entheogen and entactogen, frequently appear in discussions. Entheogens are “substances that generate the god or spirit within,” and entactogens create an awareness of “the touch within.”50 These terms all refer to the same xenobiotics, used with differing intent or in varying settings.

Hallucinogens are a diverse group of xenobiotics that alter and distort perception, thought, and mood without clouding the sensorium. Hallucinogens are categorized by their chemical structures and are further divided into natural and synthetic members of each family. The major structural classes of hallucinogens include the lysergamides, tryptamines (indolealkylamines), amphetamines (phenylethylamines), arylhexamines, cannabinoids, harmine alkaloids, belladonna alkaloids, and tropane alkaloids. In addition, there are several unclassified hallucinogens, such as Salvia divinorum, nutmeg (Myristica fragrans), kratom (Mitragyna speciose), and kava kava (Piper methysticum). This chapter focuses on lysergamides, tryptamines, phenylethylamines, and the aforementioned “unclassified” hallucinogens. The other classes are found in Chaps. 71, 73, 74, and 83 (Table 79–1).

TABLE 79–1Structural Classifications of Hallucinogens

Hallucinogens have been used for thousands of years by many different cultures, largely during religious ceremonies. The ancient Indian holy book, Rig-Veda, written more than 3,500 years ago, describes a sacramental substance called Soma both as a god and as an intoxicating substance. Although debated for many years, the source of Soma is now believed to be an extract of the mushroom Amanita muscaria.121,129 The Aztecs used the psilocybin-containing mushroom Psilocybe mexicana, termed “teonanacatl” (flesh of the gods), and the lysergic acid amide-containing morning glory plant, Turbina corymbosa, known as “Ololiuqui” in their religious ceremonies. The Native American Church in the United States uses peyote in religious ceremonies.28,31,116 In South America, ayahuasca, a tea made of dimethyltryptamine-containing plants (eg, Psychotria viridis), ...

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