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A “hallucination” may be defined as a false perception that has no basis in the external environment. The term is derived from the Latin term meaning “to wander in mind.” While the term “psychedelic” has been used for years to refer to the recreational and nonmedical effects of hallucinogens, other terms, like entheogen and entactogen, frequently appear in Internet discussions. Entheogens are “substances which generate the god or spirit within,” while entactogens create an awareness of “the touch within.”41 These terms all refer to the same xenobiotics, used with differing intent or in varying settings. Hallucinations differ from illusions, which are distorted perceptions of objects based in reality.

Hallucinogens are a diverse group of xenobiotics that alter and distort perception, thought, and mood without clouding the sensorium. Hallucinogens can be categorized by their chemical structures, and 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 the tropane alkaloids. In addition, there are several unique hallucinogens, such as Salvia divinorum, nutmeg, kratom, and kava kava. This chapter focuses on lysergamides, tryptamines, phenylethlyamines, and the unique hallucinogens. More on the other classes can be found in Chaps. 73, 76, 77, 78, and 86.

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 3500 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.101,108 The Aztecs used the psilocybin-containing teonanacatl (flesh of the gods) and Ololiuqui (morning glory species) in their religious ceremonies. To this day, the Native American Church in the United States uses peyote in religious ceremonies.

From medieval times through recent years, several large-scale epidemics of vasospastic ischemia, gangrene, and hallucinations (collectively called ergotism) have resulted from Claviceps purpurea contamination of cereal crops.136 The hallucinations from Claviceps ingestion are attributed to the ergot alkaloid lysergic acid amide from which lysergic acid diethylamide (LSD) was chemically synthesized. Claviceps purpurea has been suggested, but subsequently disproved, as the cause of the mass hysteria leading up to the Salem witch trials. Many of these adverse effects after ingestion of C. purpurea have been attributed to the serotonergic agonist effects of the ergot alkaloids (Chap. 54).38

Synthetic hallucinogen use is often said to have begun in 1938 when Albert Hofmann, a Swiss chemist, synthesized LSD while performing extensive research on the medicinal uses of ergot alkaloids derived from the fungus, C. purpurea. Five years later, LSD was “tested” when Hofmann exposed himself in his laboratory and subsequently developed hallucinations.63,...

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