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A. Classification of Hallucinogens and Hallucinogen-Related Disorders

It is difficult to define hallucinogens, given that drugs that can produce hallucinations are so diverse in chemical structure and mechanism/s of action. Many psychoactive drugs can induce hallucinations if given at high enough doses. For example, nicotine and even alcohol have been associated with hallucinations, even though these effects are not characteristic or desired. This chapter focuses on drugs that induce changes in thought, perception, and mood to a much greater extent than their other effects. In this chapter, hallucinogens are grouped into three categories: serotonergic (tryptamine-like and phenethylamine-like), N-methyl-D-aspartate (NMDA) antagonist, and other. In addition to the drugs described earlier, new designer phenethylamine and tryptamine drugs and other newer entities are being identified on the street every year with unknown purity and safety profiles (Elie et al, 2013; Kobayashi et al, 2010).

The distinction between MDMA and "Ecstasy" should be noted. Pills sold as "Ecstasy" often contain MDMA, but also often contain additional psychoactive substances and impurities. The dose of MDMA can vary widely between pills, and sometimes "Ecstasy" does not contain MDMA at all (Vogels et al, 2009; Morefield et al, 2011). Considering this, recreational "Ecstasy" is the most harmful of the serotonergic hallucinogens because of its unknown potency and purity.

B. Use of Hallucinogens

There is a long history of the use of hallucinogenic plants (such as Salvia divinorum, psilocybin, mescaline, ibogaine, and the dimethyltryptamine [DMT]-containing brew ayahuasca) by humans. Ceremonial hallucinogenic plant use can be found in cultures on most continents and in the histories of all the world's major religions (Schultes et al, 2001). As described later in further detail hallucinogens are used recreationally to produce alterations in perception, as a means of attaining altered states of consciousness.

In the past century, a number of hallucinogens such as LSD and MDMA have been synthesized. These compounds have been characterized as extremely important to scientific research and clinical use at one extreme, and as being dangerous addictive compounds with no accepted medical use at the other extreme.

C. Maladaptive Patterns of Hallucinogen Use

Hallucinogen-related disorders are classified into two categories: hallucinogen use disorders and hallucinogen-induced disorders. Psychopathology in a patient may be due to hallucinogen use, a psychiatric diagnosis, or an interaction between the two. The Diagnostic and Statistical Manual of Mental Disorders, 5th edition (DSM-5) defines maladaptive patterns of drug use as involving tolerance and withdrawal. Tolerance develops rapidly to some effects of some hallucinogens but not to others. For example, tolerance develops in recreational users of LSD and "Ecstasy" but not in users of DMT. Discontinuation of most of these compounds does not appear to be associated with a withdrawal syndrome. Acute withdrawal is observed among regular users of "Ecstasy", but because of the varying and ...

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