Hallucinogens, also known as psychedelics, entheogens, or historically as psychotomimetics, are a broad and diverse class of psychoactive drugs that can induce altered states of consciousness characterized by marked changes in perception, mood, cognition, and self-experience, along with a range of other psychological alterations. Hallucinogens are often categorized as either being psychedelics, dissociatives, or deliriants, but not all hallucinogens fall into these three classes.
Types and examples
Types and examples of hallucinogens include the following:
Psychedelics (5-HT2A receptor agonists) like LSD, psilocybin, mescaline, and DMT Dissociatives (NMDA receptor antagonists) like ketamine, PCP, DXM, and nitrous oxide Deliriants (antimuscarinics) like scopolamine, diphenhydramine, and trihexyphenidyl κ-Opioid receptor agonists like salvinorin A, pentazocine, and levorphanol GABAA receptor agonists like muscimol and gaboxadol Oneirogens (unknown mechanism) like ibogaine and harmaline Others like hallucinogenic bolete mushroom
Definition
Characteristics Leo Hollister gave five criteria for classifying a drug as hallucinogenic. This definition is broad enough to include a wide range of drugs and has since been shown to encompass a number of categories of drugs with different pharmacological mechanisms and behavioral effects. Richard Glennon has thus given an additional two criteria that narrow the category down to classical hallucinogens. Hollister's criteria for hallucinogens were as follows:
in proportion to other effects, changes in thought, perception, and mood should predominate; intellectual or memory impairment should be minimal; stupor, narcosis, or excessive stimulation should not be an integral effect; autonomic nervous system side effects should be minimal; and addictive craving should be absent. Glennon's additional criteria for classical hallucinogens are that the drugs in question must also:
bind at 5-HT2 serotonin receptors; and be recognized by animals trained to discriminate the drug DOM from vehicle.
Nomenclature and taxonomy Most hallucinogens can be categorized based on their pharmacological mechanisms as psychedelics (which are serotonergic), dissociatives (which are generally antiglutamatergic), or deliriants (which are generally anticholinergic). However, the pharmacological mechanisms of some hallucinogens, such as salvinorin A and ibogaine, do not fit into any of those categories. Entactogens and cannabinoids are also sometimes considered hallucinogens. Nonetheless, while the term hallucinogen is often used to refer to the broad class of drugs covered in this article, sometimes it is used to mean only classical hallucinogens (that is, psychedelics). Because of this, it is important to consult the definition given in a particular source. Because of the multi-faceted phenomenology brought on by hallucinogens, efforts to create standardized terminology for classifying them based on their subjective effects have not succeeded to date. Classical hallucinogens or psychedelics have been described by many names. David E. Nichols wrote in 2004:
Many different names have been proposed over the years for this drug class. The famous German toxicologist Louis Lewin used the name phantastica earlier in this century, and as we shall see later, such a descriptor is not so farfetched. The most popular names—hallucinogen, psychotomimetic, and psychedelic ("mind manifesting")—have often been used interchangeably. Hallucinogen is now, however, the most common designation in the scientific literature, although it is an inaccurate descriptor of the actual effects of these drugs. In the lay press, the term psychedelic is still the most popular and has held sway for nearly four decades. Most recently, there has been a movement in nonscientific circles to recognize the ability of these substances to provoke mystical experiences and evoke feelings of spiritual significance. Thus, the term entheogen, derived from the Greek word entheos, which means "god within", was introduced by Ruck et al. and has seen increasing use. This term suggests that these substances reveal or allow a connection to the "divine within". Although it seems unlikely that this name will ever be accepted in formal scientific circles, its use has dramatically increased in the popular media and on internet sites. Indeed, in much of the counterculture that uses these substances, entheogen has replaced psychedelic as the name of choice and we may expect to see this trend continue. Robin Carhart-Harris and Guy Goodwin write that the term psychedelic is preferable to hallucinogen for describing classical psychedelics because of the term hallucinogen's "arguably misleading emphasis on these compounds' hallucinogenic properties." However, others such as Nichols disagree and feel that the term psychedelic should be reserved to described serotonergic psychedelics specifically as it has been historically. Certain hallucinogens are designer drugs, such as those in the 2C and 25-NB (NBOMe) families. A designer drug is a structural or functional analog of a controlled substance (hallucinogenic or otherwise) that has been designed to mimic the pharmacological effects of the original drug while at the same time avoid being classified as illegal (by specification as a research chemical) and/or avoid detection in standard drug tests.
Effects by type Different classes of hallucinogens have different mechanisms of action and effects.
Psychedelics
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