Hallucinogen

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

Cannabinoids (CB1 receptor agonists) like THC, nabilone, and JWH-018

Others like carbogen, hallucinogenic bolete mushrooms, and nutmeg

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.