Human hallucinogen use precedes written history, and has shaped many lives and cultures throughout time. These drugs can be quite different from each other, however, and are commonly grouped into three major categories: psychedelics, dissociatives, and deliriants.

Psychedelics

Examples: cannabis (marijuana), methylenedioxymethamphetamine (MDMA, ecstacy), lysergic acid diethylamide (LSD), psilocybin mushrooms

The category psychedelic drug is a blanket term for many chemical compounds with a variety of effects. The three sub-groups of psychedelics are cannabinoids, empathogens (also known as entactogens), and serotonergics. The underlying similarities between all three types of psychedelic drugs are that they produce changes in consciousness that are generally unfamiliar, while other classes of drugs such as stimulants or depressants give rise to familiar, if greatly magnified, states of mind.

Cannabinoid drugs, which work as antagonists of cannabinoid receptors in the brain, are named after the prototypical drug in this class, cannabis (also known as marijuana), which contains the psychoactive compound tetrahydrocannabinol (THC). Effects of cannabinoids vary between dosages, users, and the types and amounts of particular compounds (different cannabis strains contain differing ratios of many different cannabinoid compounds). Users commonly report mild euphoria, senses of well-being, increased awareness of external sensations, increased hunger, and disruption of linear memory processes.

Empathogens are a class of psychedelics that release serotonin in the brain and derive their name from one of their major effects: increased feelings of empathy. The best-known drug in this class is MDMA, although several similar compounds exist as well. Users generally report heightened feelings of love, openness, euphoria, and overall enhancement of sensory experiences.

Serotonergic drugs are so named due to their activity as agonists of a specific serotonin receptor (5-HT2A) in the brain. Drugs in this class include LSD, DMT, psilocybin (the psychoactive compound in hallucinogenic mushrooms), and phenethylamines such as mescaline and 2C-B. Users of these drugs experience intense, fundamental alterations of perception, including synesthesia, visual and auditory hallucinations, and unusual thought patterns or emotional responses.

Dissociatives

Examples: ibogaine, phencyclidine (PCP), ketamine, dextromethorphan (DXM)

Dissociative hallucinogens, including ibogaine, PCP, ketamine, and DXM (at dosages many times larger than its use as a cough suppressant), work as antagonists of the N-methyl-D-aspartate (NMDA) receptors in the brain. While many of these drugs produce perceptual alterations similar to the psychedelic drugs listed above, the distinguishing features of dissociatives are feelings of depersonalization, or being disconnected from ones body. Derealization, or the sensation that ones surrounding environment is somehow not real, is also a characteristic of these drugs.

Deliriants

Examples: atropine, scopolamine (hyoscine), diphenhydramine (benadryl)

Deliriants are a class of psychoactive drug that generally block the neurotransmitter acetylcholine from binding to receptors in the brain and central nervous system. As recreational drugs, deliriants produce vivid and generally very unpleasant hallucinations in addition to potentially dangerous side-effects. While users of psychedelics and dissociatives often report having euphoric, spiritual experiences, users of deliriants almost universally report unpleasant effects and have no desire to use these drugs again.

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The Three Types of Hallucinogens: Psychedelics ...