Psychedelics and Psychoactive Research Glossary

This glossary explains words you will meet across the Psychedelics & Psychoactive Research library. It is information only: it gives no amounts, sourcing or advice to use any substance. Definitions are kept short; the technical note adds the precise point researchers or regulators make. Laws change and nothing here is legal advice. If you or someone else is in danger after taking any substance, call 911 (US) or your local emergency number; US Poison Help is 1-800-222-1222; in a US mental health crisis call or text 988.

Terms are in alphabetical order. For how evidence is labeled in this library, see how to read a psychedelic clinical trial and safety and legal basics.

5-HT2A receptor

A docking site for the brain messenger serotonin. Classic psychedelics mainly act here. [1] Technical note: Written 5-hydroxytryptamine receptor type 2A. Naming the receptor does not by itself explain a drug's effects. [1] Owning guide: serotonin receptors in plain language

Adulteration

When a product contains other substances than its label says, often without the buyer knowing. [2] Technical note: NIDA reports drugs sold as MDMA have contained other drugs, including synthetic cathinones and opioids such as fentanyl. [2] Owning guide: contamination and adulteration

Adverse event

Any unwanted medical event during a study or treatment, whether or not the drug caused it. [3] Technical note: In one review of trials, only 23.5% described systematic approaches to assessing adverse events. A serious adverse event (SAE) is a more severe category. [3] Owning guide: adverse effects and contraindications

Alkaloid

A nitrogen-containing chemical made by a plant or fungus, many of which act on the body. [4][5] Technical note: Ibogaine is described as an indole alkaloid and mescaline as a naturally occurring alkaloid found in cacti. [4][5] Owning guide: harmala alkaloids and other compounds

Amanita muscaria (fly agaric)

A mushroom in the family Amanitaceae that contains ibotenic acid and muscimol. It is not a psilocybin mushroom. [6][7] Technical note: Accepted name in GBIF: Amanita muscaria (L.) Lam. [6][7] Owning guide: Amanita muscaria profile

Arketamine

One of the two mirror-image forms found in ketamine; the other is esketamine. [8][9] Technical note: Ketamine is a racemic mixture of arketamine and esketamine, according to the Spravato label. Findings on arketamine's antidepressant-like effects cited in our sources come from rodent studies, not people. [8][9] Owning guide: ketamine

Ayahuasca

A traditional Amazonian brew that most often includes Banisteriopsis caapi bark and Psychotria viridis leaves; it contains DMT and MAO inhibitors. [10] Technical note: A review describes these usual ingredients. Ayahuasca is not the same thing as DMT. [10] Owning guide: ayahuasca

Blinding

Keeping participants (and often researchers) unaware of who received the study drug. [11] Technical note: Strong drug effects can break the blind, which can inflate results. [11] Owning guide: how to read a psychedelic clinical trial

Breakthrough Therapy designation

An FDA label meant to speed development of a drug under study. It is not approval. [12][2] Technical note: NIDA notes the FDA gave this designation to some psilocybin formulations and to MDMA, which remain investigational. [12][2] Owning guide: medical approval

Bwiti

A religion practiced in Gabon and, to a lesser extent, other Central African countries, in which iboga is central. [13] Technical note: The tradition is not the same as the isolated compound ibogaine. [13] Owning guide: iboga and Bwiti traditions

Classic psychedelic

A substance, such as psilocybin, LSD or DMT, that mainly acts on serotonin 5-HT2A receptors. [1] Technical note: MDMA and ketamine are not classic psychedelics. [1] Owning guide: classic psychedelics

Cultural keystone species

A plant or animal of exceptional importance to a people's culture. [13] Technical note: Chacruna Institute describes Tabernanthe iboga this way for Bwiti. [13] Owning guide: Indigenous traditions, ethics and conservation

CYP2D6

A liver enzyme that helps the body break down some medicines and ibogaine. [4] Technical note: Differences in this enzyme between people can change blood levels of ibogaine and its main product, noribogaine. [4] Owning guide: how interactions work

Default mode network

A set of connected brain regions linked to self-reflection and mind wandering. [1][14] Technical note: Psychedelics disrupt activity within it, but it is unclear how central this is to any therapeutic effect. [1][14] Owning guide: psychedelics: history and neuroscience

Dissociation

A feeling of being detached from your body, thoughts or surroundings. [8] Technical note: Dissociation is listed as a risk on the esketamine (Spravato) label. [8] Owning guide: dissociation

Dissociative

A drug, such as ketamine or PCP, that makes people feel disconnected from their body and environment. [1] Technical note: They block NMDA receptors, part of the glutamate system. [1] Owning guide: dissociatives

DMT

N,N-dimethyltryptamine, a compound found in plants native to the Amazon rainforest; a synthetic form also exists. [1] Technical note: Not the same as ayahuasca, which is a brew, or as 5-MeO-DMT. [1] Owning guide: DMT: compound guide

Entactogen

A substance, such as MDMA, that mainly increases feelings of closeness; also called an empathogen. [15] Technical note: A 2025 review separates entactogens from hallucinogens and dissociatives. [15] Owning guide: entactogens

Esketamine

A ketamine derivative approved in the US, as the nasal spray Spravato, for treatment-resistant depression in adults. [8][16] Technical note: It is a separate medicine from ketamine, with its own label and restricted program. [8][16] Owning guide: esketamine (Spravato)

Expectancy

What a person expects to happen, which can shape how they respond. [17] Technical note: Expectancy can confound trials of drugs with obvious effects. [17] Owning guide: placebo and expectancy in microdosing

Hallucinogen

An umbrella word some people use for psychedelic and dissociative drugs. [1] Technical note: NIDA notes researchers debate how to describe and classify these drugs. [1] Owning guide: what are psychedelics

hERG channel

A potassium channel in heart cells that helps the heart reset between beats. [4] Technical note: Ibogaine blocks it, delaying repolarization. [4] Owning guide: cardiovascular risks

HPPD

Hallucinogen persisting perception disorder: perceptual changes that linger after use stops or recur. [18] Technical note: A systematic review of treatments found only case reports and small series, so evidence for medicines is unclear. [18] Owning guide: persistent perceptual symptoms

Hyperpyrexia

A dangerous rise in body temperature. [2] Technical note: NIDA describes it as a risk with MDMA, particularly with physical activity or warm settings. [2] Owning guide: MDMA: compound guide

Iboga

The shrub Tabernanthe iboga, whose root bark contains several alkaloids. [19][20] Technical note: The plant is not the same as ibogaine, one of its compounds. [19][20] Owning guide: iboga vs ibogaine

Ibogaine

An isolated alkaloid from the iboga plant, linked to heart-rhythm problems and deaths. [4][13] Technical note: One source describes ibogaine hydrochloride semi-synthesized from Voacanga africana. [4][13] Owning guide: ibogaine: compound guide

Ibotenic acid

A compound in Amanita muscaria that acts on glutamate (NMDA and metabotropic) receptors. [7] Technical note: It is chemically related to muscimol but pharmacologically different. [7] Owning guide: ibotenic acid: compound guide

Ketamine

A compound used as an anesthetic; a dissociative, not a classic psychedelic. [16][1] Technical note: It is not FDA-approved for mental health conditions, though clinics offer it off-label. [16][1] Owning guide: ketamine vs classic psychedelics

LSD

Lysergic acid diethylamide, a semisynthetic compound related to ergot alkaloids. [21][1] Technical note: NIDA describes it as lab-made from chemicals in a fungus that grows on rye. [21][1] Owning guide: LSD: compound guide

MADRS

The Montgomery-Asberg Depression Rating Scale, scored 0 to 60, with higher scores meaning more severe depression. [22] Technical note: Used as the main outcome in several depression trials cited here. [22] Owning guide: psychedelics for major depressive disorder

MAO inhibitor

A substance that blocks monoamine oxidase, an enzyme that breaks down certain chemicals. [10] Technical note: In ayahuasca, MAO inhibitors are part of the brew and matter for medicine interactions. [10] Owning guide: MAO-inhibiting preparations and interactions

MDMA

3,4-methylenedioxymethamphetamine, a lab-made drug with stimulant-like effects. [2] Technical note: NIDA says FDA has not approved it for any medical condition (page dated April 2024). [2] Owning guide: MDMA vs classic psychedelics

Mescaline

A compound found in peyote and some other cacti; it can also be lab-made. [1][5] Technical note: A review describes it as a serotonin 5-HT2A/2C receptor agonist, like other classical psychedelics. [1][5] Owning guide: mescaline: compound guide

Microdosing

Regularly taking very small amounts of a hallucinogenic substance, usually LSD or psilocybin. [12] Technical note: NIDA says research has not established whether it is safe or effective. [12] Owning guide: what is microdosing

Muscimol

A compound in Amanita muscaria that acts as a GABA-type agonist. [7] Technical note: Different from psilocybin, which acts at serotonin receptors. [7] Owning guide: muscimol: compound guide

Mystical experience

A change in perception that may include awe and a feeling of unity. [12] Technical note: Researchers are unclear whether it is needed for benefit, and it can carry fear. [12] Owning guide: mystical-type experience measures

Neuroplasticity

The brain's ability to change its connections. [23] Technical note: A meta-analysis of 29 human studies found no evidence that psychoplastogens raise peripheral BDNF; animal findings may not transfer. [23] Owning guide: neuroplasticity claims

NMDA receptor

A glutamate-system receptor that ketamine and PCP block. [1][7] Technical note: Ibotenic acid also acts on NMDA receptors, in a different way. [1][7] Owning guide: mechanisms vs clinical outcomes

Noribogaine

The main product the body makes from ibogaine. [4] Technical note: It stays in the body for days after ibogaine has cleared. [4] Owning guide: iboga (Tabernanthe iboga)

Off-label

Using an approved medicine for a purpose the regulator has not approved. [16] Technical note: Ketamine for depression is off-label; esketamine for treatment-resistant depression is on-label. [16] Owning guide: clinical formulations vs nonmedical products

Open-label

A study in which people know which treatment they receive. [24] Technical note: Some trials are open-label with blinded raters, as in ESCAPE-TRD. [24] Owning guide: registered clinical trials

Peyote

A small cactus (Lophophora williamsii) containing mescaline. [25][26][1] Technical note: US federal rules list peyote separately from mescaline and include an exemption for bona fide religious ceremonies of the Native American Church. [25][26][1] Owning guide: peyote (Lophophora williamsii)

Phase 2 and phase 3 trials

Stages of drug testing; phase 2 looks at early effectiveness and dosing questions, phase 3 confirms results in larger groups. [22][27] Technical note: Examples here: a phase 2 psilocybin trial and a phase 3 MDMA trial. [22][27] Owning guide: psychedelic clinical trials and research limits

Placebo effect

Improvement that comes from expecting to improve rather than from the drug. [12] Technical note: NIDA says it is hard to find a placebo that mimics a psychedelic's distinctive effects. [12] Owning guide: context and expectancy in psychedelic research

Polysubstance exposure

Taking more than one substance at the same time. [28] Technical note: Poison-center data link it to higher hospital admission for mushroom edibles. [28] Owning guide: combining psychoactive substances

Prodrug

A substance the body converts into its active form. [29] Technical note: Psilocybin is a prodrug converted to psilocin. [29] Owning guide: psilocybin vs psilocin

Psilocin

The active substance the body makes from psilocybin. [30][31] Technical note: It is also found in some products. [30][31] Owning guide: psilocin: compound guide

Psilocybe

A genus of fungi in which psilocybin and psilocin typically occur. [32] Technical note: Species names and common names do not reliably predict content. [32] Owning guide: Psilocybe species directory

Psilocybin

A compound found in some fungi that the body converts to psilocin. [30][29] Technical note: Classified as a classic psychedelic acting at 5-HT2A receptors. [30][29] Owning guide: psilocybin: compound guide

Psychedelic-assisted therapy

Giving a psychedelic or dissociative drug together with other treatment, mainly talk therapy. [12] Technical note: Only esketamine is FDA approved for therapeutic use among these drugs, according to NIDA. [12] Owning guide: what is psychedelic-assisted therapy

Psychoactive

Able to change mood, thoughts or perception. [1] Technical note: The word covers many unrelated substances with different actions. [1] Owning guide: what does psychoactive mean

Psychosis

Losing touch with reality. [12] Technical note: NIDA reports some evidence that psychedelics may trigger schizophrenia-like illness in people with predisposing factors; trials exclude people with psychosis or bipolar disorder. [12] Owning guide: psychosis vulnerability

PTSD

Post-traumatic stress disorder, with distressing memories, avoidance, hyperarousal and mood changes. [33] Technical note: MDMA-assisted therapy is investigational and not approved. [33] Owning guide: PTSD research

QT prolongation

A delay in the heart's electrical recovery that can lead to dangerous rhythms. [4][33] Technical note: Linked to ibogaine; also a safety assessment FDA reviewers noted as missing in MDMA trials. [4][33] Owning guide: iboga and ibogaine

Racemic

Containing equal parts of two mirror-image forms of a molecule. [8] Technical note: Ketamine is racemic; esketamine is one of its forms. [8] Owning guide: ketamine vs esketamine

REMS

Risk Evaluation and Mitigation Strategy, an FDA safety program that restricts how a medicine is given. [8] Technical note: Spravato is available only through a REMS. [8] Owning guide: clinical monitoring

Schedule I and Schedule III

US federal drug lists. Schedule I includes MDMA, LSD, psilocybin, mescaline and ibogaine; Schedule III includes ketamine. [25][34] Technical note: Read in 21 CFR 1308 on 2026-10-22. Laws change and this is not legal advice; scheduling is not a measure of safety. [25][34] Owning guide: controlled-substance status

Sclerotia (truffles)

Hardened underground masses of certain Psilocybe fungi, called magic truffles. [32] Technical note: They are not the same as the above-ground fruiting body. [32] Owning guide: psilocybin truffles

Semisynthetic

Made in a laboratory from a natural starting material. [21] Technical note: LSD is described this way. [21] Owning guide: natural vs synthetic compounds

Serotonin syndrome

A potentially life-threatening reaction from too much serotonin activity, often when serotonergic drugs are combined. [35] Technical note: Features include neuromuscular excitation, autonomic changes and altered mental status. [35] Owning guide: serotonergic medicines and substance-specific evidence

Set and setting

The person's mindset (set) and the surrounding people and place (setting). [1] Technical note: NIDA says both shape the response to a psychedelic. [1] Owning guide: clinical research vs recreational use

Treatment-resistant depression

Depression that has not responded to two or more consecutive treatments in the current episode. [24][8] Technical note: Esketamine is FDA-approved for it in adults. [24][8] Owning guide: treatment-resistant depression

Tryptamine

A chemical family structurally similar to serotonin that includes psilocybin and psilocin. [32] Technical note: DMT is also a tryptamine. [32] Owning guide: DMT vs 5-MeO-DMT

Valvulopathy

Heart-valve damage. [36] Technical note: Reviewers raise concern that repeated use of 5-HT2B-active drugs could cause cardiac fibrosis; this is unproven for microdosing. [36] Owning guide: long-term safety uncertainty in microdosing