Psychedelic Terms and Definitions

What does this word mean? Read our glossary of terms and definitions related to psychedelic science, medicine, and experience.
psychedelic terms and definitions
Author: Psychedelic Support
By Psychedelic Support
October 25, 2022

There are many words and phrases associated with psychedelics. Here is our glossary of terms related to psychedelic science, medicine, and experiences. Further resources are provided throughout.

5-HT2A Receptor

This receptor in the brain is responsive to serotonin. This specific serotonin receptor subtype of is thought to play a pivotal role in engendering the psychedelic experience, as it is the target of serotonergic or ‘classic’ psychedelics such as LSD and psilocybin. You may see these psychedelics described as 5-HT2A agonists, which means they bind to the receptor, generating a biological response. As such, 5-HT2A receptors are of great interest to psychedelic researchers in particular.

5-MeO-DMT (5-methoxy-N,N-dimethyltryptamine)

This psychedelic substance is found in the secretions of the Sonoran Desert Toad, and a number of plant species. The psychedelic experience precipitated by ingestion of 5-MeO-DMT is brief in comparison to other psychedelics, often lasting for just 20 minutes, for example. Take our course to learn more.

Active Placebo

Active placebos are designed to confuse a study participant as to whether they received the psychoactive drug under investigation or the comparator placebo drug. Niacin is a popular choice among psychedelic researchers, as it produces a tingling sensation. Active placebos are particularly useful in trials and studies involving the use of psychedelics, as otherwise the very existence of psychoactive effects would likely compromise the blinding of the trial.


After the primary effects of a psychedelic substance have subsided, individuals often report continued positive physical and mental effects. Walter Pahnke described this state as a period of ‘elevated and energetic mood with a relative freedom from concerns of the past and from guilt and anxiety.’ During the afterglow period, the effectiveness of psycho-therapeutic interventions is reported to be enhanced until the afterglow gradually subsides after two weeks to a month (see Majić et al., 2015 for discussion).


Ayahuasca is a brew made from a mixture of plants native to the Amazon basin, which is used by Indigenous peoples of South America as a sacrament. The brew typically contains Banisteriopsis caapi vine and the Psychotria viridis shrub, also known as chacruna. The former contains MAOIs, which orally activate the DMT in the other plant. A broad range of other plant species contain DMT, so there are variations in the exact mixture.

Breakthrough Therapy Designation

Designed to expedite the development and review of drugs intended to treat a serious condition, breakthrough therapy designations are awarded when preliminary clinical evidence indicates that the new therapy has the potential to provide substantial safety and efficacy improvements over available medications (FDA).

Center for Drug Evaluation and Research (CDER)

FDA Division tasked with ensuring “that safe and effective drugs are available to improve the health of people in the United States”. CDER’s remit covers all prescription, generic, and over-the-counter drugs – including fluoride toothpaste, sunscreen, etc. (FDA).

Center for Psychedelic Research, Imperial College London

A research center based at Imperial College of London that seeks to explore the use of psychedelics in mental health care, and to harness psychedelics “as tools to probe the brain’s basis of consciousness.” 


Changa is a mixture of plants, one of which contains DMT (N,N-Dimethyltryptamine). The dried plants, one of which is an MAOI, are combined with the crystalline form of DMT to create a smokable form of DMT that is more subtle in effect than vaporizing pure DMT.

Cluster Headaches

Short, but incredibly painful headaches that can occur on a daily basis for weeks, or even months, at a time. Unlike a typical headache, cluster headaches are concentrated on one side of the head and are often accompanied by other symptoms including, but not limited to, irritated eyes, runny nose, and facial sweating. Psychedelics, including psilocybin and LSD, are being examined as possible treatments (see, for example, Andersson et al., 2017; see also Cluster Busters, a nonprofit supporting research for better treatment for cluster headaches, including psychedelics).

Controlled Substances Act (CSA)

A statute, signed into law in 1970 by Nixon, establishing federal U.S. drug policy regulating certain substances according to five schedules (or classifications). Each schedule carries associated restrictions and penalties, with Schedule I being the most restricted. LSD, psilocybin, psilocin, mescaline, peyote, MDMA, cannabis, and DMT are all currently Schedule I drugs, designated as ‘drugs with no currently accepted medical use and a high potential for abuse.’

Default Mode Network (DMN)

The brain network that is most active when in a state of wakeful rest: daydreaming, for example. The network is also active when an individual is engaging in self-reflection, thinking about the past, planning for the future, etc. (see Andrews-Hanna, 2011). Research has linked both a hyperactive and less active DMN to mental health conditions.

Some psychedelics, including psilocybin, have a significant effect on the DMN. Research by Lebedev et al. (2015) suggests that the consumption of psilocybin causes a rapid dissolution of the connections that characterize the DMN. This has been associated with the common experience of ego-dissolution when using psychedelics.

Digital Therapeutics (DTx)

A broad category encompassing treatments or therapies that employ digital health technologies to improve health outcomes. According to the Digital Therapeutics Alliance: “Digital therapeutics deliver evidence-based therapeutic interventions to patients that are driven by high quality software programs to prevent, manage, or treat a broad spectrum of physical, mental, and behavioral conditions.” 

Dissociative Anesthetics

Dissociative anesthetics are a class of drugs that produce notable effects such as depersonalization (separation of the self from the body), derealization (belief that the natural world is not real), hallucinations and sensory deprivation. NMDA receptor antagonists, such as ketamine and PCP, induce dissociative anesthesia. While these drugs have been preferentially used as general anaesthetics, they are now widely used for their antidepressant properties in the treatment of suicidal thinking and major depressive disorder (MDD). Learn more in our ketamine course.

DMT (N,N-Dimethyltryptamine)

A psychedelic compound found in many plants and animals, and the primary ingredient in ayahuasca brews. When DMT is smoked, the trip is considerably shorter than that of other psychedelics, often lasting just 15 minutes (see Kaplan et al., 1974). While short, the effects are often intense (see Carbonaro and Gatch, 2016). When ingested orally through an ayahuasca preparation, the duration of effects is much longer. 


Dopamine is a neurotransmitter released by specific neurons that has widespread regulatory function in the brain. The molecule contributes to movement, learning, reward valence, motivation, mood states, and predicting internal states.

While dopamine is most attributed to pleasure by the media and public, the more nuanced pharmacological view is that it contributes to motivational salience – the neurotransmitter will modulate how an organism perceives predictors of an outcome (whether it was desirable or aversive) and thus, either propel it to further achieve or avoid the predictor that achieves the outcome. This theory of dopamine can be applied to drug-taking behavior, but also to other facets of learning.

Empathogens, entactogens

Psychoactive drugs that generate feelings of empathy or sympathy, such as feelings of oneness, emotional openness, bonding, and euphoria. MDMA is the drug most commonly associated with this class.


This term for psychedelics, coined in 1979 (Ruck et al., 1979), is generally reserved for their use in spiritual or sacred contexts. The word was coined in an attempt to rebrand psychedelics, and place it in its historical context as a ceremonial, spiritual tool.

Fast Track (FDA Designation)

“A process designed to facilitate the development, and expedite the review of drugs to treat serious medical conditions and fill an unmet medical need.” In order to fill an unmet medical need, one must provide a therapy where none exists, or provide a therapy that may be potentially better than available medications (FDA).


A subclass of psychoactive drugs that generally causes visual or auditory hallucinations. The term has fallen out of favor for describing psychedelic compounds but is still prevalent in medical literature and diagnostics. 


A naturally occurring psychoactive substance with dissociative properties found in plants such as Tabernanthe iboga. While it has historical roots in healing ceremonies and initiations in West Africa, the psychoactive plant is also used in efforts to overcome substance misuse and addiction via the temporary elimination of cravings and reduction of withdrawal symptoms.


A medical condition that makes a particular treatment or procedure advisable. Examples include major depressive disorder, treatment-resistant depression, cluster headaches, and PTSD.


Integration is the act of incorporating insights, challenging lessons, and new perspectives into your everyday existence. The word ‘integrate’ stems from Latin integrates, meaning to “to make whole; to complete; to restore, to renew,” – all describing the union of fractured parts and healing of past experiences. When higher states of consciousness emerge, especially from psychedelics, the period following is a ripe time to contemplate the experience’s meaning and take action to integrate it fully into one’s life.  

Investigational New Drug (IND)

A request for authorization from the Food and Drug Administration (FDA) to administer an investigational drug or biological product to humans (see FDA). This is the process through which companies obtain permission to initiate human clinical trials, and to facilitate interstate shipment of experimental drugs (e.g., to trial sites).


Ketamine is synthetic compound generally used as a dissociative anesthetic. Its fast-acting pain relief and short-term memory loss properties make it a popular anesthetic for medical procedures and injuries sustained in combat environments. More recently, lower doses of ketamine are being used to tackle treatment-resistant depression, with one of its enantiomers (esketamine) approved as a nasal spray for mental health conditions in the United States. Learn more in our ketamine course.

LSD (lysergic acid diethylamide)

A psychedelic compound first synthesized by Albert Hofmann in 1938. Hofmann accidentally ingested a small quantity of the drug while resynthesizing it five years after shelving it, and discovered its mind-altering properties. This marked the first intentional ingestion of LSD, with the day—April 19, 1943—now celebrated annually as Bicycle Day. LSD is colloquially known as acid.

LSD was used in psychotherapy during the 1950s and 1960s, but studies conducted at the time lacked rigor. More recently, MAPS completed a Phase 2 double-blind placebo-controlled study of LSD-assisted psychotherapy for anxiety (n=12), with positive results (Gasser et al., 2014). In 2020, MindMed launched Project Lucy, focused on LSD-assisted therapy for the treatment of anxiety disorders.

Magic Truffle

The psychoactive Sclerotia of psilocybin mushrooms. Sclerotia is a dense mass of hardened fungal mycelium which contains food reserves. They contain a lower dose of psilocybin than magic mushrooms, resulting in a short, yet impactful trip. Magic truffles may be purchased legally in the Netherlands.

Major Depressive Disorder (MDD)

Often referred to as ‘depression’. MDD is one of the most common mental health disorders in the United States, and across the world. Where pervasive low mood persists for at least two weeks, a diagnosis may be made. Affecting over 165 million people annually, MDD is onset by a combination of genetic, environmental, and physiological factors.

A particularly relevant clinical study examining the ability of psilocybin-assisted therapy to treat MDD was released in 2020 by the Center for Psychedelic and Consciousness Research at Johns Hopkins (Davis et al., 2020).


Monoamine oxidase inhibitors (MAOIs) change the levels of the brain chemicals norepinephrine, serotonin and dopamine called neurotransmitters which act to stabilize mood. MAOIs have been used to treat depression and are also a key ingredient in ayahuasca, the powerful psychedelic brew native to indigenous cultures in South and Central America.

MAPS (Multidisciplinary Association for Psychedelic Studies)

Founded by Rick Doblin in 1986, MAPS is a nonprofit seeking to raise awareness and understanding of psychedelics. MDMA has been the primary focus of MAPS Public Benefit Corporation in recent years, specifically in the treatment of PTSD. To this end, MAPS PBC received FDA approval to initiate Phase 3 trials in 2016, before the Agency went on to designate MDMA-assisted therapy as a breakthrough therapy for PTSD.

MDMA (3,4-methylenedioxymethamphetamine)

MDMA was first synthesized by pharmaceutical juggernaut Merck in 1912, but never came to market. Sixty years later, in the 1970s, Sasha Shulgin resynthesized it in his Bay Area home. This time, its empathogenic qualities were harnessed to augment psychotherapy, assisting in the building of trust between the therapist and the client. Despite the fact that the drug has been Schedule 1 in the United States since the late 1980s, MAPS has demonstrated its efficacy in the treatment of PTSD in phase 2 trials, landing MDMA-assisted therapy for PTSD a Breakthrough Therapy designation from the FDA. Take our MDMA course to learn more.


A naturally-occurring psychedelic, found in the peyote and San Pedro cactus (among other cactus species). Arthur Heffter first isolated and identified the compound in 1897, and it was first synthesized by Ernst Späth in 1918. Writer and philosopher Aldous Huxley recounted his experience with mescaline in The Doors of Perception (1954).


The ingestion of a sub-perceptual dose of a psychedelic (often psilocybin or LSD) with the aim of augmenting mental performance and/or mental health. There are two main protocols commonly used in microdosing: one, the Fadiman protocol, named after Dr. James Fadiman, has a one day on, two days off format, which then continues for four to eight weeks.

The second microdosing protocol is called the Stamets Stack, or the Stamet’s Protocol, named after fungi pioneer, Paul Stamets. This format follows four days on, three days off and repeats for four weeks, followed by two to four weeks of rest. This microdose protocol also recommends adding Lion’s Mane mushroom extract and niacin to aid in cognitive benefits and absorption/uptake of the beneficial compounds of the fungi. Take our psilocybin course to learn more.

Mystical Experience Questionnaire

A self-reported measure, in the form of a survey, used by researchers to understand whether a participant had a mystical experience (e.g., after ingesting psychedelics in a study). The conventional version, which has 43 items, was developed by Walter Pahnke and William Richards in the 1960s. A revised version, including 30 items, was validated in 2015 (Barrett et al., 2015) and is often used in contemporary research.


Neuroplasticity is the brain’s ability to adapt, modify, and change structure through the growth and reorganization of neural networks in the organ. Psychedelics such as LSD, DMT, ketamine, and psilocybin have been found to promote neuroplasticity in animal brains (Ly et al., 2018), one of the reasons why they may provide a novel means of treating mood and anxiety disorders. 

Observational Study

Observational studies or investigations are frequently used in the social sciences to understand relationships or associations in a target sample population where the independent variable is not under the control of the researcher. This method is typically employed when studying human psychology or behavior in a naturalistic environment, for example.

Open Label

Open label clinical trials are designed when both the researcher and the participant are aware of the treatment to be received (control/placebo or test drug in a two-arm clinical design). This type of trial design is converse to double blind studies in which neither the researcher nor the participant are aware of the treatment to be received. It is notable that regardless of the trial design, the type of treatment to be received can still be randomized.

Phase I (Clinical Trial)

Phase I clinical trials are intended to establish initial safety in humans. The drug is given to a small number of healthy volunteers to test for possible side effects and determine what the safe dosing range is.

Phase II (Clinical Trial)

Phase II clinical trials are the first in which the drug is tested in a small group of patient volunteers with the disease it is meant to treat. Phase II studies assess the safety and efficacy of the drug across a range of doses. Due to the small number of patients involved, conclusions about overall efficacy cannot be drawn, however Phase II trials provide guidance on how to optimally design larger Phase III trials to test the drug’s safety and efficacy.

Phase III (Clinical Trial)

Phase III trials, also known as pivotal trials, demonstrate a drug’s safety and efficacy in a large group of patients. Typically, at least two successful Phase III trials are required in order to provide sufficient evidence of efficacy. Given the large number of participants required, Phase III trials are most often multi-centre, international trials.

Phase IV (Clinical Trial)

Following the approval of a drug by the FDA, post marketing surveillance is conducted with the primary goal of monitoring long-term effects.


Compounds structured similar to dopamine that act as central nervous system stimulants, and have psychedelic effects. Well-known phenethylamines include mescaline and MDMA. Alexander Shulgin pioneered synthetic work in phenethylamines, documenting his efforts (which resulted in drugs such as 2C-B) in his book PiHKAL, which stands for Phenethylamines I Have Known And Loved. Take our MDMA course to learn more.


In a clinical trial with multiple treatment arms, it is necessary to test the drug efficacy against a control. The control group will typically receive a placebo, which could be, for example, an intravenous injection of saline or a sugar pill in place of the drug. Indeed, placebos serve as a comparison to the test drug to understand how symptoms change. See Active Placebo for more.

Post-Traumatic Stress Disorder (PTSD)

A mental disorder that may develop following exposure to a traumatic event. MAPS is working to achieve FDA approval for MDMA-assisted psychotherapy for PTSD.

Psilocin (4-HO-DMT)

The active metabolite of psilocybin (see below), which induces psychedelic experiences by activating receptors in the brain. Psilocybin is rapidly metabolized to psilocin, the chemical that reaches the brain.


A naturally-occurring psychedelic substance found in over 200 species of fungus. Psilocybin is a prodrug, which the body converts to psilocin. Take our psilocybin course to learn more. 

Psychedelic-Assisted Therapy (PAT)

Psychedelic-Assisted Therapy (PAT) is a therapeutic practice led by a registered clinician that employs traditional “talk therapy” (psychotherapy) while the patient is administered a psychedelic. It is thought that psychedelics can increase patient suggestibility and allow them to be more receptive to talk therapy, which can be reflected in everlasting changes in both attitudes and beliefs. PAT has been demonstrated to be effective for a range of mental health indications such as substance use disorder (SUD) and major depressive disorder (MDD).

Randomized Controlled Trial (RCT)

A randomized controlled trial is a type of clinical or basic science investigation that randomly assigns whether the participant is to receive a treatment or placebo/control. Therefore, it is thought that in a clinical setting the only observed differences between the two clinical arms must be attributed to the efficacy of the treatment intervention.


Salvia divinorum is a plant species that is a relative of sage which can be found growing in the wild in areas of Mexico. Mazatec shamans have used the leaves of the plant in healing rituals, and for medicinal purposes. The primary psychoactive in Salvia is salvinorin A, and ingestion of the plant results in a short, potent, psychedelic experience.


Serotonin is a neurotransmitter released by neuron terminals that has widespread regulatory function in the brain. The molecule contributes to reward, mood states, and numerous physiological processes. It is produced in the raphe nucleus of the brainstem. It is through the serotonin-binding receptor (5-HT2) that the hallucinogenic effects are produced with classic psychedelics LSD, mescaline, and psilocin.

Set and Setting

Refers to the participant’s mindset (‘set’) and physical and social environment (‘setting’) during a psychedelic experience. Supportive set and setting is thought to be central to a positive psychedelic experience.

SSRI (Selective Serotonin Reuptake Inhibitor)

A class of drugs that represent the most widely prescribed antidepressants in many societies. They are typically prescribed to individuals suffering major depressive disorder, anxiety disorders, and related mental health indications. Serotonin is a neurotransmitter, meaning it carries signals between nerve cells in the brain. Usually, when serotonin has carried a message, it is then reabsorbed by the nerve cells (reuptake). SSRIs, however, inhibit this reuptake, resulting in greater availability of serotonin in the brain.


A family of compounds with a similar structure to the neurotransmitter serotonin which includes psychedelics such as psilocybin, LSD, and DMT.

The content provided is for educational and informational purposes only and should be a substitute for medical or other professional advice. Articles are based on personal opinions, research, and experiences of the author(s) and do not necessarily reflect the official policy or position of Psychedelic Support.

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Author: Psychedelic Support
Psychedelic Support
Psychedelic Support offers evidence-based information to promote psychedelic education and safety. The content is developed by health professionals and researchers, and peer reviewed for accuracy by members of the Psychedelic Support Network and Allison Feduccia, PhD.

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