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A Psychedelic Glossary

  • Active placebo: A type of placebo used in drug trials to fool the volunteer into thinking he has received the psychoactive drug being tested. In the psilocybin trials, researchers have used niacin, which produces a tingling sensation, and methylphenidate (Ritalin), which is a stimulant.

  • Ayahuasca: A psychedelic tea made from a combination of plants native to the Amazon basin, typically Banisteriopsis caapi and Psychotria viridis (or chacruna), and used sacramentally by indigenous peoples of South America. The chacruna plant contains the psychedelic compound DMT (N,N-dimethyltryptamine), but it is deactivated by digestive enzymes unless it is ingested with a monoamine oxidase inhibitor such as Banisteriopsis. In 2006, the U.S. Supreme Court affirmed the right of the Brazil-based UDV Church to use ayahuasca as a sacrament.

  • The Beckley Foundation: The organization established by Amanda Feilding in England in 1998 to support research into psychedelics and advocate internationally for the reform of drug laws. The organization is named for Feilding’s ancestral estate in Oxfordshire (

  • Council on Spiritual Practices (CSP): A nonprofit organization established by Bob Jesse in 1993 and “dedicated to making direct experience of the sacred more available to more people.” CSP helped organize and fund the first experiments in psychedelic research at Johns Hopkins; CSP also supported the suit that resulted in the 2006 Supreme Court decision recognizing ayahuasca as a sacrament in the UDV Church. In 1995, CSP developed and published the “Code of Ethics for Spiritual Guides” that many underground psychedelic guides have adopted (

  • Default mode network (DMN): A set of interacting brain structures first described in 2001 by the Washington University neuroscientist Marcus Raichle. The default mode network, called that because it is most active when the brain is in a resting state, links parts of the cerebral cortex with deeper and evolutionarily older structures of the brain involved in emotion and memory. (Its key structures include, and link, the posterior cingulate cortex, the medial prefrontal cortex, and the hippocampus.) Neuroimaging studies suggest that the DMN is involved in such higher-order “metacognitive” activities as self-reflection, mental projection, time travel, and theory of mind—the ability to attribute mental states to others. Activity in the DMN falls during the psychedelic experiences, and when it falls most precipitously volunteers often report a dissolution of their sense of self.

  • DMT (or N,N-Dimethyltryptamine): A rapid-onset, intense, and short-acting psychedelic compound sometimes referred to as “the businessman’s trip.” This tryptamine molecule is found in many plants and animals for reasons not well understood.

  • Empathogen: A psychoactive drug that produces a heightened sense of connectedness, emotional openness, and compassion. MDMA, or Ecstasy, is such a drug. Also sometimes called an entactogen.

  • Entheogen: From the Greek, “generating the divine within.” A psychoactive substance that produces or facilitates a spiritual experience. Entheogens have been used by many cultures for thousands of years, whether by shamans or as part of religious or spiritual practices. However, the term was not coined until the 1970s, by a group of scholars that included R. Gordon Wasson, Richard Evans Schultes, Jonathan Ott, and Carl Ruck. The word was intended to help rehabilitate psychedelics by distinguishing their ancient spiritual role from the recreational uses to which they were often put beginning in the 1960s.

  • Esalen, or the Esalen Institute: A retreat center in Big Sur, California, founded in 1962 to explore the various methods for expanding consciousness that often go under the umbrella of the human potential movement. Esalen was closely identified with the psychedelic movement before the drugs were banned; in the years afterward, a series of meetings took place at Esalen where strategies to rehabilitate and restart research into psychedelics were developed. Many psychedelic guides now working underground received their training at Esalen.

  • 5-HT2A receptor: One of several types of receptors in the brain that respond to the neurotransmitter serotonin. Psychedelic compounds also bind to this receptor, precipitating a cascade of (poorly understood) events that produce the psychedelic experience. Because of its distinctive molecular shape, LSD binds particularly well to the 5-HT2A receptor. In addition, a portion of the receptor folds over the LSD molecule and holds it inside the receptor, which might explain its intensity and long duration of action.

  • 5-MeO-DMT (5-methoxy-N,N-dimethyltryptamine): A powerful, short-acting psychedelic compound found in certain South American plants and in the venom of the Sonoran desert toad (Incilius alvarius). The toad venom is typically vaporized and smoked; 5-MeO-DMT obtained from plants is usually made into a snuff. The compound has been used sacramentally in South America for many years; it was first synthesized in 1936 and was not made illegal until 2011.

  • Hallucinogen: The class of psychoactive drugs that induce hallucinations, including the psychedelics, the dissociatives, and the deliriants. The term is often used as a synonym for psychedelics, even though psychedelics don’t necessarily produce full-fledged hallucinations.

  • Harvard Psilocybin Project: The psychological research program established by Timothy Leary and Richard Alpert (later Ram Dass) in the Department of Social Relations at Harvard in 1960. The researchers (who included Ralph Metzner, a graduate student) administered psilocybin to hundreds of volunteers “in a naturalistic setting”; they also conducted experiments with prisoners at Concord State Prison and with theology students at Boston University’s Marsh Chapel. Later, the group began working with LSD. The project was engulfed in controversy in 1962 and closed down after it had been reported that Alpert had given psilocybin to an undergraduate, in violation of its agreement with Harvard. Leary and Alpert established a successor organization in Cambridge but outside Harvard, called the International Federation for Internal Freedom.

  • Heffter Research Institute: A nonprofit established in 1993 by David E. Nichols, a chemist and pharmacologist at Purdue University, with several colleagues, to support scientific research into psychedelic compounds. The institute was named for Arthur Heffter, the German chemist, pharmacologist, and physician who first identified mescaline as the psychoactive component of the peyote cactus in the late 1890s. Established at a time when psychedelic research had been dormant for two decades, the Heffter Institute has played a pivotal, but quiet, role in the revival of that research, helping to fund most of the psilocybin trials done in America since the late 1990s, including the work at Hopkins and NYU (

  • Holotropic Breathwork: A breathing exercise developed in the mid 1970s by the psychedelic therapist Stanislav Grof, and his wife, Christina, after LSD was made illegal. By breathing rapidly and exhaling deeply, nearly to the point of hyperventilation, subjects enter an altered state of consciousness without the use of a drug. This trancelike state can give access to subconscious material. “Holotropic” means “moving toward wholeness.”

  • LSD (lysergic acid diethylamide): Also known as acid, this psychedelic compound was first synthesized in 1938 by Albert Hofmann, a Swiss chemist at Sandoz who was searching for a drug to stimulate circulation. LSD was the twenty-fifth molecule that Hofmann had derived from the alkaloids produced by ergot, a fungus that infects grain. Hofmann shelved the compound when it proved ineffective as a medicine, but five years later a premonition led him to resynthesize it. After accidentally ingesting a small quantity of LSD, he discovered its powerful psychoactive properties. In 1947, Sandoz began marketing LSD as a psychiatric drug under the name Delysid. It was withdrawn from circulation in 1966 after the drug appeared on the black market.

  • MAPS (Multidisciplinary Association for Psychedelic Studies): The nonprofit membership organization founded in 1986 by Rick Doblin to increase public understanding of psychedelics and support scientific research into their therapeutic applications. Based in Santa Cruz, California, MAPS has focused its efforts on MDMA, or Ecstasy, as a therapeutic intervention for people suffering from PTSD. In 2016, it won FDA approval to conduct phase 3 trials of MDMA in the treatment of PTSD; in 2017, the FDA designated MDMA as a “breakthrough therapy” for PTSD, clearing the way for an expedited review. Doblin, and MAPS, have played a central role in the revival of psychedelic research. MAPS also sponsors Psychedelic Science, the international conference on psychedelic research that takes place in Northern California every few years. (

  • MDMA (3,4-methylenedioxymethamphetamine): A psychoactive compound first synthesized by Merck in 1912 but never marketed. After the compound was resynthesized by the Bay Area chemist Alexander “Sasha” Shulgin in the 1970s, it became a popular adjunct to psychotherapy, because its “empathogenic” qualities helped patients form a strong bond of trust with their therapists. In the 1980s, the drug showed up in the rave scene, where it was sold under the name of Ecstasy (or E or later Molly); in 1986, the U.S. government put MDMA on schedule 1, declaring it a drug of abuse with no accepted medical use. However, recent drug trials sponsored by MAPS have demonstrated MDMA’s value in treating PTSD. MDMA is not considered a “classical psychedelic,” because it appears to operate on different brain pathways from LSD or psilocybin.

  • Mescaline: A psychedelic compound derived from several cacti, including peyote and San Pedro. The compound was first identified and named by the German chemist Arthur Heffter in 1897. The Doors of Perception is a first-person account of Aldous Huxley’s first mescaline experience.

  • Microdosing: The practice of ingesting a small, “subperceptual” dose of a psychedelic, usually LSD or psilocybin, every few days as an aid to mental health or mental performance. A common protocol is to take ten micrograms of LSD (a tenth of a medium dose) every fourth day. The practice is fairly new, and as yet the evidence for its effectiveness is anecdotal. Several trials are under way.

  • MK-Ultra: The code name for an undercover research program on psychedelic drugs conducted by the CIA beginning in 1953; it was closed down in 1963 or 1964. At various times, the CIA sought to determine whether LSD and related compounds could be used as a means of mind control; an interrogation tool (or truth serum); a biological weapon (added to a population’s water supply); or a political tool (by dosing adversaries to get them to do foolish things). As part of the research program, which at times involved forty-four universities and colleges, civilians and military personnel were dosed without their knowledge, sometimes with disastrous consequences. The public first learned about MK-Ultra during the Church Committee hearings on the CIA held in 1975; further hearings on the program were held in 1977. However, most of the agency’s documents on the program had been destroyed in 1973 on orders from director Richard Helms.

  • Mystical Experience Questionnaire: The psychological survey, developed by Walter Pahnke and William Richards in the 1960s, used to assess whether a volunteer in a trial of a psychedelic drug has undergone a mystical-type experience. It seeks to measure, on a scale of one to five, seven attributes of a mystical experience: internal unity; external unity; transcendence of time and space; ineffability and paradoxicality; a sense of sacredness; the noetic quality; and a deeply felt positive mood. Several revised versions of the MEQ have since been developed.

  • Noetic quality: A term introduced by William James, an American psychologist, to denote the fact that the mystical state registers not only as a feeling but as a state of knowledge. People emerge with the enduring conviction that important truths have been revealed to them. The noetic quality was, for James, one of the four marks of the mystical experience, along with ineffability, transiency, and passivity.

  • Phenethylamines: A class of organic molecule, and the name for one of the two principal types of psychedelic compounds; the other is the tryptamines. Mescaline and MDMA are examples of phenethylamines.

  • Psilocin: One of the two principal psychoactive compounds found in psilocybin mushrooms. The other is psilocybin, which breaks down to psilocin under certain conditions. Both compounds were isolated (from mushrooms provided by R. Gordon Wasson) and named by Albert Hofmann in 1958. Psilocin is what gives psilocybin mushrooms their bluish tint when bruised.

  • Psilocybe: A genus of approximately two hundred gilled mushrooms, roughly half of which produce psychoactive compounds such as psilocybin and psilocin. Psilocybes are distributed throughout the world. Their possession is illegal in most jurisdictions. The best-known members of the genus are Psilocybe cubensis, Psilocybe cyanescens, Psilocybe semilanceata, and Psilocybe azurescens.

  • Psilocybin: The main psychoactive compound found in psilocybin mushrooms and a shorthand for the class of mushrooms that contain it.

  • Psychedelic: From the Greek for “mind manifesting.” The term was coined in 1956 by Humphry Osmond to describe drugs like LSD and psilocybin that produce radical changes in consciousness.

  • Psycholytic: A term coined in the 1960s for a drug, or dose of a drug, that loosens constraints on the mind, allowing subconscious material to enter one’s awareness. Also the name for a form of psychotherapy that uses low doses of psychedelics to relax the patient’s ego without obliterating it.

  • Psychotomimetic: The name for a drug that produces effects resembling psychosis. This was a common term for LSD and drugs like it when they were first introduced to psychiatry in the 1950s; researchers believed they produced temporary psychoses that would yield insights into the nature of mental illness and give therapists the opportunity to experience madness firsthand.

  • Reducing valve: The term used by Aldous Huxley in The Doors of Perception for the mental filter that admits to our awareness only a “measly trickle of the kind of consciousness” we need to survive. In his view, the value of psychedelics was to open the reducing valve, giving us access to the fullness of experience and the universal “Mind at Large.”

  • Set and setting: The inner and outer environments in which a drug experience takes place; “set” is a term for the mind-set and expectations the person brings to the experience, and “setting” is the outward circumstances in which it takes place. Set and setting are particularly influential in the case of psychedelics. The terms are usually credited to Timothy Leary, but the concept was recognized and made use of by earlier researchers such as Al Hubbard.

  • Tryptamine: A class of organic molecule common in nature, and the name for one of the two principal types of psychedelic compounds; the other is the phenethylamines. LSD, psilocybin, and DMT are tryptamines. The neurotransmitter serotonin is also a tryptamine.

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