Psilocybin Glossary: Terms in Laws and Studies

5-HT2A receptor: A serotonin receptor found throughout the brain. Psilocin activates it, and in a classic 1998 study, blocking this receptor in volunteers blocked psilocybin's psychological effects.¹ More in what is psilocybin?
Aeruginascin: A minor tryptamine found in some psilocybin mushrooms. Whether it has psychoactive effects of its own hasn't been established.²
Baeocystin: A minor tryptamine and a building block in the mushroom's production of psilocybin. It may not be psychoactive itself.² Liberty caps tend to contain a lot of it.
Bluing: The blue color many psilocybin mushrooms turn where they're bruised or cut. It isn't a reliable identification test. See psilocybin mushroom species.
Breakthrough Therapy designation: An FDA status that speeds development of a drug for a serious condition when early evidence suggests a substantial improvement over existing treatments. Psilocybin programs from Compass Pathways and the Usona Institute hold it. See the research tracker.
Certificate of analysis (COA): A laboratory report showing what a specific batch contains, such as how much psilocybin and psilocin. Our guide to reading a lab report explains what a good one shows.
Cultivar or strain: A cultivated line within one species. Golden Teacher and Penis Envy are cultivars of Psilocybe cubensis, not separate species. See strains explained.
Decriminalization: Removing or reducing criminal penalties without creating a legal market. In the U.S., psilocybin decriminalization has mostly happened through city resolutions that make enforcement a low priority. See the legal status map.
Double-blind: A trial design in which neither participants nor the researchers assessing them know who got the real treatment. Psilocybin's strong effects make this hard to maintain. See the research tracker.
Entheogen: A psychoactive plant or fungus used in a spiritual or religious context. Many local measures use the term; Washington, D.C.'s Initiative 81, for example, covers "entheogenic plants and fungi." See the legal status map.
Facilitator: In Oregon, a state-licensed person who prepares a client for, supervises and follows up on a psilocybin session at a licensed service center. See Oregon.
Healing center: In Colorado, a state-licensed site where adults 21 and older can take psilocybin under supervision. See Colorado.
HPPD: Hallucinogen persisting perception disorder: visual disturbances that continue long after a hallucinogen has worn off. It's considered relatively rare.⁹ See safety.
Integration: The work, usually after a session, of making sense of a psychedelic experience and carrying anything useful into daily life. Oregon's program includes preparation, administration and integration stages. See Oregon.
Liberty cap: The common name for Psilocybe semilanceata, a small grassland mushroom and Europe's best-known psilocybin species. See liberty cap.
Lowest law enforcement priority: The mechanism most U.S. city psilocybin measures use: police and prosecutors are told to treat personal, non-commercial activity as their lowest priority. State and federal law still apply. See the legal status map.
MADRS: The Montgomery-Åsberg Depression Rating Scale, a 60-point clinician-rated scale. It's the main measure in most recent psilocybin depression trials. See the research tracker.
Microdose: An amount intended to be below the level that causes obvious psychedelic effects, usually taken repeatedly on a schedule. See what microdosing research shows.
Natural medicine: Colorado's legal term, from Proposition 122, for psilocybin, psilocin, DMT, ibogaine and mescaline (excluding peyote). Only psilocybin and psilocin are currently offered at healing centers. See Colorado.
Norbaeocystin: A minor tryptamine and an early building block in psilocybin production. Like baeocystin, it may not be psychoactive itself.²
Open-label: A study in which everyone knows what treatment they're getting. Results are useful but harder to separate from expectations.
Phase 1, 2 and 3: The stages of drug trials. Phase 1 tests safety in small groups, Phase 2 tests whether the drug works and at what dose, and Phase 3 confirms results in larger groups before a company applies for FDA approval. See the research tracker.
Placebo and active placebo: A placebo is an inactive comparison. An active placebo, such as niacin, causes some noticeable sensations to make it harder for participants to tell which group they're in.
Priority review voucher: An FDA voucher that speeds review of a drug application. The Commissioner's National Priority Voucher aims to cut the final review to one or two months. See Executive Order 14401.
Psilocin: The compound psilocybin is converted into in the body, and the one that produces the effects by acting on 5-HT2A receptors.³
Psilocybe: The genus that contains most known psilocybin mushrooms. See species.
Psilocybin: The main psychoactive compound in psilocybin mushrooms. It's a prodrug: the body converts it to psilocin.³ Schedule I under U.S. federal law. See what is psilocybin?
Schedule I: The most restrictive category under the federal Controlled Substances Act, for drugs considered to have a high potential for abuse and no currently accepted medical use. Psilocybin and psilocin have been in it since 1970. See the legal status map.
Service center: In Oregon, a state-licensed location where adults 21 and older can take psilocybin with a licensed facilitator. See Oregon.
Set and setting: "Set" is a person's mindset, including expectations and intentions; "setting" is the physical and social environment. Both strongly shape how a psychedelic experience goes.⁴ See safety.
Spiss fleinsopp: The Norwegian name for the liberty cap, used in Norway's narcotics regulation alongside Psilocybe semilanceata.⁵ See liberty cap.
Spore print: The color left when a mushroom cap drops its spores onto paper, used in identification. Psilocybe prints are dark purplish brown; those of the deadly Galerina are reddish brown.⁶ See the lookalike warning.
Teonanácatl: The Nahuatl word the Aztecs used for sacred mushrooms, usually translated as "god's flesh." See history.
Tolerance: A reduced effect after repeated use. Tolerance to psilocybin builds quickly and fades over about a week without use,⁷ and it carries over to LSD and vice versa.⁸
Treatment-resistant depression: Depression that hasn't improved after adequate trials of standard treatments, typically at least two. It's the condition in Compass Pathways' Phase 3 COMP360 trials. See the research tracker.
Trigger law: A state law that takes effect only if the FDA approves a psilocybin drug and it's federally rescheduled. It doesn't change the status of mushrooms. See the legal status map.

Sources

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Gotvaldová K et al. Extensive collection of psychotropic mushrooms with determination of their tryptamine alkaloids. International Journal of Molecular Sciences 2022;23(22):14068. doi:10.3390/ijms232214068. doi.org
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Hartogsohn I. Chapter on set and setting in harm reduction. Current Topics in Behavioral Neurosciences 2026;77:299-312. doi:10.1007/7854_2024_509. doi.org
Lovdata, Forskrift om narkotika (Norwegian narcotics regulation), FOR-2013-02-14-199. lovdata.no
UBC Beaty Biodiversity Museum, Galerina marginata. explore.beatymuseum.ubc.ca
Alcohol and Drug Foundation, "Psilocybin." adf.org.au
Isbell H et al. Cross tolerance between LSD and psilocybin. Psychopharmacologia 1961;2:147-159. doi:10.1007/BF00407974. doi.org
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