PSYCHEDELIC MEDICINE GLOSSARY
A shared language for a complex field.
Clear definitions for the research terms, substances and safety concepts that appear across psychedelic medicine reporting.
Definitions describe general usage; precise meanings may differ across studies, professions and jurisdictions.
Research terms
Safety concepts
Substances explained
No dosing guidance
How to use this glossary
Use these definitions as a starting point, then check how an individual paper or authority defines the term. A familiar label can hide important differences in study design, professional standards or legal context.
A–D
Foundations of research and safety
Adverse event
Any unfavourable medical occurrence during a study or treatment period. It does not automatically mean the intervention caused the event; researchers assess seriousness, timing and possible relationship separately.
Blinding
Keeping participants, researchers or assessors unaware of treatment assignment to reduce expectation and measurement bias. Psychedelic effects can be noticeable, which makes successful blinding unusually difficult.
Clinical significance
The practical or meaningful importance of a change in health or functioning. A statistically significant result is not necessarily large enough to matter clinically.
Clinical trial
A prospective research study involving people that evaluates an intervention under a defined protocol. Trials can examine safety, dosing ranges, biological effects or clinical outcomes.
Comparator or control group
A group used as a reference against which an intervention is assessed. It may receive placebo, standard care, another active treatment or a different study condition.
Contraindication
A condition, characteristic, medicine or circumstance that makes a particular intervention inadvisable or calls for additional caution because potential harms may outweigh benefits.
Dissociation
A broad term for experiences of detachment from thoughts, feelings, identity, memory, body or surroundings. It is not the same as a classic psychedelic effect, although experiences can overlap.
Double-blind study
A design in which both participants and relevant study staff are intended to remain unaware of treatment assignment. The exact people blinded should always be checked in the study protocol.
E–L
From efficacy to legal context
Effectiveness
How well an intervention works in ordinary practice, with the diversity, constraints and imperfect adherence found outside tightly controlled trials.
Efficacy
How well an intervention produces a desired outcome under specified and often carefully controlled research conditions.
Facilitator or guide
A non-standardised label for someone who supports a psychedelic experience. Training, regulation, clinical qualifications and legal status vary widely; the title alone does not establish competence.
Hallucinogen
A broad and imperfect umbrella term for substances that can substantially alter perception, mood or cognition. It includes several pharmacologically different groups and should not be treated as one uniform category.
Integration
A loosely defined process of reflecting on an experience and relating it to everyday life. Approaches vary, and the term does not by itself describe a validated or regulated treatment.
Investigational treatment
An intervention being studied that has not been established or authorised for the particular use being discussed. Participation in research is not the same as receiving routine clinical care.
Ketamine
A dissociative anaesthetic with established medical uses. Some ketamine-based treatments are used in specialist mental-health settings, but ketamine is pharmacologically distinct from classic psychedelics.
LSD
Lysergic acid diethylamide, a long-acting classic psychedelic that primarily affects serotonin 5-HT2A signalling. Research contexts and legal status differ from routine medical availability.
M–P
Common substances and study concepts
MDMA
3,4-methylenedioxymethamphetamine, a psychoactive substance with stimulant, prosocial and perception-altering effects. It is not a classic psychedelic and carries distinct physiological and psychological risks.
Microdosing
The repeated use of very small amounts of a psychedelic, usually intended to avoid a full psychedelic experience. Definitions vary, evidence remains limited and the term is not a standardised clinical protocol.
Mystical-type experience
A research construct used to measure experiences such as unity, sacredness, transcendence or ineffability. Associations with outcomes do not by themselves prove that the experience caused improvement.
Nocebo effect
Symptoms or negative experiences influenced partly by expectations, context or communication rather than only by the intervention’s direct pharmacological effects.
Open-label study
A study in which participants and researchers know which intervention is being given. This can be useful in early research but is more vulnerable to expectation and observer bias.
Phase 1, 2 and 3 trials
Broad stages of clinical development. Phase 1 usually emphasises safety and tolerability; Phase 2 explores preliminary efficacy and dose-related questions; Phase 3 aims to confirm benefit and monitor harms in larger populations.
Placebo
An inactive or comparison intervention designed to help separate specific treatment effects from expectations, natural change and study participation. Creating a convincing placebo can be especially difficult in psychedelic trials.
Psilocybin
A naturally occurring psychedelic compound found in certain fungi. The body converts it to psilocin, which acts mainly through serotonin receptors; clinical research uses controlled formulations and protocols.
Psychedelic
A broad term most often used for substances such as psilocybin, LSD, mescaline and DMT that produce marked changes in perception and consciousness, largely through serotonin 5-HT2A receptor activity.
Psychedelic-assisted therapy
A broad description of care combining a psychedelic drug session with psychological preparation, support or follow-up. The therapeutic model, professional roles and evidence base vary by substance and protocol.
R–Z
How to interpret findings
Randomisation
Assigning participants to study groups by chance. Proper randomisation helps balance known and unknown differences that could otherwise distort comparisons.
Risk of bias
The possibility that study design, conduct, analysis or reporting has systematically shifted results away from the truth. Common sources include unblinding, missing data, selective reporting and conflicts of interest.
Safety signal
Information suggesting a new or changing possible risk that deserves further investigation. A signal is a prompt to examine evidence, not automatic proof of causation.
Set and setting
Shorthand for the person’s mindset, expectations and circumstances (‘set’) and the physical, social and cultural environment (‘setting’). These factors may influence experience but do not remove pharmacological or medical risk.
Serious adverse event
A regulatory category for events such as death, life-threatening illness, hospital admission, significant disability or another medically important outcome. ‘Serious’ describes consequence, not necessarily whether the intervention caused it.
Statistical significance
A measure of how compatible data are with a specified statistical model, often expressed through a p-value or confidence interval. It does not establish clinical importance, certainty or lack of bias.
Treatment-resistant depression
A clinical label generally used when depression has not adequately improved after multiple appropriate treatments. Definitions differ across studies and health systems, so inclusion criteria should be checked.
Unblinding
When a participant, clinician or assessor correctly infers treatment assignment. In psychedelic trials, noticeable subjective effects can make this common and may amplify expectancy bias.
A term missing—or not clear enough?
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Educational information only. Definitions are not medical or legal advice and do not provide instructions for using controlled substances.
