RESEARCH · STUDIES LIBRARY
Psilocybin studies, in plain English.
63 published human studies of psilocybin, from the first modern brain studies to the latest depression trials. Each one has a short summary of what its abstract reports, including the limits its authors point out, with links to the paper.
These are research results, not treatment advice. Psilocybin is not an approved treatment in Canada. Most studies here gave psilocybin in a supervised research setting to screened volunteers; in two microdosing studies people took the doses themselves, and one is an interview survey. Many were small, and some found no clear benefit. Results from one study don’t say what would happen to anyone else. For the risks, see our safety page.
63 studies
18 randomised controlled trials
27 free to read in full
6 with Canadian researchers
Study details checked against Europe PMC on 26 October 2026. Source: Europe PMC, the free life-science literature database run by the European Bioinformatics Institute (EMBL-EBI).
All studies
Showing 63 of 63 studies
Psilocybin's effect on human brain synaptic plasticity
Johansen A et al. · Translational Psychiatry · 2026
What it found: PET scans of 15 healthy people found no significant overall rise in synapse density one week after a dose. People dosed in a therapy-like room, rather than inside an MRI scanner, had stronger experiences and larger increases.
- Participants
- 15
- Country
- Denmark
DOI 10.1038/s41398-026-04285-y · Europe PMC · Free full text
Psilocybin therapy for adult females with anorexia nervosa: pilot study
Douglass HM et al. · The British Journal of Psychiatry · 2026
What it found: 21 women with anorexia had three sessions alongside their usual treatment. Eating-disorder symptoms and motivation to change improved, but results varied widely; one participant made two suicide attempts 6–12 months later. Not randomised or placebo-controlled.
- Participants
- 21
- Country
- United Kingdom
Long-Term Efficacy of Psilocybin with Adjunct Psychotherapy in Treatment-Resistant Major Depression: 6- and 12-Month Naturalistic Follow-Up of a Phase 2b Trial
Mertens LJ et al. · Psychotherapy and Psychosomatics · 2026
What it found: 126 of the 144 people from the EPISODE trial came back for later checks. Depression scores were still clearly lower than at the start at 6 and 12 months, with no difference between the trial groups. People were free to start other treatments after week 12.
- Participants
- 126 (of 144 randomised)
- Country
- Germany
Efficacy and Safety of Psilocybin in Treatment-Resistant Major Depression: The EPISODE Randomized Clinical Trial
Mertens LJ et al. · JAMA Psychiatry · 2026
What it found: In 144 people with treatment-resistant depression, psilocybin did not beat an active placebo on the main measure (response at week 6: 17.0% vs 10.6%). Secondary measures suggested a meaningful effect, but there were safety signals, including one case of lasting visual changes (HPPD).
- Participants
- 144
- Country
- Germany
DOI 10.1001/jamapsychiatry.2026.0132 · Europe PMC · Free full text
A randomized clinical trial of repeated doses of psilocybin for the treatment of obsessive-compulsive disorder
Moreno FA et al. · Journal of Psychopharmacology · 2026
What it found: 15 people with OCD had weekly sessions of psilocybin or an active placebo (lorazepam). Psilocybin, but not placebo, lowered symptoms; after 8 weeks 73.3% met the response mark and 40% were in remission, fading but still substantial at 6 months. Very small.
- Participants
- 15
- Country
- United States
Psilocybin or Nicotine Patch for Smoking Cessation: A Pilot Randomized Clinical Trial
Johnson MW et al. · JAMA Network Open · 2026
What it found: 82 smokers had either one psilocybin session or a nicotine patch, both with 13 weeks of cognitive behavioural therapy. At 6 months, 40.5% of the psilocybin group versus 10.0% of the patch group were confirmed to have stayed off cigarettes. Nobody was blinded.
- Participants
- 82
- Country
- United States
DOI 10.1001/jamanetworkopen.2026.0972 · Europe PMC · Free full text
Comparing single- and repeat-dose psilocybin with active placebo for migraine prevention in an exploratory randomized controlled clinical trial
Schindler EAD et al. · Headache · 2026
What it found: 18 adults with migraine got zero, one or two psilocybin doses, with diphenhydramine as an active placebo. Migraine days fell by similar amounts in all groups, so the study couldn’t separate the drug’s effect from placebo.
- Participants
- 18
- Country
- United States
Investigating the safety and tolerability of single-dose psilocybin for post-traumatic stress disorder: A nonrandomized open-label clinical trial
McGowan NM et al. · Journal of Psychopharmacology · 2026
What it found: The first trial of psilocybin in PTSD: 22 adults had mostly short-lived side effects such as headache and nausea, with no serious ones. PTSD scores dropped meaningfully by week 4 and stayed down at week 12, but there was no control group.
- Participants
- 22
- Country
- United Kingdom
Psilocybin-assisted psychotherapy for depression and anxiety associated with life threatening illness: A phase 2b randomized controlled trial
Ross ML et al. · General Hospital Psychiatry · 2025
What it found: In 35 adults with a life-threatening illness, psilocybin with psychotherapy reduced depression and anxiety more than niacin placebo at 6–7 weeks, with benefits lasting to 26 weeks. There were more mild-to-moderate side effects, and one person withdrew because of anxiety.
- Participants
- 35
- Country
- Australia
Psilocybin in alcohol use disorder and comorbid depressive symptoms: Results from a feasibility randomized clinical trial
Luquiens A et al. · Addiction · 2025
What it found: In 30 recently detoxified patients with alcohol use disorder and depression, 55% of the psilocybin group were abstinent at 12 weeks, against 1 of 9 in the low-dose control group. A pilot focused on feasibility, and most patients correctly guessed their group.
- Participants
- 30
- Country
- France
Single-dose (10 mg) psilocybin reduces symptoms in adults with obsessive-compulsive disorder: A pharmacological challenge study
Pellegrini L et al. · Comprehensive Psychiatry · 2025
What it found: In 19 adults with OCD, symptoms (mainly compulsions) dropped more one week after a moderate dose than after a very low dose, but the effect faded over the next 3 weeks. Not randomised, and small.
- Participants
- 19
- Country
- United Kingdom
Psilocybin therapy for mood dysfunction in Parkinson's disease: an open-label pilot trial
Bradley ER et al. · Neuropsychopharmacology · 2025
What it found: 12 people with Parkinson’s disease and depression or anxiety had no serious adverse events and no worsening of Parkinson’s symptoms, and their mood improved for up to three months. The first data in a neurodegenerative disease; no control group.
- Participants
- 12
- Country
- United States
DOI 10.1038/s41386-025-02097-0 · Europe PMC · Free full text
Comparing Antidepressant Effects of Psilocybin-Assisted Psychotherapy in Individuals That Were Unmedicated at Initial Screening Versus Individuals Discontinuing Medications for Study Participation: Comparaison des effets antidépresseurs de la psychothérapie assistée par la psilocybine (PAP) chez les personnes non médicamentées à la sélection initiale et les personnes ayant arrêté les médicaments pour participer à l'étude
Chisamore N et al. · Canadian Journal of Psychiatry. Revue Canadienne de Psychiatrie · 2025
What it found: From a Toronto trial: people who had to stop their antidepressants to take part improved about as much as people who weren’t on antidepressants to begin with. Both groups had clinically significant benefits; an exploratory analysis.
- Participants
- 27
- Country
- Canada
Psilocybin-assisted therapy for relapse prevention in alcohol use disorder: a phase 2 randomized clinical trial
Rieser NM et al. · EClinicalMedicine · 2025
What it found: In 37 people who had just finished alcohol withdrawal treatment, one psilocybin session with brief therapy did not reduce relapse or drinking compared with placebo at 4 weeks or 6 months. The authors note the study was small.
- Participants
- 37 (analysed)
- Country
- Switzerland
DOI 10.1016/j.eclinm.2025.103149 · Europe PMC · Free full text
Single-dose psilocybin therapy for alcohol use disorder: Pharmacokinetics, feasibility, safety and efficacy in an open-label study
Jensen ME et al. · Journal of Psychopharmacology · 2025
What it found: 10 adults with severe alcohol use disorder drank less over the 12 weeks after one session: heavy drinking days fell by 37.5 percentage points. Blood levels of psilocin varied a lot from person to person, and there was no control group.
- Participants
- 10
- Country
- Denmark
Single-Dose Psilocybin for Depression With Severe Treatment Resistance: An Open-Label Trial
Aaronson ST et al. · The American Journal of Psychiatry · 2025
What it found: 12 people whose depression had not responded to at least five treatments had lower depression scores at weeks 3 and 12 after one session. The 5 who also had PTSD improved significantly less. Open-label, with no control group.
- Participants
- 12
- Country
- United States
Psilocybin Therapy for Clinicians With Symptoms of Depression From Frontline Care During the COVID-19 Pandemic: A Randomized Clinical Trial
Back AL et al. · JAMA Network Open · 2024
What it found: 30 US doctors, nurses and other clinicians with depression after frontline COVID-19 work: one psilocybin session lowered depression scores much more than niacin placebo at day 28. Burnout and PTSD scores leaned the same way but weren’t statistically significant or tested.
- Participants
- 30
- Country
- United States
DOI 10.1001/jamanetworkopen.2024.49026 · Europe PMC · Free full text
Single-dose psilocybin for U.S. military Veterans with severe treatment-resistant depression - A first-in-kind open-label pilot study
Ellis S et al. · Journal of Affective Disorders · 2025
What it found: In 15 US military veterans with severe treatment-resistant depression, 60% responded and 53% were in remission at week 3; at 12 weeks, 47% and 40%. Small, unblinded and without a control group.
- Participants
- 15
- Country
- United States
Low-dose psilocybin in short-lasting unilateral neuralgiform headache attacks: results from an open-label phase Ib ascending dose study
Rucker J et al. · Headache · 2024
What it found: Planned for six to 12 patients, the study stopped early after enrolling 4. Attacks fell by more than half in two people, but headache impact stayed severe, and the authors found no conclusive evidence for psilocybin in this condition.
- Participants
- 4 (enrolled; study stopped early)
- Country
- United Kingdom
Psilocybin desynchronizes the human brain
Siegel JS et al. · Nature · 2024
What it found: Repeated brain scans of healthy adults showed psilocybin massively disrupted normal brain-network patterns, more than three times as much as methylphenidate, most of all in the default mode network. A link between the hippocampus and that network stayed weaker for weeks.
- Participants
- Not stated in the abstract
- Country
- United States
DOI 10.1038/s41586-024-07624-5 · Europe PMC · Free full text
Single-Dose Synthetic Psilocybin With Psychotherapy for Treatment-Resistant Bipolar Type II Major Depressive Episodes: A Nonrandomized Open-Label Trial
Aaronson ST et al. · JAMA Psychiatry · 2024
What it found: In 15 people with bipolar II depression that hadn’t responded to treatment, depression scores fell sharply after one session and 12 met response and remission criteria at the end; mania and suicidality scores didn’t rise. Small and uncontrolled.
- Participants
- 15
- Country
- United States
DOI 10.1001/jamapsychiatry.2023.4685 · Europe PMC · Free full text
Psilocybin-assisted psychotherapy for treatment resistant depression: A randomized clinical trial evaluating repeated doses of psilocybin
Rosenblat JD et al. · Med · 2024
What it found: A Toronto trial in 30 people with hard-to-treat major or bipolar II depression, including some with suicidal thoughts. Those treated straight away improved more than those on the waiting list, and repeat sessions were linked to further improvement; there were no serious adverse events.
- Participants
- 30
- Country
- Canada
Psilocybin-assisted group therapy in patients with cancer diagnosed with a major depressive disorder
Agrawal M et al. · Cancer · 2024
What it found: 30 people with cancer and major depression had psilocybin together in small groups, each with their own therapist. Depression scores dropped markedly by week 8, with no serious drug-related events. There was no control group.
- Participants
- 30
- Country
- United States
Single-Dose Psilocybin Treatment for Major Depressive Disorder: A Randomized Clinical Trial
Raison CL et al. · JAMA · 2023
What it found: In 104 adults with major depression at 11 US sites, one psilocybin session with psychological support lowered depression scores more than niacin placebo, from day 8 through day 43. There were no serious treatment-related events, but more side effects overall with psilocybin.
- Participants
- 104
- Country
- United States
Psilocybin therapy for females with anorexia nervosa: a phase 1, open-label feasibility study
Peck SK et al. · Nature Medicine · 2023
What it found: A first safety study in 10 women with anorexia nervosa: one session with psychological support caused only mild, temporary side effects (two had low blood sugar without symptoms, resolved within 24 hours). It was not designed to show whether the treatment works.
- Participants
- 10
- Country
- United States
DOI 10.1038/s41591-023-02455-9 · Europe PMC · Free full text
Psilocybin for treatment resistant depression in patients taking a concomitant SSRI medication
Goodwin GM et al. · Neuropsychopharmacology · 2023
What it found: 19 people with treatment-resistant depression had psilocybin while staying on an SSRI antidepressant. Depression scores fell by week 3 and 8 (42.1%) were in remission, with no serious side effects. Open-label, with a short 3-week follow-up.
- Participants
- 19
- Country
- United Kingdom
DOI 10.1038/s41386-023-01648-7 · Europe PMC · Free full text
Pilot study of single-dose psilocybin for serotonin reuptake inhibitor-resistant body dysmorphic disorder
Schneier FR et al. · Journal of Psychiatric Research · 2023
What it found: In 12 adults with body dysmorphic disorder that hadn’t improved on an SSRI, symptoms dropped significantly over the 12 weeks after a single dose, and 7 (58%) were rated responders. Open-label, with no control group.
- Participants
- 12
- Country
- United States
Psilocybin-assisted therapy for major depressive disorder: An exploratory placebo-controlled, fixed-order trial
Sloshower J et al. · Journal of Psychopharmacology · 2023
What it found: Depression improved after both placebo (always given first) and psilocybin, with no significant difference between them, though effect sizes were larger after psilocybin. The authors say expectation and therapy effects make these studies hard to interpret.
- Participants
- 19 (placebo; 15 then had psilocybin)
- Country
- United States
Exploratory investigation of a patient-informed low-dose psilocybin pulse regimen in the suppression of cluster headache: Results from a randomized, double-blind, placebo-controlled trial
Schindler EAD et al. · Headache · 2022
What it found: A pulse of three low doses did not significantly reduce cluster headache attacks compared with placebo, though there was a hint of benefit in people with chronic cluster headache. Well tolerated; the authors note the study was very small.
- Participants
- 16 (randomised; 14 analysed)
- Country
- United States
Single-Dose Psilocybin for a Treatment-Resistant Episode of Major Depression
Goodwin GM et al. · The New England Journal of Medicine · 2022
What it found: In 233 people with treatment-resistant depression, a single high dose cut depression scores more than a very low control dose at 3 weeks; the middle dose did not. The benefit was not clearly sustained at 12 weeks, side effects were common, and suicidal thoughts or self-harm occurred in all groups.
- Participants
- 233 (three dose groups)
- Country
- United Kingdom
Percentage of Heavy Drinking Days Following Psilocybin-Assisted Psychotherapy vs Placebo in the Treatment of Adult Patients With Alcohol Use Disorder: A Randomized Clinical Trial
Bogenschutz MP et al. · JAMA Psychiatry · 2022
What it found: In 95 adults with alcohol use disorder, two psilocybin sessions with psychotherapy led to fewer heavy drinking days over 32 weeks than an active placebo (9.7% vs 23.6% of days). There were no serious adverse events among those who received psilocybin.
- Participants
- 95
- Country
- United States
DOI 10.1001/jamapsychiatry.2022.2096 · Europe PMC · Free full text
Microdosing with psilocybin mushrooms: a double-blind placebo-controlled study
Cavanna F et al. · Translational Psychiatry · 2022
What it found: Among 34 people starting to microdose psilocybin mushrooms, the active dose felt stronger than placebo only for those who correctly guessed what they had. There was no evidence of better well-being, creativity or thinking; the authors conclude expectation explains at least some reported benefits.
- Participants
- 34
- Country
- Argentina
DOI 10.1038/s41398-022-02039-0 · Europe PMC · Free full text
Increased global integration in the brain after psilocybin therapy for depression
Daws RE et al. · Nature Medicine · 2022
What it found: Brain scans from two depression trials showed that after psilocybin therapy, brain networks became more integrated with each other, and this tracked the improvement in depression. No such change was seen with escitalopram.
- Participants
- Not stated in the abstract
- Country
- United Kingdom
Direct comparison of the acute effects of lysergic acid diethylamide and psilocybin in a double-blind placebo-controlled study in healthy subjects
Holze F et al. · Neuropsychopharmacology · 2022
What it found: Compared head to head in 28 healthy people, the higher psilocybin dose produced effects much like both LSD doses but wore off sooner. Psilocybin raised blood pressure more, while LSD raised heart rate more.
- Participants
- 28
- Country
- Switzerland
DOI 10.1038/s41386-022-01297-2 · Europe PMC · Free full text
Efficacy and safety of psilocybin-assisted treatment for major depressive disorder: Prospective 12-month follow-up
Gukasyan N et al. · Journal of Psychopharmacology · 2022
What it found: The 24 people who completed treatment in a Johns Hopkins depression trial still had much lower depression scores 12 months later; 75% met the response mark and 58% were in remission. There was no control group at follow-up.
- Participants
- 24
- Country
- United States
Psilocybin microdosing does not affect emotion-related symptoms and processing: A preregistered field and lab-based study
Marschall J et al. · Journal of Psychopharmacology · 2022
What it found: In this preregistered, placebo-controlled study, three weeks of psilocybin microdosing did not change emotion processing or symptoms of anxiety and depression compared with placebo. Participants often guessed which they were taking.
- Participants
- Not stated in the abstract
- Country
- Netherlands
Effects of Psilocybin-Assisted Therapy on Major Depressive Disorder: A Randomized Clinical Trial
Davis AK et al. · JAMA Psychiatry · 2021
What it found: Adults with major depression who had two psilocybin sessions with psychotherapy had much lower depression scores than people still on the waiting list. The effects were large, but the comparison was a waiting list rather than a placebo.
- Participants
- 27 (randomised; 24 completed)
- Country
- United States
DOI 10.1001/jamapsychiatry.2020.3285 · Europe PMC · Free full text
Spontaneous and deliberate creative cognition during and after psilocybin exposure
Mason NL et al. · Translational Psychiatry · 2021
What it found: During the drug, volunteers reported more spontaneous creative insights but did worse on deliberate creativity tasks; seven days later they came up with more new ideas. Brain-network measures predicted these effects.
- Participants
- Not stated in the abstract
- Country
- Netherlands
DOI 10.1038/s41398-021-01335-5 · Europe PMC · Free full text
Trial of Psilocybin versus Escitalopram for Depression
Carhart-Harris R et al. · The New England Journal of Medicine · 2021
What it found: In 59 people with moderate-to-severe depression, psilocybin was not significantly better than the antidepressant escitalopram on the main measure at 6 weeks. Secondary measures leaned towards psilocybin, but those analyses weren’t corrected for multiple comparisons.
- Participants
- 59
- Country
- United Kingdom
Exploratory Controlled Study of the Migraine-Suppressing Effects of Psilocybin
Schindler EAD et al. · Neurotherapeutics · 2021
What it found: In 10 adults with migraine, weekly migraine days fell more in the 2 weeks after one psilocybin dose than after placebo, and the drop wasn’t linked to how intense the acute effects were. Exploratory and very small.
- Participants
- 10 (analysed)
- Country
- United States
Emotions and brain function are altered up to one month after a single high dose of psilocybin
Barrett FS et al. · Scientific Reports · 2020
What it found: A week after one high dose, 12 healthy volunteers had less negative mood and a lower amygdala response to faces. At one month, positive mood was still higher and trait anxiety lower, while the amygdala change had faded. A small, open-label pilot.
- Participants
- 12
- Country
- United States
DOI 10.1038/s41598-020-59282-y · Europe PMC · Free full text
Long-term follow-up of psilocybin-assisted psychotherapy for psychiatric and existential distress in patients with life-threatening cancer
Agin-Liebes GI et al. · Journal of Psychopharmacology · 2020
What it found: 15 participants from an earlier cancer trial were contacted about 3.2 and 4.5 years later. Lower anxiety, depression and death anxiety had largely held, with about 60–80% still meeting response criteria. The parent trial’s crossover design limits what this can show.
- Participants
- 15
- Country
- United States
Psychedelic effects of psilocybin correlate with serotonin 2A receptor occupancy and plasma psilocin levels
Madsen MK et al. · Neuropsychopharmacology · 2019
What it found: PET scans of 8 healthy volunteers showed psilocybin occupied up to 72% of the brain’s serotonin-2A receptors. The more receptors were occupied, and the more psilocin in the blood, the stronger the experience.
- Participants
- 8
- Country
- Denmark
Pharmacokinetics of Escalating Doses of Oral Psilocybin in Healthy Adults
Brown RT et al. · Clinical Pharmacokinetics · 2017
What it found: A study of how the body handles psilocybin in 12 healthy adults: it is converted to psilocin, whose half-life was about 3 hours, and very little leaves through the kidneys. No serious physical or psychological events occurred.
- Participants
- 12
- Country
- United States
Psilocybin with psychological support for treatment-resistant depression: six-month follow-up
Carhart-Harris RL et al. · Psychopharmacology · 2018
What it found: With the open-label study expanded to 20 patients, depression scores dropped sharply in the first 5 weeks and were still significantly lower at 6 months. The authors stress that limited conclusions can be drawn from an open-label trial.
- Participants
- 20
- Country
- United Kingdom
Psilocybin-occasioned mystical-type experience in combination with meditation and other spiritual practices produces enduring positive changes in psychological functioning and in trait measures of prosocial attitudes and behaviors
Griffiths RR et al. · Journal of Psychopharmacology · 2018
What it found: Healthy volunteers taking up meditation and spiritual practice were randomised, in three groups of 25, to high or very low doses. At 6 months, both high-dose groups showed large increases in measures such as gratitude, life meaning, forgiveness and closeness to others compared with the very-low-dose group.
- Participants
- Not stated in the abstract
- Country
- United States
Psilocybin produces substantial and sustained decreases in depression and anxiety in patients with life-threatening cancer: A randomized double-blind trial
Griffiths RR et al. · Journal of Psychopharmacology · 2016
What it found: In 51 people with life-threatening cancer and depression or anxiety, a high dose produced large drops in both compared with a very low dose. At 6 months, about 80% still showed clinically significant improvement.
- Participants
- 51
- Country
- United States
Rapid and sustained symptom reduction following psilocybin treatment for anxiety and depression in patients with life-threatening cancer: a randomized controlled trial
Ross S et al. · Journal of Psychopharmacology · 2016
What it found: Before the crossover, one psilocybin session with psychotherapy led to quick, large drops in anxiety and depression compared with niacin (a vitamin used as an active placebo). At the 6.5-month follow-up, about 60–80% still had clinically significant improvement.
- Participants
- 29
- Country
- United States
Long-term follow-up of psilocybin-facilitated smoking cessation
Johnson MW et al. · The American Journal of Drug and Alcohol Abuse · 2017
What it found: At 12 months, 10 of the 15 smokers from the open-label pilot (67%) were confirmed abstinent; at a later follow-up (on average 30 months after the first session), 9 (60%) were. Still a small study without a comparison group.
- Participants
- 15
- Country
- United States
Psilocybin with psychological support for treatment-resistant depression: an open-label feasibility study
Carhart-Harris RL et al. · The Lancet. Psychiatry · 2016
What it found: In 12 people with treatment-resistant depression, two sessions with psychological support were well tolerated, and depression scores were much lower 1 week and 3 months later. There was no control group; side effects included brief anxiety, confusion, nausea and headache.
- Participants
- 12
- Country
- United Kingdom
Psilocybin-assisted treatment for alcohol dependence: a proof-of-concept study
Bogenschutz MP et al. · Journal of Psychopharmacology · 2015
What it found: In 10 people with alcohol dependence, drinking did not change in the first 4 weeks of therapy, but abstinence increased significantly after the psilocybin sessions and the gains largely held to 36 weeks. A small proof-of-concept study with no control group.
- Participants
- 10
- Country
- United States
Pilot study of the 5-HT2AR agonist psilocybin in the treatment of tobacco addiction
Johnson MW et al. · Journal of Psychopharmacology · 2014
What it found: 12 of 15 long-term smokers (80%) were confirmed not smoking 6 months after psilocybin sessions given within a structured quit-smoking program. There was no comparison group, so the study can’t show that psilocybin itself made the difference.
- Participants
- 15
- Country
- United States
Neural correlates of the psychedelic state as determined by fMRI studies with psilocybin
Carhart-Harris RL et al. · Proceedings of the National Academy of Sciences of the United States of America · 2012
What it found: Brain scans of two groups of 15 healthy volunteers after placebo and psilocybin found only decreases in activity and blood flow, strongest in the brain’s main ‘hub’ regions, and a weaker link between two parts of the default mode network. The bigger the drop in one frontal area, the stronger the experience.
- Participants
- Not stated in the abstract
- Country
- United Kingdom
Psilocybin dose-dependently causes delayed, transient headaches in healthy volunteers
Johnson MW et al. · Drug and Alcohol Dependence · 2012
What it found: Psilocybin often caused a delayed headache in 18 healthy volunteers, more often and more strongly at higher doses. Every headache was temporary, lasting no more than a day, and none was severe or disabling.
- Participants
- 18
- Country
- United States
Psilocybin occasioned mystical-type experiences: immediate and persisting dose-related effects
Griffiths RR et al. · Psychopharmacology · 2011
What it found: Each volunteer had placebo and four doses. Effects grew with dose: at the two highest doses, 72% had a mystical-type experience and 39% had extreme anxiety or fear. The positive changes volunteers reported were still there at 14 months.
- Participants
- 18
- Country
- United States
Acute, subacute and long-term subjective effects of psilocybin in healthy humans: a pooled analysis of experimental studies
Studerus E et al. · Journal of Psychopharmacology · 2011
What it found: Pooling eight placebo-controlled studies of 110 healthy volunteers, most described the experience as pleasurable and enriching. Strong anxiety or dysphoria happened only at the two highest doses, in a small share of people, and was managed with support alone; follow-ups found no lasting harm.
- Participants
- 110 (pooled from eight studies)
- Country
- Switzerland
Pilot study of psilocybin treatment for anxiety in patients with advanced-stage cancer
Grob CS et al. · Archives of General Psychiatry · 2011
What it found: In 12 adults with advanced cancer and anxiety, psilocybin was given safely, with no clinically significant adverse events. Anxiety scores were lower at 1 and 3 months and mood was better at 6 months. A small pilot, and follow-up ratings were not blinded.
- Participants
- 12
- Country
- United States
Mystical-type experiences occasioned by psilocybin mediate the attribution of personal meaning and spiritual significance 14 months later
Griffiths R et al. · Journal of Psychopharmacology · 2008
What it found: At 14 months, 58% of volunteers rated their psilocybin session among the five most personally meaningful experiences of their lives and 67% among the five most spiritually significant; 64% said it had increased their well-being. These are self-ratings from a small, selected group.
- Participants
- 36 (volunteers)
- Country
- United States
Safety, tolerability, and efficacy of psilocybin in 9 patients with obsessive-compulsive disorder
Moreno FA et al. · The Journal of Clinical Psychiatry · 2006
What it found: All 9 people with OCD had marked short-term drops in symptoms during at least one session (23% to 100% lower scores), usually lasting past 24 hours, with no serious side effects. The study was very small, and the dose made no significant difference.
- Participants
- 9
- Country
- United States
Psilocybin can occasion mystical-type experiences having substantial and sustained personal meaning and spiritual significance
Griffiths RR et al. · Psychopharmacology · 2006
What it found: Compared with an active comparison drug (methylphenidate), psilocybin given in a supportive setting brought on experiences like spontaneous mystical experiences, along with anxiety for some. Two months later, volunteers rated the session as deeply meaningful, and community observers reported matching changes.
- Participants
- 30 (plus 6 in a blinding group)
- Country
- United States
Response of cluster headache to psilocybin and LSD
Sewell RA et al. · Neurology · 2006
What it found: Interviews with 53 people with cluster headache who had used psilocybin or LSD on their own. 22 of 26 psilocybin users said it stopped attacks, and many said it ended or delayed headache periods. These are self-reports from a self-selected group, not a trial.
- Participants
- 53
- Country
- United States
Acute psychological and physiological effects of psilocybin in healthy humans: a double-blind, placebo-controlled dose-effect study
Hasler F et al. · Psychopharmacology · 2004
What it found: Each of 8 healthy volunteers had placebo and four doses. Changes in perception, mood and attention grew with the dose, and attention-test scores fell by 50% at the two higher doses. Blood pressure rose briefly at the highest dose; heart rhythm and temperature did not change.
- Participants
- 8
- Country
- Switzerland
Psilocybin induces schizophrenia-like psychosis in humans via a serotonin-2 agonist action
Vollenweider FX et al. · Neuroreport · 1998
What it found: In healthy volunteers, psilocybin’s psychosis-like effects were blocked by drugs that block the serotonin-2A receptor (ketanserin, risperidone) but made stronger by haloperidol, which acts on dopamine. It was early human evidence that psilocybin works mainly through serotonin-2A receptors.
- Participants
- Not stated in the abstract
- Country
- Switzerland
How this library is made.
- Which studies. Human studies of psilocybin with published results: the studies our journal articles already cite, plus the most-cited psilocybin trials in Europe PMC and trials with Canadian authors. Reviews, study plans (protocols), animal and lab studies are left out. It is a selection of major studies, not every psilocybin paper ever published.
- The details. Title, authors, journal, year, DOI and the open-access flag come from each study’s Europe PMC record, fetched by its PubMed ID. “Free full text” links go to the open-access copy on Europe PMC; a paper without one may still be free on the publisher’s site.
- “What it found” is our plain-English summary of the study’s own abstract, and only the abstract. We checked that every number in it appears in that abstract. Abstracts leave things out, so open the paper for the full picture.
- Participants is the number the abstract gives (enrolled, randomised or analysed, as noted). Where an abstract doesn’t give one, we say so rather than work it out.
- Country is where the first author’s first listed institution is. Some trials ran in several countries.
- Canadian researchers means at least one author lists a Canadian institution in Europe PMC. It doesn’t always mean the study ran in Canada; for trials with Canadian sites, see the trial tracker.
How to read a study.
- Randomised controlled trial: people were assigned by chance to psilocybin or a comparison (placebo, another drug, a very low dose or a waiting list) and the groups were compared.
- Crossover trial: each person received both psilocybin and a comparison (placebo, another drug or several doses) at different sessions, so people were compared with themselves.
- Other controlled study: there was a comparison condition, but people were not randomised to it (for example placebo always came first).
- Open-label trial: everyone knew they were getting psilocybin and there was no comparison group, so the results can't separate the drug from expectation, therapy or time.
- Follow-up or secondary analysis: a later look at people from an earlier study, or a new analysis of data already collected.
- Survey or interviews: people described their own experiences; nothing was given as part of the study.
- Blinding is hard. Psilocybin’s effects are obvious, so people often guess whether they got it, which can colour their reports. Several studies here say so.
- Small numbers. 37 of the 63 studies report fewer than 30 participants in their abstract. Small studies can find effects that larger ones don’t.
Keep reading.
- How psilocybin works: from molecule to brain
- Psilocybin trials in Canada: live tracker
- The State of Psilocybin in Canada, 2026
- Psilocybin for depression: what the clinical trials found
- Psilocybin benefits: what clinical research has and hasn’t shown
- Johns Hopkins and the history of psilocybin research
- The Good Friday Experiment, 1962
We summarise what each abstract reports; we don’t rate or endorse any study. This page is educational and is not medical advice. Psilocybin is a controlled substance in Canada.