The following summaries draw from published, peer-reviewed clinical trials and registered case series. Where specific numerical outcomes are cited, they are taken directly from the primary publications listed. This page does not present anecdotal reports. All studies were conducted under institutional oversight and with full ethical review board approval. This content is for educational purposes only and does not constitute medical advice.
1. Johns Hopkins Cancer Anxiety Study (2016)
Full citation: Griffiths RR, Johnson MW, Carducci MA, et al. Psilocybin produces substantial and sustained decreases in depression and anxiety in patients with life-threatening cancer. Journal of Psychopharmacology. 2016;30(12):1181–1197.
This randomized, double-blind crossover trial enrolled 51 adults with cancer-related life-threatening diagnoses and significant depression or anxiety. Participants received either a high dose of psilocybin (22 or 30 mg/70 kg) or a very low dose (1 or 3 mg/70 kg, serving as an active control) in two sessions separated by five weeks, then crossed over.
At the six-month follow-up, approximately 80 percent of participants showed clinically significant decreases in both depressed mood and anxiety on standardized assessment scales (GRID-HAMD and STAI, respectively). Roughly 83 percent rated the experience as among the top five most personally meaningful of their lives, and 67 percent rated it as the single most meaningful experience. A parallel study by Ross et al. at NYU published in the same journal issue replicated these findings in a separate cohort.
The magnitude and durability of these effects were considered notable given the treatment-refractory nature of existential distress in terminal illness and the limited therapeutic window available to this population. These findings contributed substantially to the FDA granting Breakthrough Therapy Designation to psilocybin in 2018.
2. Johns Hopkins Major Depressive Disorder Study (2020)
Full citation: Davis AK, Barrett FS, May DG, et al. Effects of psilocybin-assisted therapy on major depressive disorder. JAMA Psychiatry. 2021;78(5):481–489.
This randomized clinical trial enrolled 24 adults with moderate-to-severe major depressive disorder (MDD) who had not responded adequately to antidepressants. Participants were randomized to immediate or delayed (eight-week waiting list) psilocybin treatment. Each participant received two psilocybin sessions (25 mg/70 kg) with trained facilitators, combined with psychotherapy preparation and integration sessions.
At the primary endpoint of four weeks after the second psilocybin session, the immediate treatment group showed a 71 percent response rate on the GRID-HAMD-17 scale and a 54 percent remission rate. The delayed control group showed 48 percent response and 28 percent remission after crossing over to receive treatment. Importantly, 58 percent of participants in the immediate group maintained a response at the one-month follow-up without any additional intervention. This was the first randomized controlled trial of psilocybin for MDD in the general population (not restricted to cancer patients), and it was published in one of the most rigorous peer-reviewed journals in psychiatry.
3. COMPASS Pathways Phase 2b Trial (COMP360, 2022)
Full citation: Goodwin GM, Aaronson ST, Alvarez O, et al. Single-dose psilocybin for a treatment-resistant episode of major depression. New England Journal of Medicine. 2022;387(18):1637–1648.
This was the largest randomized controlled trial of psilocybin to date at the time of its publication. The Phase 2b trial enrolled 233 adults with treatment-resistant depression (TRD, defined as failing at least two antidepressants) across 22 sites in ten countries. Participants were randomized to receive a single dose of synthetic psilocybin (COMP360) at 1 mg, 10 mg, or 25 mg under psychological support.
At three weeks after dosing, the 25 mg group showed a statistically significant reduction in MADRS depression scores compared with the 1 mg group (the reference arm). The 29 percent remission rate in the 25 mg group at week three was clinically meaningful in a population that had exhausted multiple prior treatment options. The 10 mg group did not separate from the control arm. Adverse events in the 25 mg group included headache, nausea, dizziness, and fatigue; one serious adverse event of suicidal ideation was reported and reviewed under the trial's safety monitoring board. This trial formed the basis for COMPASS Pathways' Phase 3 program.
4. Imperial College Psilocybin versus Escitalopram (2021)
Full citation: Carhart-Harris R, Giribaldi B, Watts R, et al. Trial of psilocybin versus escitalopram for depression. New England Journal of Medicine. 2021;384:1402–1411.
This randomized, double-blind trial at Imperial College London compared two sessions of psilocybin (25 mg, three weeks apart) against a six-week course of escitalopram (10–20 mg/day), the standard-of-care SSRI, in 59 patients with moderate-to-severe MDD. All participants also received psychological support sessions.
On the primary outcome measure (QIDS-SR-16 score at six weeks), the difference between groups was not statistically significant, suggesting psilocybin was not inferior to escitalopram on this measure. However, on ten of twelve secondary measures including well-being, meaning, emotional processing, and connectedness, psilocybin showed larger effect sizes. Depression response rates were 70 percent for psilocybin and 48 percent for escitalopram; remission rates were 57 percent and 28 percent respectively, though these differences did not reach significance due to the trial's sample size. The authors noted the trial was powered to detect a difference, not to demonstrate equivalence, and called for larger replication studies. This remains the most rigorous direct comparison of psilocybin against an active comparator.
5. Psilocybin for Tobacco Cessation (Johns Hopkins, 2014–2017)
Key citations: Johnson MW, Garcia-Romeu A, Cosimano MP, Griffiths RR. Pilot study of the 5-HT2AR agonist psilocybin in the treatment of tobacco addiction. Journal of Psychopharmacology. 2014;28(11):983–992. Follow-up: Garcia-Romeu A, Griffiths RR, Johnson MW. Am J Drug Alcohol Abuse. 2015.
This open-label pilot study at Johns Hopkins enrolled 15 adult smokers who had failed prior cessation attempts. Participants received two to three sessions of psilocybin (20–30 mg/70 kg) integrated into a cognitive-behavioral therapy framework for smoking cessation, with a target quit date set for the first dosing session.
Biochemically verified (urine cotinine and carbon monoxide breath test) smoking abstinence at 6 months was 80 percent. At 12-month follow-up, 67 percent remained abstinent. At a long-term follow-up averaging 30 months, 60 percent of participants who were contacted remained confirmed non-smokers. For context, varenicline (the best available pharmacotherapy for smoking cessation) typically produces 6-month abstinence rates of 25–35 percent in placebo-controlled trials. While the absence of a control group limits causal inference, these figures are substantially higher than standard-of-care outcomes and have prompted a fully randomized controlled trial.
6. Psilocybin for Alcohol Use Disorder (Bogenschutz et al., 2015–2022)
Key citations: Bogenschutz MP, Forcehimes AA, Pommy JA, et al. Psilocybin-assisted treatment for alcohol dependence. Journal of Psychopharmacology. 2015;29(3):289–299. Randomized trial: Bogenschutz MP, et al. JAMA Psychiatry. 2022;79(10):953–962.
The original proof-of-concept study enrolled 10 adults with alcohol use disorder. Following psilocybin sessions, the percentage of drinking days decreased from 32 percent in the month before the first session to 10 percent in the month following the second session. The improvements persisted through the 36-week observation period.
The subsequent randomized, double-blind, placebo-controlled trial (published in JAMA Psychiatry, 2022) enrolled 93 participants across multiple sites. The psilocybin group showed a significantly greater reduction in heavy drinking days compared with the diphenhydramine control (active placebo) group: the psilocybin group had 9.7 percent heavy drinking days at the end of the 32-week observation versus 23.6 percent in the control group, representing a large and statistically significant effect. This multi-site trial is considered the strongest evidence to date for psilocybin in addiction treatment and is frequently cited in policy discussions around Schedule I rescheduling.
7. Veterans and PTSD: Emerging Evidence
As of 2026, no completed, published, fully randomized controlled trials specifically targeting PTSD with psilocybin have been completed in veteran populations. However, several active trials are underway, and data from observational case series and compassionate use programs have informed ongoing research design.
The most relevant completed work includes studies at the Lundquist Institute and at University of California San Francisco examining psilocybin in trauma-related presentations. Published case series (Goldsmith et al., 2020, Journal of Psychiatric Practice) have documented clinically meaningful reductions in PTSD symptom severity following psilocybin-assisted therapy in small case groups, with participants showing decreases on the CAPS-5 (Clinician-Administered PTSD Scale) maintained at follow-up. MAPS' psilocybin-for-PTSD protocol builds on the structured therapeutic model developed for the MDMA-PTSD program, which itself completed Phase 3 trials by 2023.
Veteran-focused psilocybin programs including the Heroic Hearts Project facilitate access to international therapeutic programs and collect observational outcome data that feeds into academic publications. This data suggests convergent benefit, but the field awaits rigorous placebo-controlled confirmation in diagnosed PTSD specifically.
Important Caveats About These Findings
Several limitations apply to the body of evidence summarized above:
- Sample sizes are small. Most trials to date have enrolled fewer than 60 participants. Phase 3 replication trials with larger cohorts are needed before these findings can be considered definitive.
- Blinding is challenging. Psilocybin produces unmistakable subjective effects, making it difficult to blind participants or therapists to treatment assignment. This can inflate reported outcomes through expectancy bias.
- Therapist contact hours are high. Most protocols involve 8–15 hours of therapist contact per participant. It is difficult to separate the specific pharmacological contribution of psilocybin from the non-specific effects of intensive therapeutic attention.
- Participant selection effects. Trials typically exclude individuals with personal or family history of psychosis, bipolar I disorder, active suicidality, or certain cardiovascular conditions. Results may not generalize to these populations.
- Follow-up duration is limited. Most trials report outcomes at 4–26 weeks. Long-term durability beyond one to two years is not yet well characterized.
Understanding both the promise and the limitations of the existing evidence base is essential for anyone seeking to evaluate psilocybin research responsibly. For the primary source documents cited here, see the PDF Library page for direct links to open-access full texts.