Summary: The first U.S. clinical trial of psilocybin-assisted therapy for military veterans with treatment‑resistant post‑traumatic stress disorder (PTSD) has shown a favorable safety profile and substantial clinical benefit. In an 11‑week open‑label pilot, intensive psychotherapy combined with two synthetic psilocybin dosing sessions produced high remission rates and large reductions in clinician‑rated PTSD symptoms.
Over the course of the 11‑week protocol, participants received 14–16 hours of structured psychotherapy (including eight hours of preparatory sessions and six to eight hours of post‑dosing integration) plus two supervised doses of synthetic psilocybin (15 mg then 25 mg). One month after the final psilocybin session, 75% of the 12 participants (nine veterans) no longer met diagnostic criteria for PTSD. On average, clinician‑rated symptom scores fell by 27.5 points from baseline to one month post‑treatment.
Key Facts
- High remission rate: 75% (9 of 12) of veterans with severe, treatment‑resistant PTSD were in remission at one month post‑treatment.
- Large symptom improvement: Mean clinician‑rated PTSD severity declined by 27.5 points from baseline to one month after treatment.
- Favorable safety profile: No serious adverse events occurred and suicidal ideation scores did not increase. The most common transient side effect was mild post‑dosing headache.
- Structured treatment model: The 11‑week protocol combined 8 hours of preparatory psychotherapy, two supervised psilocybin dosing sessions (15 mg then 25 mg), and 6–8 hours of integration therapy.
- Therapy and drug synergy: Preparation sessions produced measurable symptom reductions, and symptom decline accelerated substantially after psilocybin, supporting a model in which the drug acts as a catalyst for deep psychotherapeutic processing.
Source: Ohio State University
This open‑label pilot trial—the first U.S. study of psilocybin‑assisted therapy in veterans with severe, treatment‑resistant PTSD—evaluated safety, feasibility, and preliminary clinical outcomes. The study found no serious adverse events and no meaningful increases in suicidal ideation or behavior. Clinical improvements exceeded expectations for this difficult‑to‑treat population.
“For people with severe, treatment‑resistant PTSD, these results are striking,” said Stacey Armstrong, first author of the study. Many veterans do not respond to existing therapies, which leaves them at risk for chronic disability and elevated suicide risk; this unmet need motivated the research.
The protocol integrated psychotherapy and pharmacology: eight hours of preparatory psychotherapy, two psilocybin sessions spaced 2–3 weeks apart (15 mg then 25 mg of synthetic psilocybin), and six to eight hours of integration therapy. Across the group, clinician‑rated PTSD symptoms dropped substantially from baseline to the one‑month follow‑up. No severe adverse events were reported, and vital signs remained within safe limits during dosing sessions.
Investigators plan further analyses from this cohort, including durability of symptom improvements up to six months, biomarker studies, and assessment of treatment effects on sleep and substance use. The team also intends to pursue funding for a larger randomized, controlled trial to confirm these promising initial results.
Participant experience
To qualify, veterans had to have a DSM‑5 diagnosis of PTSD for at least six months, a Clinician‑Administered PTSD Scale for DSM‑5 (CAPS‑5) total score ≥35, and treatment‑resistant illness (prior counseling and medications had failed to produce meaningful relief). Recruitment demand was high: over 3,600 people completed the online prescreen, 668 were assessed for eligibility, 13 provided consent, and 12 completed the study (nine men and three women).
One participant, U.S. Army veteran Zachariah Collett, described decades of debilitating symptoms—nightmares, irritability, constant hypervigilance and strained relationships—that did not improve with prior therapies. After the combined regimen of integrative work and psilocybin sessions, he reported profound, lasting changes: improved calm, acceptance, forgiveness and better family relationships. He described the experience as gentle but powerful, providing the mental space to relearn healthy responses.
How the treatment appears to work
Study data suggest that psychotherapy alone led to some initial symptom relief, but the most substantial improvements followed psilocybin dosing. Investigators interpret this pattern as evidence that the medication can temporarily open an emotional window that allows deeper processing in therapy; the drug acts as a catalyst, and lasting change emerges through the therapeutic work and post‑treatment life changes.
Researchers acknowledge that open‑label pilot studies without control groups can produce larger effect sizes than randomized trials, so larger controlled studies are needed to confirm efficacy and generalizability.
“These treatments appear safe, are generally well tolerated, and show a strong signal of efficacy in this early study,” said senior author Alan Davis, director of the Center for Psychedelic Drug Research and Education. The research team is committed to conducting larger, methodologically rigorous trials to better define risks, mechanisms and long‑term benefits.
Funding: Supported by Ohio State’s College of Social Work, the Center for Psychedelic Drug Research and Education, the Clinical Research Center/Center for Clinical Research Management at The Ohio State University Wexner Medical Center, and Ohio State’s College of Medicine. Co‑authors from Ohio State include Adam Levin, Nathan Sepeda, Hillary Shaub, Taweh Hunter, Angela Douglas and Rafaelle Lancelotta.
Key Questions Answered:
A: Participants had severe, service‑connected PTSD that met criteria for treatment resistance—meaning prior evidence‑based psychotherapies and psychiatric medications had failed to provide meaningful relief.
A: Preparatory psychotherapy produced measurable symptom improvements, but symptom decline increased dramatically after psilocybin administration. The trial supports a model in which psilocybin serves as a pharmacological catalyst that facilitates deeper emotional processing during integration therapy.
A: The team will analyze longer‑term outcomes up to six months, examine biological markers and impacts on sleep and substance use, and seek funding for a larger randomized, double‑blind, placebo‑controlled clinical trial.
Editorial Notes:
- This article was edited by a Neuroscience News editor.
- The underlying journal paper was reviewed in full.
- Additional context was provided by the staff.
About this PTSD and psychopharmacology research news
Author: Emily Caldwell
Source: Ohio State University
Contact: Emily Caldwell, Ohio State University
Image: The image is credited to Neuroscience News
Original Research: “Safety, Feasibility, and Preliminary Clinical Outcomes of Psilocybin‑Assisted Therapy for Veterans with Treatment‑Resistant PTSD: A phase 2 non‑randomized clinical trial” by Stacey Armstrong et al., published in Communications Medicine. DOI: 10.1038/s43856-026-01767-4. Open access.
Abstract
Safety, Feasibility, and Preliminary Clinical Outcomes of Psilocybin‑Assisted Therapy for Veterans with Treatment‑Resistant PTSD: This phase 2, non‑randomized clinical trial tested an open‑label psilocybin‑assisted therapy protocol in U.S. military veterans with severe, treatment‑resistant PTSD.
Background
Psilocybin‑assisted therapy has shown promise for PTSD in civilian samples but had not been studied in U.S. veterans, who often have greater symptom severity and elevated suicide risk.
Methods
The pre‑registered pilot (ClinicalTrials.gov identifier NCT05554094) enrolled veterans aged 21–64 with PTSD ≥6 months and CAPS‑5 total severity ≥35. Twelve participants completed eight hours of preparatory therapy, two supervised dosing sessions (15 mg and 25 mg synthetic psilocybin) spaced 2–3 weeks apart, and approximately eight hours of integration therapy. Primary endpoints focused on safety and suicidal ideation/behavior; secondary endpoints assessed clinician‑ and self‑rated PTSD symptoms.
Results
From 668 individuals screened online, 13 consented and 12 completed the trial. No serious adverse events occurred. Non‑serious events included headache, anxiety and dizziness. Suicidal ideation did not increase. Clinician‑rated PTSD symptoms showed a large and statistically significant reduction (mean difference = 27.5 points; effect size d = 2.30; p < 0.001) from baseline to one month after treatment, with 75% of participants achieving remission. Early symptom improvements during preparatory therapy predicted later outcomes, while expectancy did not.
Conclusions
In this small open‑label trial, psilocybin‑assisted therapy was safe, feasible and associated with substantial short‑term clinical improvement in veterans with severe, treatment‑resistant PTSD. Larger randomized trials are needed to confirm efficacy, define mechanisms and establish long‑term outcomes.