Nine of twelve veterans with severe, treatment-resistant PTSD no longer met diagnostic criteria one month after two doses of psilocybin, according to an open-label pilot trial published Thursday in Communications Medicine.
This trial recruited at Ohio State University’s Center for Psychedelic Drug Research and Education from January 2023 to April 2025, with primary outcome assessments finished by that July. Participants were U.S. military veterans aged 21 to 64, all with severe PTSD (a CAPS-5 score of 35 or higher) that had persisted through at least three months on an SSRI or SNRI and at least six months of psychotherapy. Each received about eight hours of preparatory therapy across four weekly sessions, two dosing sessions of synthetic psilocybin spaced two to three weeks apart at 15 mg and then 25 mg, and about eight hours of integration therapy afterward. Stacey Armstrong is first author. She and Alan Davis are co-corresponding authors. The authors describe it as the first trial of psilocybin-assisted therapy in veterans with severe, treatment-resistant PTSD.
The numbers
Clinician-rated severity fell 27.5 points on average, from 39.7 at baseline to 12.2 at one month (p < 0.001, Cohen’s d = 2.30). Nine participants met the study’s thresholds for both response (a reduction of at least 50%) and remission (a score of 20 or below). Ten cleared the 15-point mark for clinically meaningful improvement. Self-reported PCL-5 scores fell from 56.6 to 16.2, most of that within a week of the second dose.
FDA wanted a safety trial, since no one had run psilocybin in veterans before. That is what this study was designed as. The PTSD numbers are secondary outcomes. No serious adverse events occurred. Headache was the most common complaint, with ten reports after the first dosing session and eight after the second, followed by anxiety and dizziness. All study-related events were mild to moderate and resolved on their own or without medical intervention. Heart rate peaked at 121 bpm across all sessions, and the highest systolic and diastolic readings recorded were 166 and 103 mmHg, inside the study’s limits.
Suicidal ideation did not increase at the group level. Two participants reported ideation within the past month at baseline, and ten reported it at some point in their lives. At one month after the second dose, three reported ideation, all of it passive.
Before anyone took a capsule
The team measured symptoms twice before dosing: at baseline, and again after the four preparation sessions. Severity had already fallen 6.3 points by that second reading. More telling, the size of that pre-dosing drop predicted where participants landed at one month (β = 0.487, p = 0.031). Expectancy, measured by a single question about how well participants thought the treatment would work, did not.
Davis told Psychedelics Today the result was no surprise. “Eight hours with a trauma specialist in the context of a psilocybin trial was in and of itself helpful,” he said, noting that he and Armstrong were both trained in trauma work before moving into psychedelic research. The team places psilocybin here as a catalyst inside a therapeutic context that was already producing measurable change on its own.
The design followed that logic. Earlier psilocybin trials have typically run one or two long preparation sessions. This team split preparation into two-hour weekly meetings across a month and opened at 15 mg so participants could practice grounding skills in a “moderate” session before the full dose (25 mg). They described the choice as trauma-informed, built for a population whose first obstacle is trust.
What it cannot show
Twelve people, no control group, no blinding, one month of follow-up. The paper concedes that small uncontrolled trials tend to produce larger effects than larger controlled ones, which is the right frame for a d of 2.30 (an effect size measure where 0.8 already counts as large, so expect this number to shrink once the design gets tighter). Screening excluded much of the population the treatment would eventually need to serve: a history of significant suicide attempt, bipolar or psychotic disorder, recent moderate or severe substance use disorder, or current antidepressant use all disqualified a candidate. Of 3,628 people who clicked the screening link, 52 reached an in-person screen and 12 finished.
The sample was 92% white. Asked about it, the researchers said psychedelic science needs to do better and that they needed to do better, tying the gap to funding thin enough that no one had staff time to build the trial as a community-integrated project in Columbus. The trial did enroll 25% women, more than double their share of the U.S. veteran population.
Funding came from the donors who backed the center’s launch with veterans as a stated interest. The trial ended at 12 participants instead of the planned 15, due to funding limits. At 12, preliminary analyses showed effects large enough that three more people would not have moved the result.
Armstrong, Davis, and co-author Rafaelle Lancelotta serve on the board of the Source Research Foundation, which Davis leads as president. The authors state the relationship did not influence the design, conduct, analysis, or reporting of the study.
Three-month and six-month data exist and are still being analyzed, so durability remains an open question. What this trial establishes is narrow: twelve veterans who had already cycled through first-line medication and psychotherapy improved sharply under conditions that required a research center, two facilitators in the room for every dosing session, and roughly 16 hours of therapy per person.
That is a level of care, and a treatment, not generally available to the American veteran population.
The paper appears to establish that it is safe to do more psilocybin research in this population. I’m excited to see it.
Questions about psilocybin for veterans with PTSD
What did the psilocybin trial in veterans with PTSD find?
Twelve U.S. military veterans with severe, treatment-resistant PTSD received two doses of psilocybin alongside about sixteen hours of therapy. Clinician-rated PTSD severity fell an average of 27.5 points from baseline to one month. Nine of the twelve met the study’s criteria for both treatment response and remission.
How many veterans took part in the study?
Thirteen enrolled and twelve completed the trial. The researchers had planned for fifteen and stopped early when funding ran out.
Is psilocybin an approved treatment for PTSD?
No. Psilocybin remains a Schedule I substance under federal law and is not approved by FDA for PTSD or any other condition. The psilocybin in this trial was administered under FDA-authorized research conditions at a university research center.
What are the study’s main limitations?
Twelve participants, no control group, no blinding, and one month of follow-up. All participants self-referred, screening excluded people with a history of significant suicide attempt or current antidepressant use, and 92% of the sample was white. Small uncontrolled trials also tend to produce larger effect sizes than larger controlled ones.
How does this compare to MDMA-assisted therapy for PTSD?
The paper notes its 75% remission rate is close to the 71% reported in a Phase 3 trial of MDMA-assisted therapy for PTSD. That trial was randomized and placebo-controlled with a far larger sample, so the two figures are not equivalent evidence.
Armstrong, S.B., Levin, A.W., Sepeda, N.D., Shaub, H., Hunter, T., Douglas, A., Lancelotta, R., & Davis, A.K. (2026). Safety, feasibility, and preliminary clinical outcomes of psilocybin-assisted therapy for veterans with severe, treatment-resistant PTSD: an open-label pilot clinical trial. Communications Medicine. https://doi.org/10.1038/s43856-026-01767-4
