For decades, standard PTSD treatments have failed a significant portion of veterans. A new clinical trial found that psilocybin therapy put 75% of treatment-resistant patients into full remission
Post-traumatic stress disorder affects millions of veterans worldwide, but the treatments available for it have always worked unevenly. Cognitive processing therapy, prolonged exposure therapy, and FDA-approved medications like sertraline and paroxetine help a substantial portion of patients. For another portion, they do not. That group, classified as treatment-resistant, has faced a decades-long gap between the severity of their condition and the options available to address it. Elevated rates of disability, dropout from care, substance use, and suicide cluster around this population with unusual density.
A new study published today in Communications Medicine, part of the Nature portfolio, reports the results of the first US clinical trial of psilocybin-assisted therapy designed specifically for military veterans with treatment-resistant PTSD. The trial was conducted at Ohio State University’s Center for Psychedelic Drug Research and Education. Twelve veterans completed the full protocol. One month after the trial concluded, nine of them, 75%, no longer met the diagnostic criteria for PTSD.
“For a population with severe treatment-resistant PTSD, these results are striking,” said Stacey Armstrong, the study’s first author and associate director of the Center for Psychedelic Drug Research and Education at Ohio State’s College of Social Work.
Who was in the trial and what they went through
To qualify for enrollment, participants had to have a DSM-5 diagnosis of PTSD for at least six months, a clinician-rated symptom severity score of 35 or above on the standard assessment scale, and a documented history of treatment resistance, meaning meaningful trials of established therapies had not provided relief.
The scale of interest was immediate. Over 3,600 veterans reached out after hearing about the study. Of those, 668 completed a formal prescreening. Thirteen ultimately enrolled, one withdrew before the first dosing session, and twelve completed the full protocol. Nine were men and three were women.
The 11-week treatment structure had three distinct phases. The first was preparation: eight hours of individual psychotherapy sessions designed to establish trust with the therapist, process expectations, and build the psychological groundwork for the dosing sessions. The second was the psilocybin administration itself, two sessions spaced two to three weeks apart, using 15 milligrams in the first session and 25 milligrams in the second. Each session lasted several hours and was conducted with a trained therapist present throughout. The third phase was integration: six to eight additional hours of therapy in the weeks following the doses, focused on processing what emerged during the sessions and translating it into lasting behavioral and emotional change.
From baseline to one month after the second psilocybin dose, the group showed an average reduction of 27.5 points on the clinician-administered PTSD assessment scale. That is a large effect size, measured statistically as d = 2.30, which is unusually high for any psychiatric intervention.
What made the remission rate possible
One of the more nuanced findings in the study concerns the question of where the therapeutic benefit actually comes from. In the psychedelic therapy field, the debate has persisted for years: is it the drug, the therapy, or the combination that drives outcomes? Proponents of different positions have argued for each.
This trial produced data that allows a partial answer. Clinician ratings of PTSD severity dropped measurably during the preparation therapy phase, before any psilocybin was administered. That indicates the structured psychotherapy component alone was doing something. But the reduction after the psilocybin sessions was dramatically larger, suggesting the drug was catalyzing a depth of processing that the therapy alone could not produce.
“This treatment is more than just a drug,” said Alan Davis, senior author of the study and director of the Center for Psychedelic Drug Research and Education. “The drug itself is a catalyst for the deep work that opens a window for people to perhaps access things they wouldn’t be able to access emotionally otherwise, and what that does is catalyze the therapeutic process after. That’s where the magic actually happens. It happens in the therapy, and in the changes that people start to make in their lives after the treatment’s concluded.”
The trial also tracked expectancy, the degree to which participants believed the treatment would work, as a potential driver of outcomes. Expectancy did not predict symptom change. The therapy engagement during the preparation phase did. This matters because it suggests the effect is not simply a placebo response driven by optimism or belief in psychedelics.
The safety picture
For a population carrying elevated suicide risk, the safety data in this trial is among the most clinically significant parts of the report. Suicidal ideation scores did not increase from baseline to one month post-treatment. No serious adverse events occurred during any phase of the trial. Heart rate and blood pressure remained within safe limits during the dosing sessions. The most commonly reported side effect was a mild headache following psilocybin administration.
This matters because the gap between clinical need and available treatment for veterans with PTSD is partly driven by concerns about safety. Standard medications carry their own adverse event profiles. Any novel intervention entering this population needs to demonstrate that it does not worsen the very outcomes it is trying to address.
“While treatments do work for some veterans with PTSD, they’re falling short for many, leaving veterans to continue to search for solutions, which can lead to treatment dropout, long-term disability and elevated suicide risk,” Armstrong said. “It’s this unmet need that inspires us.”
One veteran who participated in the trial, Zachariah Collett, served as a military police paratrooper in Iraq before being medically retired at 25 with PTSD among his diagnoses. He described years of nightmares, constant hypervigilance, and an anger that affected his family before finding the psilocybin protocol. Three years after completing the treatment, he described the change as profound. “It allowed me the opportunity to create peace, and stillness, and acceptance, and forgiveness and grace,” he said.
What the limitations mean for what comes next
The research team is explicit about what a pilot trial of 12 people can and cannot establish. Open-label studies without a control group consistently produce larger effect sizes than randomized controlled trials, because participants know they are receiving the active treatment, therapists know they are delivering it, and neither group is blind to the condition. The 75% remission figure may shrink in a larger, blinded, placebo-controlled trial.
The sample was also drawn entirely from veterans who self-selected into a psilocybin study, a group likely to hold more positive expectations about psychedelic therapy than the broader veteran population. And the follow-up endpoint was one month post-treatment. Whether the remission holds at six months, twelve months, or beyond is a question the current paper cannot answer, though the team has planned follow-up assessments up to six months.
That longer-term question is not academic. Earlier psilocybin trials for depression, including work by Davis himself, have documented remission that persisted for five years. If similar durability holds for PTSD, the implications for veteran mental health would be substantial, given that the current standard of care requires ongoing treatment to maintain benefit.
The team is currently seeking funding for a larger randomized controlled trial. What this pilot provides is the safety and preliminary efficacy data required to justify that next step.
“Recognizing the tools that we have don’t work so well and recognizing the significant burden of PTSD in the United States carried by our servicemen and women and veterans, this seemed like the right direction to go,” Armstrong said.
The study “Safety, Feasibility, and Preliminary Clinical Outcomes of Psilocybin-Assisted Therapy for Veterans with Treatment-Resistant PTSD: A phase 2 non-randomized clinical trial” was authored by Stacey Armstrong, Adam Levin, Nathan Sepeda, Hillary Shaub, Taweh Hunter, Angela Douglas, Rafaelle Lancelotta, and Alan Davis at The Ohio State University, and published July 30, 2026 in Communications Medicine.
Source: Ohio State University Center for Psychedelic Drug Research and Education. DOI: 10.1038/s43856-026-01767-4
