Psilocybin trial shows striking remission rates for veterans with PTSD

The first U.S. clinical trial of psilocybin-assisted therapy in veterans with PTSD who got no relief from conventional treatments has established that the protocol is safe, causing no serious adverse events or increases in suicidal thinking or behavior.

But the preliminary clinical results exceeded researchers' expectations: In the pilot trial with 12 veterans, 75% of participants were in remission one month after the study's end. Their symptoms no longer met the criteria for post-traumatic stress disorder.

"For a population with severe treatment-resistant PTSD, these results are striking," said Stacey Armstrong, first author of the new study, published today (July 30, 2026) in Communications Medicine.

"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," said Armstrong, senior researcher and associate director of the Center for Psychedelic Drug Research and Education (CPDRE) in The Ohio State University College of Social Work.

"It's this unmet need that inspires us."

The 11-week trial period combined eight hours of psychotherapy followed by two doses, 15 milligrams and 25 milligrams, of synthetic psilocybin, the active ingredient in magic mushrooms. Six to eight more hours of integrative therapy followed the drug treatment.

From baseline to one month after treatment was finished, there was an overall average drop of 27.5 points in clinician-rated PTSD symptoms among the group. Nine participants had a clinical response to treatment and were in remission. No severe adverse events occurred, with the most common side effect being a mild headache after taking psilocybin. Suicidal ideation scores did not significantly change from baseline to one month post-treatment.

Future papers from this study will assess the treatment's effectiveness up to six months after the trial, as well as biological changes and effects on other PTSD-related problems like sleep disorders and substance use, said Alan Davis, senior author of the study, director of the CPDRE and associate professor of social work at Ohio State.

Anecdotal observations, and previous research showing that depression remission endured for five years after an earlier psilocybin trial that Davis co-led, suggest the combined therapies could have staying power for many people whose symptoms are not eased by traditional therapies.

"It's been an incredible honor to work with veterans in this study, many of whom have been suffering with PTSD for decades or longer," said Davis, who also holds faculty appointments in psychology and internal medicine at Ohio State.

"Some experiences we've seen in actual treatment sessions are extremely profound and meaningful. The ability for them to go back and to revisit really difficult events that happened to them and to find a new way of understanding them and a new way of moving forward in their life has really been exciting."

One participant's experience

To be eligible for the trial, veterans had to have severe PTSD that was considered treatment-resistant. The need for help in this population became quite evident as participant recruitment began: Over 3,600 applicants reached out to partake in online prescreening and 668 were assessed for eligibility. Though the initial goal was 15 participants, the final number was 12 – nine men and three women.

Zachariah Collett, a U.S. Army veteran from Washington Court House, Ohio, considers himself one of the lucky ones who was selected to participate.

Collett joined the Army in 2002 as an enlisted soldier and later became a military police corps paratrooper, serving a 28-month combat tour in Iraq. By age 25 he was medically retired. Among the diagnoses and service-connected disabilities that led to retirement was post-traumatic stress disorder.

His symptoms included nightmares, a short temper, feeling constantly on guard and being angry virtually all the time – leading to behavior that had a negative effect on his family.

I was just absolutely tortured by the internal struggle, the internal dialogue, the noise inside my head and the inability even to just be still." 

Zachariah Collett, U.S. Army veteran from Washington Court House, Ohio

Years of trying counseling and medications didn't help.

It was an intensive 41-day self-discovery experience combining a healthful diet with a series of integrative therapies that first put Collett on the path to healing. When he later learned about the psilocybin trial, he saw it as the perfect opportunity – and medicine – to take a "deeper dive."

Now three years out from the treatment, he said the psilocybin-assisted therapy had a profound effect on him, his family and his marriage.

"For the first six months to a year, I felt like I had this fantastic set of training wheels while I'm relearning the way to act in situations," he said. "That's the great thing about this medicine. It's gentle and it allowed me the space to rediscover, or discover, things I didn't know I was capable of doing.

"It allowed me the opportunity to create peace, and stillness, and acceptance, and forgiveness and grace – all those things opposite of resentment and anger and hatred. It's rather beautiful."

Where the magic happens

A rigorous psychotherapy schedule is a key part of the process, with evidence from the trial suggesting that PTSD symptoms were lowered even before the drug was administered.

"There is this big question in the psychedelic therapy field right now about how much of this is a drug effect, how much of this is a therapy effect, and how much is a combination of the two," Davis said.

This study, the first to try to answer the question, found a drop in PTSD symptoms from baseline to the end of preparation therapy, with a much larger reduction after the psilocybin doses.

"This treatment is more than just a drug," Davis said. "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 research team acknowledges that pilot studies with no control group tend to produce larger effect sizes than standard clinical trials. They hope to secure funding to follow up with a larger randomized, controlled clinical trial.

"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. "Too many veterans right now are suffering despite the treatments that we have, and that's why we feel that this research is important."

Davis, who has been studying psychedelics as a component of mental health treatment for the past 16 years, said, "This is a very exciting time for psychedelic-assisted therapy research. These treatments are generally safe, well tolerated and showing a strong signal of efficacy."

This research was 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 of The Ohio State University Wexner Medical Center and Ohio State's College of Medicine.

Additional co-authors were Adam Levin, Nathan Sepeda, Hillary Shaub, Taweh Hunter, Angela Douglas and Rafaelle Lancelotta, all of Ohio State.