Compass Pathways has released peer-reviewed results from a Phase 2 study testing its investigational synthetic psilocybin therapy, COMP360, in patients with post-traumatic stress disorder (PTSD).
The findings, now published in the Journal of Psychopharmacology, indicate that a single 25 mg dose of COMP360, combined with psychological support, was safe, well tolerated, and linked to significant and lasting symptom improvements for many participants.
The international study, conducted at three sites in the U.K. and U.S., enrolled 22 patients. According to Compass, participants demonstrated rapid symptom reduction that remained durable for 12 weeks after treatment. Importantly, no serious adverse events were reported, an encouraging outcome in a field where treatment innovation has lagged.
“Affecting approximately 13 million people in the U.S., and with only two approved treatments in the past two decades, post-traumatic stress disorder represents an area of profound unmet need,” said Dr. Guy Goodwin, Compass’s Chief Medical Officer. “Based on the highly encouraging results, we are finalizing late-stage clinical trial designs and look forward to evaluating the full potential of COMP360 for the treatment of PTSD.”
The trial found that COMP360 was generally well tolerated. The most common side effects included headache (50%), nausea (36.4%), crying and fatigue (27.3% each), and visual hallucinations (22.7%). None of these rose to the level of serious or treatment-emergent events.
In terms of efficacy, the trial used the CAPS-5 scale, the gold standard for assessing PTSD severity. From a mean baseline score of 47.5, participants showed a 29.9-point reduction by week 4 and a 29.5-point reduction by week 12. That level of improvement is considered both clinically meaningful and durable.
Functional impairment, measured by the Sheehan Disability Scale (SDS), also improved significantly. Average scores fell from 22.7 at baseline to 11.0 at week 4 and 8.3 at week 12. These reductions suggest that patients not only experienced fewer PTSD symptoms but were also better able to engage in daily life.
The rates of response and remission were striking. Response—defined as a reduction of 15 points or more on the CAPS-5—was achieved by 81.8% of participants at week 4 and remained high at 77.3% at week 12. Remission, defined as a CAPS-5 score of 20 or lower, was reached by 63.6% of participants at week 4 and 54.5% at week 12.
PTSD affects around 5% of U.S. adults annually, with higher rates among veterans, first responders, and survivors of violence or disaster. The condition is marked by intrusive memories, avoidance, negative mood changes, and heightened arousal. It often co-occurs with depression, anxiety, and substance use disorders, further complicating treatment.
Currently, only two medications—sertraline and paroxetine—are approved by the FDA for PTSD. Many patients do not respond adequately, leaving psychotherapy and off-label prescriptions as the main options. This limited toolkit underscores the urgency for new, effective therapies.
The results of Compass Pathways’ psilocybin study suggest that psychedelic-assisted treatments could offer a breakthrough. By targeting both the underlying trauma and its emotional impacts, psilocybin therapy has the potential to reshape mental health care for PTSD.
Compass Pathways, headquartered in London with offices in New York, is developing COMP360 psilocybin therapy for multiple indications, including treatment-resistant depression (TRD) and PTSD. The therapy has already been granted Breakthrough Therapy designation by the FDA for TRD and Innovative Licensing and Access Pathway status in the U.K.
The company’s model involves pairing a single dose of its proprietary synthetic psilocybin with guided psychological support. This approach is designed to maximize both safety and therapeutic benefit.
The newly published PTSD results build on Compass’s ongoing research in depression and mark another step toward potential regulatory approval. While Phase 2 data are promising, larger late-stage trials will be necessary to confirm safety and efficacy before COMP360 can be considered for widespread clinical use.
If successful, psilocybin therapy could represent one of the first major innovations in PTSD treatment in decades. For the millions living with the condition—and for the clinicians treating them—the Phase 2 results provide reason for cautious optimism that a new, more effective option may soon be on the horizon.
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