Compass Pathways: Extra COMP360 Dose Extends Relief to 1 Year

Compass Pathways Reports Yearlong Data From a Second Psilocybin Dose

Compass Pathways, a biotechnology company developing COMP360, a proprietary synthetic form of psilocybin given alongside psychological support, announced on September 9, 2026, that 52-week topline open-label data from its Phase 3 COMP005 trial show an additional benefit when participants received a second dose of COMP360 during an extension phase called Part C, according to the company's company announcement. COMP005 is one of two pivotal Phase 3 trials evaluating COMP360 for treatment-resistant depression (TRD), a form of major depressive disorder that has not responded to at least two prior antidepressant treatments. Part C is an open-label extension arm, meaning every participant in this phase knew they were receiving COMP360, with no placebo comparison group, and received a repeat dose after the initial trial period. According to Compass Pathways, the new data extend evidence of durability out to one year following the additional dose.

This is topline data, a preliminary summary release that precedes full statistical analysis and independent peer review. The company has not yet published a full data set or a peer-reviewed manuscript alongside this announcement, based on the information available at this time.

What the Open-Label Design Means for How Much Weight to Give This Result

An open-label trial design, where both patients and researchers know who received the active treatment, cannot rule out placebo effect or expectation bias, which are well documented in psychedelic-assisted therapy research generally. Part C data should be read as a description of what happened to people who already knew they were taking COMP360, not as proof that the compound alone caused the reported improvement. That distinction matters most for readers deciding how much weight to put on the one-year durability finding.

Compass Pathways has previously reported blinded, placebo-controlled results from the earlier stages of its COMP360 development program, including a Phase 2b trial, so the company has run controlled comparisons elsewhere in its pipeline. This particular 52-week release, however, is specifically an open-label extension result, and the two study designs answer different questions: the controlled trials test whether COMP360 outperforms placebo, while Part C tests what happens over time once everyone is on active treatment and some receive a second dose.

Redosing itself is also a meaningful variable. The finding that a second dose of COMP360 in Part C was associated with additional benefit, as the company describes it, raises practical questions about how often psilocybin-assisted therapy might need to be repeated to sustain effect, which mirrors an active debate in ketamine treatment about maintenance dosing intervals.

Why This Matters to Ketamine Patients and Families

COMP360 is psilocybin, not ketamine, and Compass Pathways is pursuing a separate regulatory pathway for TRD. But the two therapies sit in the same broader category of psychedelic-assisted or dissociative-assisted mental health treatment, and developments in one program often shape how clinics, insurers, and regulators talk about the other. If COMP360 eventually secures approval, patients weighing ketamine therapy may face a genuinely new comparison point on cost, dosing frequency, and durability of effect, rather than ketamine being the only psychedelic-adjacent option available through a licensed provider.

For now, there is no approved psilocybin therapy available outside clinical trials in the United States, and COMP360 remains investigational. Readers currently considering or receiving ketamine therapy for depression should not change their treatment plan based on this announcement. The practical takeaway is narrower: this data point suggests researchers across the psychedelic medicine field are actively studying redosing schedules and long-term durability, questions that are equally relevant to ketamine maintenance protocols. Anyone in ongoing ketamine treatment who is thinking about dosing frequency or long-term maintenance should raise that question directly with their prescribing clinician rather than drawing conclusions from a separate compound's trial data.

Patients interested in following COMP360's trajectory should watch for Compass Pathways to release full COMP005 results and, eventually, submit the trial for regulatory review, since only that fuller data set and an independent regulatory assessment will clarify how reliable the 52-week durability signal is.