Psilocybin Therapy Shows Limited Benefit in Treatment-Resistant Depression: JAMA
Germany: A new phase IIb EPISODE trial revealed that psilocybin combined with psychotherapy failed to meet the primary endpoint in treatment-resistant depression. Some secondary outcomes showed improvement, but results may be influenced by expectancy bias, common in psychedelic trials. A systematic review and meta-analysis found that psychedelic-assisted therapy was not superior to open-label conventional antidepressant treatment.
A randomized clinical trial published in JAMA Psychiatry by Lea J. Mertens from Heidelberg University and colleagues further explored the therapeutic potential of psilocybin in individuals with treatment-resistant depression (TRD). While earlier research has suggested promising antidepressant effects, methodological concerns and limited data have necessitated more rigorous evaluation.
This phase IIb, triple-blinded, active placebo-controlled trial enrolled 144 adults aged 25 to 65 years with TRD who had discontinued antidepressant medications. Conducted across two centers in Germany, participants were assigned to different treatment groups receiving oral synthetic psilocybin at doses of 25 mg or 5 mg, or an active placebo (nicotinamide 100 mg), administered alongside structured psychotherapeutic sessions. Two dosing sessions were conducted six weeks apart.
The primary endpoint was defined as a treatment response—at least a 50% reduction in depression severity based on the Hamilton Rating Scale for Depression (HAMD-17)—measured at six weeks before the second dose.
The key findings from the EPISODE trial were as follows:
- No statistically significant difference in response rates was observed between the high-dose psilocybin group and the placebo group.
- Response rates were 17.0% with psilocybin 25 mg compared to 10.6% with placebo.
- Secondary outcome analyses indicated potential clinical benefits with psilocybin 25 mg.
- Greater reductions in depressive symptoms were seen on both HAMD-17 and Beck Depression Inventory-II scores in the psilocybin 25 mg group.
- These findings suggest possible antidepressant effects despite the negative primary outcome.
- Psilocybin was generally well-tolerated among participants.
- Adverse events were mostly acute and occurred around the time of dosing sessions.
- A higher incidence of suicidal ideation was reported on dosing days in the high-dose psilocybin group compared to controls.
- Two serious adverse reactions were reported, including one case of hallucinogen persisting perception disorder.
- The safety findings highlight the importance of careful monitoring during treatment.
The authors highlighted several limitations, including the possibility of functional unblinding, which may have influenced patient expectations and outcomes. The relatively small sample size, short follow-up duration, and homogeneity of the study population may also limit the generalizability of the findings. Additionally, the absence of long-term data prevents conclusions about sustained efficacy and safety.
Overall, while the trial did not achieve its primary objective, it contributed valuable evidence to the evolving field of psychedelic-assisted therapy. The findings suggest that psilocybin, when combined with psychotherapy, may offer some benefit in reducing depressive symptoms in TRD, but larger and more robust trials are needed to confirm its role in clinical practice.
Reference:
Mertens LJ, Koslowski M, Betzler F, et al. Efficacy and Safety of Psilocybin in Treatment-Resistant Major Depression: The EPISODE Randomized Clinical Trial. JAMA Psychiatry. Published online March 18, 2026. doi:10.1001/jamapsychiatry.2026.0132
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