Efficacy and Safety of Psilocybin in Treatment-Resistant Major Depression

Psilocybin shows promise in treating depression, although limitations of previous research warrant further research.

To investigate the efficacy and safety of oral psilocybin, 25 mg, with adjunct psychotherapy in treatment-resistant depression (TRD). Design, Setting, and Participants: This was a 2-center, triple-blinded (investigator, participant, rater), phase 2b, active placebo-controlled randomized clinical trial. Participants were randomized to 4 groups in ratios 2:2:1:1, receiving 2 doses 6 weeks apart (week 0, week 6) as follows: (1) placebo (nicotinamide, 100 mg) then psilocybin, 25 mg; (2) psilocybin, 5 mg, then 25 mg; and (3) psilocybin, 25 mg, then 5 mg or psilocybin, 25 mg, twice embedded in psychotherapeutic sessions. Participants aged 25 to 65 years with TRD and withdrawn from antidepressant medication were recruited predominantly from 2 outpatient settings in Germany. Study data were analyzed from April 2024 to November 2025. Interventions: Oral synthetic psilocybin, 25 mg; psilocybin, 5 mg; or nicotinamide, 100 mg administered with psychotherapeutic sessions. Main Outcomes and Measures: The primary end point was treatment response (≥50% reduction on the Hamilton Rating Scale for Depression [HAMD17]) at week 6 before the second dose. Key secondary end points were response on the Beck Depression Inventory II (BDI-II) and mean change from baseline on the HAMD17 and BDI-II at week 6.