Efficacy of Psilocybin-Assisted Therapy in Major Depressive Disorder: A Systematic Review and Meta-Analysis

Background: This systematic review and meta-analysis evaluates the efficacy and safety of psilocybin-assisted psychotherapy (PAP) for adults with major depressive disorder (MDD). Methods: A PROSPERO-registered search (CRD42024561979) of CENTRAL, Scopus, PsycINFO, and MEDLINE (2010-2024) identified clinical trials assessing PAP. Risk of bias was assessed using RoB 2 for randomized controlled trials (RCTs), while non-randomized studies were appraised separately. Evidence certainty was evaluated using GRADE. Results: Ten trials were included; eight provided quantitative data. PAP was associated with large short-term reductions in depressive symptom severity. The overall pooled effect was large (d = 1.15, 95% CI0.83-1.48), though within-subject designs yielded larger estimates (d = 1.63) than between-subject controlled comparisons (d = 0.96). Adverse events were transient and manageable, with no increased risk of serious adverse events on dosing days. Primary risk-of-bias concerns included functional unblinding. Conclusions: PAP may produce clinically meaningful, large short-term reductions in depressive symptoms. However, long-term efficacy remains understudied, and the overall certainty of evidence is low to moderate. Larger, rigorously blinded trials are required.