A dose of therapy with psilocybin - A meta-analysis of the relationship between the amount of therapy hours and treatment outcomes in psychedelic-assisted therapy.

Psilocybin-assisted therapy (PAT) has shown promising effects in treating depressive symptoms, but the role of the therapeutic component remains unclear. While most research has focused on the pharmacological effects of psilocybin, the contribution of therapy has been largely overlooked. This meta-analysis investigated whether the amount of therapy hours provided is associated with treatment outcomes in psilocybin-assisted therapy for depression. A systematic search of PubMed and PsycINFO yielded 1095 records. Sixteen studies met inclusion criteria, providing sufficient data for analysis. A meta-regression was conducted to assess the relationship between therapy hours and treatment outcomes. The overall treatment effect was large both in the short-term (Cohen's d = 1.69) and long-term follow-up (Cohen's d = 2.10). However, no significant association was found between the number of therapy hours and outcome in either the short-term (b = −0.05, p =.327) or long-term (b = −0.07, p =.340) analyses. All of the included studies provided some degree of therapy (4.5–18 h). Our findings did not support that the amount of therapy hours influence depressive outcomes in PAT. However, this interpretation should be made with caution due to small sample sizes, heterogeneity, and poor reporting of the therapeutic component across studies. Future research should apply greater methodological rigor and standardized reporting of therapy to clarify its role in PAT. • Psilocybin-assisted therapy yielded large effect sizes for reduction in depressive symptoms. • Meta-regression revealed no statistically significant association between the amount of therapy hours and treatment outcomes. • Interpretability was limited due to inadequate reporting and lack of standardized therapy protocols. • Findings underscore the need for methodological rigor and broader investigation of the role of the therapeutic component.