Control groups in psychedelic-assisted psychotherapy trials show substantial symptom improvement, likely due to non-specific factors such as expectancy and concurrent psychotherapy. A meta-analysis of 14 randomized controlled trials (643 participants) found that treatment groups had greater symptom reductions than control groups for depressive symptoms, PTSD symptoms, and anxiety symptoms. For PTSD, inactive placebo groups showed larger within-group improvements. The findings underscore the need for robust control conditions and careful interpretation of treatment effects in psychedelic research.
Low-dose psilocybin, given as 1–3 mg or 0.1–0.2 g of dried mushrooms, shows limited and inconsistent evidence for treating mental disorders. In two randomized controlled trials for treatment-resistant depression, 18% of participants receiving 1 mg showed a significant response, 8% achieved remission, and depression scores improved by −5.4 points at week 3, but only 10% maintained improvement by week 12. Another trial reported no significant improvement with 1–3 mg, though 12% achieved anxiety remission and 16% depression remission. A trial comparing 25 mg to 1 mg plus escitalopram found higher response rates with the higher dose. The evidence is constrained by few well-designed studies comparing low-dose psilocybin to placebo.