Meta-analysis · 2026
Placebo groups in psychedelic trials also improved, but less than treatment groups
- Original title
- Magnitude of response in treatment and control groups within psychedelic trials for psychiatric disorders: A meta-analysis.
- Authors
- Meshkat S, Lin Q, Sousa-Ho R, et al.
- Journal
- European psychiatry : the journal of the Association of European Psychiatrists, 2026
- Molecules
- Other
- Conditions
- Depression, PTSD, Anxiety
- Participants
- 643
- Evidence grade
- Moderate
- Source
- Read the original paper
The question
How much do people in the placebo or control arms of psychedelic trials improve, and how does that compare with the improvement seen in the groups that received the drug?
What they did
Researchers searched the literature up to 1 July 2025 for randomized controlled trials of psychedelic-assisted psychotherapy in psychiatric disorders, following a protocol registered in advance. Fourteen trials with a total of 643 participants were included. They pooled the differences between treatment and control arms, and also described how much symptoms changed from baseline within each arm separately.
What they found
Treatment groups improved more than control groups across outcomes: depressive symptoms (13 study arms, standardized mean difference -0.82, 95% confidence interval -1.17 to -0.47), post-traumatic stress disorder symptoms (10 arms, SMD -0.89, 95% CI -1.14 to -0.65) and anxiety symptoms (5 arms, SMD -0.66, 95% CI -0.94 to -0.38). Statistical inconsistency between studies was high for depression (I2 = 60.1%) but absent for PTSD and anxiety (I2 = 0%). Control groups also showed substantial symptom reductions from baseline, with the largest PTSD improvements seen in inactive placebo groups. There was limited evidence that results differed depending on the type of placebo used.
The fine print
The pooled sample of 643 people across 14 trials is small for a meta-analysis, and some outcomes drew on only five study arms. The within-group (baseline-to-endpoint) findings were descriptive, so they cannot separate drug effects from natural recovery over time. Results for depression varied considerably between studies, and the abstract does not say which substances, doses or disorders were included. This summary is based on the abstract only.
What it means
Psychedelic treatments outperformed control conditions in these trials, but people receiving placebo also improved noticeably, which suggests expectations and the accompanying psychotherapy contribute to the results. That makes careful control conditions and cautious interpretation of headline effect sizes important.
Evidence grade: Moderate. A preregistered meta-analysis of 14 randomized controlled trials, but the pooled sample is modest, some outcomes rest on few study arms, and the within-group comparisons are descriptive only.
This summary is based on the study’s published abstract.