Do two psychedelic dosing sessions beat one? A review of 23 depression and anxiety trials

The question

Does the number of psychedelic dosing sessions, or the type of talk therapy given alongside them, change how well psychedelic-assisted psychotherapy works for depression and anxiety?

What they did

The researchers searched for all published clinical trials of psychedelic-assisted psychotherapy in which the main outcome was symptoms of a depressive or anxiety disorder. Twenty-three studies met their criteria. They then tested two possible moderators: how many dosing sessions participants received, and whether the accompanying psychotherapy was drawn from an established, evidence-based therapy model or not.

What they found

Across the studies, psychedelic-assisted psychotherapy showed large to very large effects at the end of treatment and at follow-up, with Hedge’s g values ranging from 0.98 to 1.83 (a standard measure of effect size, where anything above roughly 0.8 is considered large). When trials were compared against their control groups, two dosing sessions appeared to work better than one. That pattern did not hold up in the analysis that looked at change within groups over time. Only three studies used psychotherapy protocols based on established evidence-based therapies, too few to test that question.

The fine print

The abstract does not report the total number of participants pooled across the 23 studies, nor which psychedelics were used. The authors note that many trials lacked blinded outcome assessment and did not follow intention-to-treat analysis, both of which inflate apparent benefit. The two-session finding was not consistent across the two types of analysis, so it should be treated as preliminary. This summary is based on the abstract only.

What it means

Pooled trial data suggest psychedelic-assisted psychotherapy produces large improvements in depression and anxiety symptoms, but the evidence is weakened by unblinded assessment, and the hint that two dosing sessions outperform one needs direct testing before it can guide practice.

Evidence grade: Moderate. A systematic review and meta-analysis, but it pools trials of differing designs and the authors flag unblinded outcome assessment and analysis problems that raise the risk of bias.

This summary is based on the study’s published abstract.