Blinding and Expectancy Confounds in Psychedelic Randomised Controlled Trials

This systematic review (2021) argues that de-blinding (breaking blind) in randomized controlled trials (RCTs) of psychedelic therapies is leading to a (not defined/measurable) over-estimation of the outcomes (outside clinical trials). The authors suggest measures to tackle this and to use caution interpreting the existing RCTs.


“There is increasing interest in the potential for psychedelic drugs such as psilocybin, LSD and ketamine to treat a number of mental health disorders. To gain evidence for the therapeutic effectiveness of psychedelics, a number of randomised controlled trials (RCTs) have been conducted using the traditional RCT framework and these trials have generally shown promising results, with large effect sizes reported. However, in this paper we argue that estimation of treatment effect sizes in psychedelic clinical trials are likely over-estimated due to de-blinding of participants and high levels of response expectancy generated by RCT trial contingencies. The degree of over-estimation is at present difficult to estimate. We conduct systematic reviews of psychedelic RCTs and show that currently reported RCTs have failed to measure and report expectancy and malicious de-blinding. In order to overcome these confounds we argue that RCTs should routinely measure de-blinding and expectancy and that careful attention should be paid to the clinical trial design used and the instructions given to participants to allow these confounds to be estimated and removed from effect size estimates. We urge caution in interpreting effect size estimates from extant psychedelic RCTs.”

Authors: Suresh Muthukumaraswamy, Anna Forsyth & Thomas Lumley


Eduardo Schenberg has also responded to this article with a letter to the editor.

Find this paper

Blinding and Expectancy Confounds in Psychedelic Randomised Controlled Trials

Open Access | Google Scholar | Backup | 🕊

Published in
Expert Review of Clinical Pharmacology
August 26, 2021
0 citations

Study details