Blinding and expectancy confounds in psychedelic randomised controlled trials
Open accessAbstract
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.
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From Potential therapeutic effects of an ayahuasca-inspired N,N-DMT and harmine formulation: a controlled trial in healthy subjects (2024) · cites this paper as [90]
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Flagged first, then by citations
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Cited by
Sorted by citations
Psychedelic-Assisted Psychotherapy—A Systematic Review of Associated Psychological Interventions
Cavarra, M., Falzone, A., Ramaekers, J. G., Kuypers, K. P. C., & Mento, C. (2022) · Frontiers in Psychology · doi:10.3389/fpsyg.2022.887255 · Cited by 171 · see citing works
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- Authors
- Muthukumaraswamy, S., Forsyth, A., & Lumley, T.
- Affiliations
- University of Auckland (NZ)
- Publisher
- Center for Open Science
- Published
- 2021-03-08
- OpenAlex
- W4231889404
- Cited by
- 15
- References
- 123
- Citations by year
- 2026: 2 · 2025: 1 · 2024: 3 · 2023: 2 · 2022: 4 · 2021: 3
- Type
- posted content
- Language
- en
- Open access
- green
- doi.org
- Licence
- Locations
- PsyArXiv (OSF Preprints) (submittedVersion, public-domain)
- PsyArXiv (OSF Preprints) (submittedVersion)
- Topics
- Social Sciences › Psychology › Clinical Psychology › Psychedelics and Drug Studies
- Life Sciences › Neuroscience › Cognitive Neuroscience › Pain Management and Placebo Effect
- Physical Sciences › Mathematics › Statistics and Probability › Statistical Methods in Clinical Trials
- Keywords
- psychedelics, blinding, response expectancy, placebo effect, psilocybin, LSD, ketamine, trial design, clinical trial reporting
About these checks
Registry, retraction, Cites and statistics results are computed, not judged, with one exception: a printed reference that no index lists is read once by a model before it counts as a citation error. Claims are extracted by a model and kept only when their quote appears verbatim in the text; each cited source is then checked, with a model’s help, for whether it says what the claim relies on. Those verdicts can be wrong — read the claim’s quote and the cited source before relying on one.
Statistics and arithmetic are recomputed, not judged.
Confidence bands are shown only for fields calibrated on our annotated test set. None is calibrated yet, so no band is shown.
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