Cited by 324Psychedelics and Drug StudiesPain Management and Placebo EffectStatistical Methods in Clinical Trials

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Blinding and expectancy confounds in psychedelic randomized controlled trials

Muthukumaraswamy, Suresh D., Forsyth, Anna, Lumley, Thomas·2021·Expert Review of Clinical Pharmacology

DOI 10.1080/17512433.2021.1933434

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Abstract

Introduction: There is increasing interest in the potential for psychedelic drugs such as psilocybin, LSD and ketamine to treat several mental health disorders, with a growing number of randomized controlled trials (RCTs) being conducted to investigate the therapeutic effectiveness of psychedelics.Areas covered: We review previous literature on expectancy effects and blinding in the context of psychedelic RCTs – literature which strongly suggest that psychedelic RCTs might be confounded by de-blinding and expectancy. We conduct systematic reviews of psychedelic RCTs using Medline, PsychInfo and EMBASE (Jan 1990 – Nov 2020) and show that currently reported psychedelic RCTs have generally not reported pre-trial expectancy, nor the success of blinding procedures.Expert opinion: While psychedelic RCTs have generally shown promising results, with large effect sizes reported, we argue that treatment effect sizes in psychedelic RCTs are likely over-estimated due to de-blinding of participants and high levels of response expectancy. We suggest that psychedelic RCTs should routinely measure de-blinding and expectancy. Careful attention should be paid to clinical trial design and the instructions given to participants to allow these confounds to be reduced, estimated and removed from effect size estimates. We urge caution in interpreting effect size estimates from extant psychedelic RCTs.

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Retracted
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Authors: Muthukumaraswamy, S. D., Forsyth, A., & Lumley, T.
Affiliations: University of Auckland (NZ)
Corresponding author: Muthukumaraswamy, Suresh D.
ORCID: Muthukumaraswamy, Suresh D.
Forsyth, Anna
Lumley, Thomas
Venue: Expert Review of Clinical Pharmacology
Publisher: Informa UK Limited
Published: 2021-08-26
Volume: 14
Issue: 9
Pages: 1133-1152
ISSN: 1751-2433 (ISSN-L)
1751-2441
DOI: 10.1080/17512433.2021.1933434
OpenAlex: W3164618783
Cited by: 324
References: 128
Citations by year: 2026: 57 · 2025: 75 · 2024: 81 · 2023: 61 · 2022: 42 · 2021: 8
FWCI: 6.38
Type: journal article
Language: en
Open access: closed
Locations: Expert Review of Clinical Pharmacology (publishedVersion)
PubMed (publishedVersion)
Funders: Health Research Council of New Zealand
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, confounding, psilocybin, LSD, ketamine, effect size overestimation, trial design, mental illness
MeSH terms: Mental Disorders, Hallucinogens, Humans, Ketamine, Lysergic Acid Diethylamide, Psilocybin, Research Design, Confounding Factors, Epidemiologic, Randomized Controlled Trials as Topic

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Blinding and expectancy confounds in psychedelic randomized controlled trials

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