Cho, Hyong Jin, Hotopf, Matthew, Wessely, Simon · Psychosomatic medicine · 2005 · DOI
This study looked at how often ME/CFS patients improve simply from believing they will improve (the placebo effect) in clinical trials. Researchers found that the placebo response in ME/CFS is actually lower than many people assume—only about 20% of patients improved with placebo. Interestingly, patients were less likely to show placebo improvement when the treatment was psychological or psychiatric in nature, possibly because many ME/CFS patients believe their illness is physical rather than mental.
This study corrects a widespread misconception that ME/CFS treatment responses are primarily due to placebo effects, which has sometimes been used to dismiss patient symptoms as psychosomatic. Understanding the actual magnitude and determinants of placebo response helps distinguish genuine therapeutic effects from expectancy-driven improvement, strengthening the scientific basis for evaluating future ME/CFS treatments. The finding that patient beliefs about intervention type influence placebo response also has implications for trial design, informed consent, and communication strategies in ME/CFS research.
This meta-analysis does not prove that ME/CFS is primarily physical or psychiatric in nature—it only shows that patients' preexisting beliefs about causation influence their placebo response. The study also does not establish that the 20% placebo response is uniform across all ME/CFS patients or trial designs, as significant heterogeneity existed. Finally, a low placebo response does not indicate that psychological interventions are ineffective; it only suggests that improvement in psychological trials is less driven by expectancy alone.
About the PEM badge: “PEM required” means post-exertional malaise was an explicit required diagnostic criterion for participant inclusion in this study — not that PEM was studied, observed, or discussed. Studies using criteria that do not require PEM (e.g. Fukuda, Oxford) are tagged “PEM not required”. How the atlas works →
The first block is for the primary paper and is the citation you should use in research work. The atlas-snapshot line only applies if you are specifically referring to this atlas’s reading of the paper on the date shown.
Primary citation
Cho, Hyong Jin, Hotopf, Matthew, & Wessely, Simon (2005). The placebo response in the treatment of chronic fatigue syndrome: a systematic review and meta-analysis.. Psychosomatic medicine. https://doi.org/10.1097/01.psy.0000156969.76986.e0
BibTeX
@article{mecfsatlas-cho-2005-placebo-response,
author = {Cho, Hyong Jin and Hotopf, Matthew and Wessely, Simon},
title = {The placebo response in the treatment of chronic fatigue syndrome: a systematic review and meta-analysis.},
journal = {Psychosomatic medicine},
year = {2005},
doi = {10.1097/01.psy.0000156969.76986.e0},
note = {PubMed: 15784798},
url = {https://www.mecfsatlas.com/evidence/cho-2005-placebo-response},
}Atlas snapshot reference
ME/CFS Atlas. Generator v1 / Scanner v1.4 / policy v0.1. Accessed 2026-05-26. https://www.mecfsatlas.com/evidence/cho-2005-placebo-response
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