Smith, Simon, Sullivan, Karen · International journal of behavioral medicine · 2003 · DOI
This study tested whether cognitive problems (like difficulty concentrating) in people with ME/CFS are caused by actual chemical exposure or by what people believe they are being exposed to. Thirty-six patients were given either a placebo or a chemical trigger while not knowing which one they received, and their thinking ability was tested before and after. The results showed that cognitive performance got worse when patients thought they had been exposed to a chemical, regardless of what they actually received.
Cognitive dysfunction is one of the most distressing and disabling symptoms of ME/CFS. This study provides evidence that psychological factors—specifically beliefs about chemical exposure—may modulate cognitive performance, potentially opening doors to psychological interventions that could help some patients manage or reduce cognitive symptoms.
This study does not prove that cognitive problems in ME/CFS are purely psychological or 'not real.' It does not establish causation—only that attributions about exposure correlate with test performance. The findings apply specifically to acute cognitive responses to perceived chemical exposure and may not explain all cognitive symptoms in ME/CFS or longer-term cognitive decline.
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
Smith, Simon & Sullivan, Karen (2003). Examining the influence of biological and psychological factors on cognitive performance in chronic fatigue syndrome: a randomized, double-blind, placebo-controlled, crossover study.. International journal of behavioral medicine. https://doi.org/10.1207/s15327558ijbm1002_05
BibTeX
@article{mecfsatlas-smith-2003-examining-influence,
author = {Smith, Simon and Sullivan, Karen},
title = {Examining the influence of biological and psychological factors on cognitive performance in chronic fatigue syndrome: a randomized, double-blind, placebo-controlled, crossover study.},
journal = {International journal of behavioral medicine},
year = {2003},
doi = {10.1207/s15327558ijbm1002_05},
note = {PubMed: 12763708},
url = {https://www.mecfsatlas.com/evidence/smith-2003-examining-influence},
}Atlas snapshot reference
ME/CFS Atlas. Generator v1 / Scanner v1.4 / policy v0.1. Accessed 2026-05-26. https://www.mecfsatlas.com/evidence/smith-2003-examining-influence
Contribute
Private, reviewed by a human. Not a public comment thread.