Williams, G, Waterhouse, J, Mugarza, J et al. · European journal of clinical investigation · 2002 · DOI
This study tested whether melatonin pills and bright light therapy could help ME/CFS patients feel better. Thirty patients tried both treatments (and a placebo) for 12 weeks each. Neither treatment improved fatigue, physical health, mental health, or mood compared to placebo, even though both are sometimes recommended for ME/CFS.
Many ME/CFS patients are offered melatonin and light therapy by practitioners based on the theory that circadian disruption drives symptoms. This high-quality RCT provides evidence that these widely-prescribed interventions do not benefit ME/CFS patients, helping prevent unnecessary or ineffective treatment and redirecting research toward more promising therapeutic targets.
This study does not prove that circadian rhythm disturbances do not occur in ME/CFS, only that correcting them with melatonin or phototherapy does not improve symptoms. It also does not rule out the possibility that subgroups of patients with specific circadian profiles might benefit, nor does it exclude the potential value of other circadian interventions not tested here.
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
Williams, G, Waterhouse, J, Mugarza, J, Minors, D, & Hayden, K (2002). Therapy of circadian rhythm disorders in chronic fatigue syndrome: no symptomatic improvement with melatonin or phototherapy.. European journal of clinical investigation. https://doi.org/10.1046/j.1365-2362.2002.01058.x
BibTeX
@article{mecfsatlas-williams-2002-therapy-circadian,
author = {Williams, G and Waterhouse, J and Mugarza, J and Minors, D and Hayden, K},
title = {Therapy of circadian rhythm disorders in chronic fatigue syndrome: no symptomatic improvement with melatonin or phototherapy.},
journal = {European journal of clinical investigation},
year = {2002},
doi = {10.1046/j.1365-2362.2002.01058.x},
note = {PubMed: 12423324},
url = {https://www.mecfsatlas.com/evidence/williams-2002-therapy-circadian},
}Atlas snapshot reference
ME/CFS Atlas. Generator v1 / Scanner v1.4 / policy v0.1. Accessed 2026-05-30. https://www.mecfsatlas.com/evidence/williams-2002-therapy-circadian
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