Vassallo, C M, Feldman, E, Peto, T et al. · Psychological medicine · 2001 · DOI
This study examined whether people with ME/CFS have oversensitive serotonin receptors in the brain, which could explain some of their symptoms. Researchers gave patients and healthy people a drug that directly activates serotonin receptors and measured the response. They found that both groups responded similarly, suggesting the problem in ME/CFS is not overly sensitive receptors but rather increased serotonin activity from nerve cells themselves. Interestingly, people with ME/CFS had lower levels of tryptophan (a building block for serotonin) in their blood.
Understanding the biological basis of serotonin dysfunction in ME/CFS could guide targeted treatments. This study narrows the mechanism by showing the problem lies upstream in serotonin-producing neurons rather than in the receptors that receive the signal, potentially redirecting therapeutic approaches.
This study does not establish whether the serotonin abnormality is a cause of ME/CFS symptoms or a consequence of the illness. It also does not explain why tryptophan is low or whether increasing tryptophan would improve symptoms. The findings are correlational and limited to measuring prolactin and sleep responses in a laboratory setting.
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
Vassallo, C M, Feldman, E, Peto, T, Castell, L, Sharpley, A L, & Cowen, P J (2001). Decreased tryptophan availability but normal post-synaptic 5-HT2c receptor sensitivity in chronic fatigue syndrome.. Psychological medicine. https://doi.org/10.1017/s0033291701003580
BibTeX
@article{mecfsatlas-vassallo-2001-decreased-tryptophan,
author = {Vassallo, C M and Feldman, E and Peto, T and Castell, L and Sharpley, A L and Cowen, P J},
title = {Decreased tryptophan availability but normal post-synaptic 5-HT2c receptor sensitivity in chronic fatigue syndrome.},
journal = {Psychological medicine},
year = {2001},
doi = {10.1017/s0033291701003580},
note = {PubMed: 11352361},
url = {https://www.mecfsatlas.com/evidence/vassallo-2001-decreased-tryptophan},
}Atlas snapshot reference
ME/CFS Atlas. Generator v1 / Scanner v1.4 / policy v0.1. Accessed 2026-05-30. https://www.mecfsatlas.com/evidence/vassallo-2001-decreased-tryptophan
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