Raij, Tommi, Raij, Kari · Frontiers in endocrinology · 2024 · DOI
This study examined whether a supplement called L-carnitine could help reduce fatigue by increasing serotonin levels in the blood. Researchers tracked 12 people with ME/CFS and 40 people with hypothyroidism who were experiencing fatigue, measuring their serotonin and fatigue levels before and after taking L-carnitine for 7 weeks. They found that L-carnitine increased serotonin levels significantly and fatigue decreased by about half in both groups, suggesting a possible connection between low serotonin and fatigue.
For ME/CFS patients, this study offers preliminary evidence of a biological mechanism linking low peripheral serotonin to fatigue and suggests L-carnitine as a potential therapeutic intervention. Understanding biochemical pathways underlying fatigue is critical for developing targeted treatments in conditions where fatigue persists despite standard care, addressing a major unmet clinical need.
This study does not prove that L-carnitine causes fatigue reduction or that low serotonin causes ME/CFS fatigue—it only shows correlation. The small sample size, absence of a placebo control group, and retrospective design prevent definitive causal conclusions. Results cannot be generalized to the broader ME/CFS population without prospective, randomized controlled trials.
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
Raij, Tommi & Raij, Kari (2024). Association between fatigue, peripheral serotonin, and L-carnitine in hypothyroidism and in chronic fatigue syndrome.. Frontiers in endocrinology. https://doi.org/10.3389/fendo.2024.1358404
BibTeX
@article{mecfsatlas-raij-2024-association-between,
author = {Raij, Tommi and Raij, Kari},
title = {Association between fatigue, peripheral serotonin, and L-carnitine in hypothyroidism and in chronic fatigue syndrome.},
journal = {Frontiers in endocrinology},
year = {2024},
doi = {10.3389/fendo.2024.1358404},
note = {PubMed: 38505756},
url = {https://www.mecfsatlas.com/evidence/raij-2024-association-between},
}Atlas snapshot reference
ME/CFS Atlas. Generator v1 / Scanner v1.4 / policy v0.1. Accessed 2026-05-25. https://www.mecfsatlas.com/evidence/raij-2024-association-between
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