Mathé, Philipp, Götz, Veronika, Stete, Katarina et al. · Infection · 2025 · DOI
Researchers compared serotonin levels in the blood of 34 people with long COVID (PASC) and 14 healthy people. Serotonin is a chemical in the body that affects mood and fatigue. The study found no meaningful difference in serotonin levels between the two groups, suggesting that low serotonin is probably not the main cause of long COVID symptoms.
This finding challenges the hypothesis that virally induced serotonin depletion drives PASC pathogenesis, which could redirect research toward alternative biological mechanisms. For patients, it suggests that low serotonin is unlikely a primary target, potentially preventing ineffective or unnecessary treatments and freeing resources for investigation of other ME/CFS-relevant pathways.
This study does not rule out serotonin dysfunction occurring at the synaptic or receptor level, only peripheral serum concentrations. It does not exclude serotonin as relevant in specific PASC subpopulations or in tissues other than blood. The cross-sectional design cannot determine whether serotonin changes precede PASC onset or whether temporal fluctuations in serotonin occur during illness.
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 →
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