The, Gerard K H, Bleijenberg, Gijs, Buitelaar, Jan K et al. · The Journal of clinical psychiatry · 2010 · DOI
This study tested whether a medication called ondansetron, which affects serotonin signaling in the brain, could help reduce fatigue and improve daily functioning in people with ME/CFS. Sixty-seven patients took either ondansetron or a placebo pill for 10 weeks, and researchers measured changes in fatigue severity and ability to perform daily activities. The study found that ondansetron was no more helpful than placebo in reducing fatigue or improving function.
Although prior open-label studies suggested 5-HT3 antagonists might benefit ME/CFS patients, this rigorous randomized controlled trial provides important evidence against this treatment approach, preventing resources from being directed toward ineffective therapies. The study underscores the complexity of ME/CFS pathophysiology and the need for more mechanistic understanding before targeting specific neurochemical systems.
This negative trial does not prove that serotonin dysregulation plays no role in ME/CFS pathophysiology—only that blocking 5-HT3 receptors with ondansetron does not improve outcomes. It does not exclude the possibility that other serotonergic mechanisms or different patient subgroups might benefit from different interventions. The study also does not address whether treatment response might differ based on biomarkers or symptom profiles.
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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