E2 ModerateModerate confidencePEM not requiredCase-ControlPeer-reviewedReviewed
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Contrasting neuroendocrine responses in depression and chronic fatigue syndrome.
Cleare, A J, Bearn, J, Allain, T et al. · Journal of affective disorders · 1995 · DOI
Quick Summary
This study compared hormone levels and brain chemistry in people with ME/CFS, people with depression, and healthy controls. The researchers found that people with ME/CFS had lower cortisol (a stress hormone) and higher responses to a serotonin-related chemical, which is the opposite pattern seen in depression. This suggests ME/CFS and depression are biologically different conditions despite sometimes sharing similar symptoms like fatigue.
Why It Matters
This research provides biological evidence that ME/CFS and depression are distinct conditions with opposite neuroendocrine abnormalities, which helps validate ME/CFS as a separate disease and may guide future treatment approaches. Understanding these biological differences is important because ME/CFS and depression are sometimes conflated clinically, potentially leading to inappropriate treatment.
Observed Findings
Baseline cortisol levels were significantly lowest in CFS, highest in depression, and intermediate in healthy controls (P = 0.01).
Prolactin responses to d-fenfluramine were significantly highest in CFS, lowest in depression, and intermediate in healthy controls (P = 0.01).
Matched pair analysis confirmed higher prolactin responses in CFS vs. controls (P = 0.05) and lower responses in depression vs. controls (P = 0.003).
Strong inverse correlations were observed between prolactin responses and cortisol levels in all groups.
Inferred Conclusions
CFS is associated with hypocortisolaemia and increased central serotonin function, contrasting with the hypercortisolaemia and reduced serotonin function observed in depression.
The opposing neuroendocrine patterns in CFS and depression may reflect reversed patterns of behavioral dysfunction between the two conditions.
These findings establish biological distinctions between CFS and depression at the neuroendocrine level.
Remaining Questions
Do these neuroendocrine abnormalities fluctuate over time or remain stable, and do they correlate with symptom severity or progression in CFS?
What are the upstream causes of low cortisol and elevated serotonin function in CFS—are they central nervous system, hypothalamic, or adrenal in origin?
What This Study Does Not Prove
This study does not prove that low cortisol or altered serotonin function *cause* ME/CFS symptoms—it only shows an association. The cross-sectional design cannot establish causality or determine whether these hormonal changes are primary drivers of illness or secondary consequences. A single d-fenfluramine challenge does not fully characterize serotonergic function across different brain regions and time points.
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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