E3 PreliminaryPreliminaryPEM unclearReview-NarrativePeer-reviewedMachine draft
Evaluation of central serotonergic function in affective and related disorders by the fenfluramine challenge test: a critical review.
Newman, Michael E., Shapira, Baruch, Lerer, Bernard · The international journal of neuropsychopharmacology · 1998 · DOI
Quick Summary
This review examines a test called the fenfluramine challenge test, which measures how well the brain's serotonin system is working by looking at prolactin levels after taking fenfluramine. The researchers found that people with depression typically had a blunted (reduced) prolactin response, and that some people with chronic fatigue syndrome might have had an enhanced response, though not many studies existed in this group.
Why It Matters
This review is relevant to ME/CFS research because it identifies preliminary evidence that people with chronic fatigue syndrome may show altered serotonergic function (enhanced prolactin responses) compared to healthy controls and depressed patients. Understanding whether ME/CFS involves serotonin system dysfunction could help researchers develop targeted treatments and distinguish ME/CFS from depression, which share overlapping symptoms.
Observed Findings
- - Healthy subjects show dose-dependent prolactin release following fenfluramine that is blocked by serotonin receptor antagonists
- - Major depression is consistently associated with blunted prolactin responses compared to healthy controls
- - Blunted prolactin responses correlate with impulsive aggression and severity of suicide attempts in depressed patients
- - Prolactin responses may be enhanced in panic disorder and chronic fatigue syndrome, but few studies exist in these conditions
- - Antidepressant treatment and electroconvulsive therapy inconsistently normalize prolactin responses
Inferred Conclusions
- - Central serotonergic function appears reduced in major depression, as evidenced by blunted prolactin responses
- - Serotonergic dysfunction may be associated with specific behavioral phenotypes (impulsive aggression, suicidality) rather than being disease-specific
- - Chronic fatigue syndrome may involve a different serotonergic profile (possible enhancement) compared to depression, though evidence is limited and requires replication
Remaining Questions
- - Do enhanced prolactin responses in CFS reflect true serotonergic hyperfunction or a different neurobiological mechanism?
- - What is the mechanistic relationship between altered serotonergic responses and the cardinal symptoms of ME/CFS (post-exertional malaise, cognitive dysfunction)?
What This Study Does Not Prove
This review does not establish that serotonin dysfunction causes ME/CFS—it only describes associations in a small number of studies. The limited data in ME/CFS patients means conclusions about this population remain preliminary and speculative. Additionally, because fenfluramine is no longer available clinically, these findings cannot be directly confirmed with new research using the same method.
Tags
Symptom:Fatigue
Biomarker:Blood Biomarker
Method Flag:Exploratory Only
Metadata
- DOI
- 10.1017/S1461145798001072
- PMID
- 11281946
- Review status
- Machine draft
- Evidence level
- Early hypothesis, preprint, editorial, or weak support
- Last updated
- 10 April 2026
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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