What is known – with real numbers where they exist – about serotonin, dopamine, glutamate, GABA, acetylcholine, norepinephrine, and histamine in Long COVID (PASC)
| Measure | Class | Group | Mean | Approx. IQR | Approx. Range | N |
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These neurotransmitter/neuromodulator systems have real, cited evidence of altered function in Long COVID, but the published studies report significance, prevalence, or single-arm values rather than a matched mean±SD pair suitable for a box plot. Evidence tier reflects how solid the finding is, not how large the effect looks.
Type-I-interferon-driven inflammation reduces gut tryptophan absorption, platelet hyperactivation depletes the body's main serotonin store, and MAO turnover increases – all plausible routes to lower circulating serotonin. Disrupted vagal signaling from this is proposed to impair hippocampal function, contributing to brain fog, memory problems, and fatigue.
Caveat: the most-cited quantitative study (Wong et al., Cell 2023) has been challenged on methodological grounds – incomplete platelet depletion may have inflated absolute values 30–60× above biological plausibility (Andres et al., J Inflamm Res 2024). A separate cohort of 457 controls found no significant serotonin reduction. The direction (lower in Long COVID) is plausible and mechanistically supported; the exact magnitude is not settled.
Intracortical inhibitory (GABAergic) signaling appears impaired in post-acute COVID syndrome, measured via MEGA-PRESS MRS in occipital cortex. Combined with excess glutamate, this points toward a cortical excitation/inhibition imbalance that may underlie hyperarousal, anxiety, and reduced inhibition of excitatory signaling.
Data: Long COVID (n=18) had significantly lower occipital GABA+/water ratio than controls (n=20), F(1,33)=6.15, p=0.018. Exact means are reported only in a figure, not extractable as text.
A 2025 review proposes cholinergic dysfunction – via impaired nicotinic acetylcholine receptor (nAChR) signaling – as a potentially central mechanism, since cholinergic tone modulates the release of dopamine, serotonin, glutamate, and GABA. This could help explain the overlapping symptom pattern (cognition, dysautonomia, fatigue) shared across Long COVID and ME/CFS.
Data: The one case-control study with a quantitative autoantibody assay (anti-muscarinic receptor M3, n=100 Long COVID vs n=20 controls) did not reach statistical significance (p>0.05), though a related beta2-adrenergic receptor autoantibody trended toward elevation (p=0.0634). Reported here transparently rather than selectively.
Signs of catecholamine dysregulation are well-documented in Long COVID dysautonomia, particularly the POTS-like phenotype: orthostatic intolerance, palpitations, and autonomic imbalance, plausibly linked to endothelial dysfunction and altered cerebral blood flow.
Data: No matched case-control study with clean mean±SD plasma/CSF norepinephrine (Long COVID vs healthy controls) was found. A deep-phenotyping study found 38% of Long-COVID-POTS patients (n=24) met the >600 pg/mL standing norepinephrine threshold that clinically defines "hyperadrenergic POTS" – a subset finding, not a population mean comparison.
Mast cell activation syndrome (MCAS) or mast cell hyperactivation is prevalent in a subset of Long COVID patients, plausibly driving neuroinflammation, allergic-type symptoms, cardiovascular issues, GI problems, brain fog, and fatigue. Many patients report symptomatic improvement with H1/H2 antihistamines, which is suggestive but not diagnostic of a histamine-driven mechanism.
Data: No verified case-control study with matched mean±SD plasma histamine (Long COVID vs healthy controls) was found. Elevated histamine (case series, ~34% of tested patients) and MCAS-consistent symptom prevalence are documented, but not as a population-level quantitative comparison.