Are there any reported cases of ivermectin-induced neurological disorders in humans?
Executive summary
Published case series and pharmacovigilance studies document human neurological adverse events after ivermectin, including confusion, ataxia, seizures, stupor/coma and encephalopathy; some reports link these events to Loa loa coinfection, overdose, blood–brain barrier compromise, or P‑glycoprotein dysfunction [1] [2] [3]. Large programmatic experience notes encephalopathies primarily in persons heavily infected with Loa loa during mass ivermectin campaigns [4] [5].
1. What has been reported — a catalogue of neurological events
Researchers and safety databases list nervous‑system events after ivermectin ranging from common, mild effects (dizziness, headache, somnolence, tremor) to severe events including confusion, ataxia, seizures, stupor and coma; case reports and series describe encephalopathy and fatal outcomes in a minority of cases [2] [6] [3] [5].
2. Where the strongest evidence comes from — onchocerciasis/Loa loa programmes
The clearest, repeatedly documented pattern links severe neurological events to mass ivermectin treatment in areas co‑endemic for Onchocerca volvulus and high Loa loa microfilarial loads: outbreaks of post‑treatment encephalopathy with coma were recorded in Central Africa and analyzed in programmatic studies [4] [5]. These programmatic reports remain the principal source tying ivermectin‑timed neurologic catastrophe to a specific epidemiological context [4] [5].
3. Case series beyond onchocerciasis — pharmacovigilance flags
A published case series and searches of global spontaneous‑report databases yielded dozens of suspected serious neurological adverse drug reactions after ivermectin for indications other than onchocerciasis; within those reports investigators found supportive evidence in some instances — e.g., drug detected in brain tissue in one case and symptom recurrence on re‑exposure in three cases — suggesting causality cannot be dismissed [1] [7].
4. Mechanisms proposed — P‑glycoprotein, dose, and blood–brain‑barrier
Authors point to biologic mechanisms that would permit ivermectin to reach and act on central nervous system targets: normally P‑glycoprotein at the blood–brain barrier limits brain penetration, but genetic variants or functional impairment (or very high exposure/overdose) can permit accumulation and GABA‑ergic potentiation that produces neurotoxicity — this mechanism is supported by animal models and human case discussion [4] [7] [8].
5. The COVID‑19 era and inappropriate use — more reports, different patterns
During the COVID‑19 pandemic and afterwards, case series and monitoring reports documented emergency presentations after inappropriate or veterinary ivermectin use, describing severe confusion, ataxia, seizures and hypotension requiring hospitalization; authors emphasise misuse, overdosing and interactions as likely contributors [3] [2].
6. Frequency and risk context — rare but real, concentrated in specific settings
Systematic pharmacovigilance work finds neurological serious adverse events are uncommon relative to the millions treated, but clustering occurs where Loa loa burden is high or when dosing and formulations are aberrant; programmatic studies in the DRC and pharmacovigilance reviews identified hundreds of neurologic SAE in outbreak settings, often dominated by coma [5] [2].
7. Clinical and public‑health implications — screening and caution
Public‑health guidance from the literature recommends pre‑treatment assessment for loaiasis in endemic areas, careful dosing, and vigilance for drug interactions or conditions that might disrupt the blood–brain barrier; some authors stress that single, standard antiparasitic doses used appropriately remain widely tolerated, while higher exposures and off‑label use increase risk [4] [9] [2].
8. What the sources disagree on or leave open
Investigators debate whether all reported non‑onchocerciasis neurologic events are caused by ivermectin itself, by coinfections like Loa loa, by concomitant CNS‑active drugs, or by accidental overdose; the case series notes confounders in many reports and acknowledges that causation is not always established [7] [1]. Available sources do not mention definitive population‑level incidence estimates for neurological injury from ivermectin outside those outbreak contexts.
9. Bottom line for clinicians and patients
Documented cases show ivermectin can be associated with severe neurologic events in humans; the strongest, repeatable signal is encephalopathy after treatment in people with high Loa loa microfilarial loads, but case reports and pharmacovigilance data also record serious events linked to overdose, formulation misuse, or likely blood‑brain barrier/P‑glycoprotein issues [4] [1] [3]. Clinicians should follow local guidelines, screen where recommended, avoid non‑recommended high dosing or veterinary products, and report suspected adverse events to pharmacovigilance systems [2] [3].
Limitations: this summary uses only the provided sources and does not attempt to adjudicate causality beyond what those reports state; where assertions are not in the supplied material, they are noted as not found in current reporting [1] [2].