What are the common toxic effects and symptoms of ivermectin overdose in adults?
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Executive summary
Ivermectin overdoses in adults commonly produce early gastrointestinal symptoms (nausea, vomiting, abdominal pain, diarrhea) and dose‑dependent neurologic effects ranging from dizziness and confusion to profound central nervous system (CNS) depression, seizures, coma and death; poison‑control and case‑series data show rapid symptom onset after large single doses or concentrated veterinary products [1] [2] [3]. Regulatory and clinical reports also list hypotension, visual disturbances and ataxia among frequent features, and management is largely supportive because there is no established antidote [4] [5] [6].
1. Gastrointestinal signs are often the first warning
Multiple public‑health summaries and case reports show that gastrointestinal complaints — nausea, vomiting, abdominal pain and diarrhea — are common early manifestations of ivermectin overdose and often precede neurologic deterioration [1] [5] [7]. The 2018 Cameroonian case described repeated vomiting and asthenia within 1–2 hours after ingestion of hundreds of tablets, illustrating how quickly GI symptoms can appear after very large doses [7].
2. Neurologic effects form the core of severe toxicity
Neurotoxicity is the dominant clinical concern in overdose: presentations range from headache, dizziness and ataxia to confusion, visual hallucinations, decreased consciousness, seizures, coma and respiratory failure in severe cases [2] [1] [4]. U.S. poison‑center case series linked veterinary‑product ingestions and supratherapeutic dosing to rapid onset of neurotoxicity, while toxicology reviews emphasize central nervous system depression as the key driver of morbidity [2] [8].
3. Hypotension, cardiac and respiratory complications increase risk of death
Government and toxicology advisories explicitly list hypotension and cardiorespiratory compromise among overdose sequelae; reports to poison centers and health advisories connect large ingestions with hypotension, respiratory failure and deaths in severe poisoning [4] [1] [8]. The fatal transdermal poisoning case and other reports document progression from GI and neurologic symptoms to cerebral edema, intracranial hypertension and death in extreme exposures [9].
4. Veterinary formulations and large single doses drive most severe events
Analyses and alerts repeatedly implicate veterinary ivermectin products — designed for large animals and concentrated — and large single or repeated supratherapeutic dosing as the major sources of human overdoses and rapid neurotoxicity [3] [2] [4]. The NEJM and poison‑center reviews described clusters where many patients obtained veterinary products and developed symptoms within hours of a large first dose [3] [2].
5. Symptom timing and patterns: acute vs. chronic exposure
Sources distinguish rapid, severe neurotoxicity after large single or short high‑dose regimens from milder, subacute patterns when people take typical therapeutic doses repeatedly for weeks; chronic toxicity more often produces milder neurologic or GI complaints, whereas massive doses produce profound CNS depression quickly [2] [8].
6. Visual, psychiatric and balance disturbances are commonly reported
Blurred vision, complex visual hallucinations, confusion and loss of coordination are documented across case reports and safety notices; Cureus and federal advisories describe visual hallucinations and complex perceptual disturbances as part of the ivermectin toxidrome [10] [1] [5].
7. No specific antidote; treatment is supportive and reactive
Available clinical literature and animal‑model work state there is no established antidote for ivermectin poisoning and that management is largely supportive (monitoring, airway/breathing/circulation, seizure control, symptomatic care); experimental adjuncts have been explored in research but are not standard of care [6] [8]. Poison control centers and public agencies instruct clinicians and the public to seek urgent medical evaluation and contact poison centers for management guidance [1].
8. Conflicting pressures: off‑label demand vs. safety communication
Multiple sources document that surges in human misuse were driven by interest in ivermectin for COVID‑19 prevention/treatment, fueling use of veterinary products and off‑label human prescriptions; public‑health advisories countered with warnings about overdose risks and lack of evidence for benefit [3] [5] [1]. This creates competing narratives: proponents cited small or preclinical studies, while regulators and poison centers pointed to rising harm from misuse [8] [5].
9. Practical takeaways for clinicians and the public
If someone reports taking excess ivermectin, especially veterinary formulations or very large doses, expect early GI symptoms and monitor closely for neurologic decline, hypotension, visual changes and seizures; call poison control and provide supportive care because no antidote exists [1] [4] [6]. Public sources urge avoiding self‑treatment with veterinary products and filling prescriptions only via legitimate human pharmacies [5].
Limitations and gaps: available sources summarize case series, advisories and case reports but do not provide a single comprehensive frequency table of each symptom by dose; laboratory thresholds correlating plasma ivermectin levels to specific clinical endpoints are inconsistently reported [9] [2]. Not found in current reporting: a universally accepted antidote or evidence‑based dose thresholds that reliably predict which patients will progress to respiratory failure.