What are documented symptoms and outcomes of ivermectin overdose in humans?
Executive summary
Ivermectin overdoses in humans are documented to cause mainly neurological effects — confusion, decreased consciousness, ataxia, seizures and coma — plus gastrointestinal complaints (nausea, vomiting, diarrhea) and cardiopulmonary or circulatory collapse in severe cases; poison-center series reported dozens of exposures with hospitalizations and at least one death in a multi-center compilation [1] [2] [3]. Most contemporary reports tie severe events to large, off-label doses or veterinary formulations intended for large animals; chronic lower‑dose misuse more often produced milder, gradual symptoms [2] [4].
1. A clear pattern: neurotoxicity is the dominant syndrome
Multiple clinical summaries and poison‑center case series describe a toxidrome dominated by central‑nervous‑system effects — altered mental status, confusion, hallucinations, ataxia, tremor, seizures and even coma — occurring within hours of large, first‑time ingestions or over days to weeks of repeated misuse [2] [5] [3]. Regulatory agencies list dizziness, ataxia and seizures among overdose outcomes and warn that encephalopathy and respiratory depression can occur in severe poisonings [1] [5].
2. Gastrointestinal and systemic signs are common but usually secondary
Public‑health advisories and clinical reviews repeatedly note nausea, vomiting and diarrhea as common features of ivermectin overdose; hypotension and allergic reactions (pruritus, hives) are also described and have been reported in surveillance and advisory notices [6] [1] [7]. In poison‑center data, gastrointestinal complaints accompanied the neurologic presentations in a substantial minority of patients [2].
3. Severity tracks with dose, formulation and patient factors
Reports show the worst outcomes when people ingested highly concentrated veterinary products intended for horses or cattle — those formulations deliver far higher milligram doses and sometimes include excipients not studied in humans [6] [2] [4]. Case series also identify host vulnerabilities: older patients predominated in some cohorts, and genetic or drug‑interaction mechanisms (ABCB1/ P‑glycoprotein variants or drugs that inhibit it) plausibly allow ivermectin to cross the blood‑brain barrier and produce severe neurotoxicity [8] [9].
4. Real‑world case counts, hospitalizations and deaths
Surveillance during the COVID‑era documented spikes in exposures. A poison‑center series identified 37 cases over 24 weeks with most patients older (median age 64), many hospitalized or treated in emergency departments , and one death reported in that cohort [2]. Earlier letters and reports from the Oregon Poison Center and the CDC described 21 calls in August 2021 with six hospitalizations; symptoms frequently developed within two hours after a large single dose [3] [10].
5. Management: no antidote, supportive care only
Authors and toxicology reviews emphasize there is no specific antidote for ivermectin; treatment is supportive and driven by the clinical problems (airway, seizure control, hemodynamic support). Poison centers and medical sites advise contacting regional poison control and seeking emergency care for severe symptoms [5] [11] [12].
6. How mis/disinformation shaped who got harmed
A surge in off‑label use driven by social and political discourse around COVID‑19 boosted demand, prescriptions and veterinary‑product misuse; public‑health agencies explicitly warned that ivermectin is not authorized to treat COVID‑19 and cautioned against animal formulations — “you are not a horse” became a public admonition from regulators [6] [1] [13]. Reporting shows that many exposures were attempts at prevention or treatment of COVID‑19 rather than approved parasitic indications [2] [3].
7. Limits of available reporting and open questions
Existing sources are largely case series, poison‑center reports and agency advisories; they document what symptoms occurred and correlate severity with dose and formulation, but do not define a precise human LD50 or a complete therapeutic window in varied clinical contexts [14] [8]. Genetic susceptibility (ABCB1 variants) and drug‑drug interactions are plausible contributors but remain incompletely quantified in population studies [8] [9].
8. Practical takeaway for clinicians and the public
If ivermectin ingestion is suspected and any neurological, respiratory or circulatory symptoms develop, contact poison control immediately and arrange urgent evaluation; there is no antidote and outcomes depend on rapid supportive care [11] [5]. Public guidance from the FDA and CDC is consistent: approved human uses exist at weight‑based doses for specific parasitic diseases, but not for COVID‑19 — misuse of veterinary products carries documented risk [1] [6].
Sources used: CDC/FDA advisories and news summaries [6] [1], poison‑center and clinical toxicology case series [2] [3] [4], clinical reviews and toxicology analyses on manifestations, mechanisms and management [5] [8] [11].