What doses of ivermectin are considered toxic in humans and what symptoms appear?
Executive summary
High, non‑therapeutic doses of ivermectin — especially veterinary formulations or repeated supratherapeutic human dosing — have been linked repeatedly to neurologic and gastrointestinal toxicity including confusion, ataxia, seizures, coma and even death; chronic self‑treatment cases described daily doses around 13.5 mg over weeks and acute veterinary‑product ingestions produced more severe altered mental status [1] [2]. Regulatory and public‑health reports warn that taking large or animal‑grade ivermectin is dangerous and that approved human dosing is a single dose roughly 0.15–0.2 mg/kg for parasitic infections [3] [2].
1. What counts as “toxic” doses in humans — no single universal threshold
There is no single, universally accepted human “toxic dose” number in the provided reporting; toxicity has occurred both after large single ingestions of veterinary products and after prolonged, repeated human dosing. A case series and poison‑control analyses show chronic users taking smaller daily doses (median daily dose reported ~13.5 mg over ≈3.8 weeks) developed toxicity that was milder than acute ingestions; patients who took veterinary formulations typically ingested very large single doses and developed rapid, severe neurologic effects [1]. Standard approved single human doses are far lower — generally weight‑based at about 0.15–0.2 mg/kg — and commonly used regimens are several times smaller than amounts implicated in reported toxicities [3] [4].
2. Why veterinary formulations amplify risk
Veterinary ivermectin products are formulated and concentrated for large animals; these formulations differ from human tablets and can contain much higher amounts per dose and different inactive ingredients. The FDA and other public health authorities explicitly warn that animal products are not tested for human safety and that using them can be dangerous — many overdose reports involve veterinary products [2] [5] [6]. Poison‑control centers and CDC advisories tied spikes in severe cases during the COVID‑19 period to people ingesting animal products bought without prescriptions [2] [7].
3. Typical clinical picture: neurologic plus gastrointestinal effects
Across case series and public‑health advisories, ivermectin toxicity presents mainly with neurologic and gastrointestinal symptoms. Neurologic signs include confusion, decreased consciousness or coma, ataxia/loss of coordination, tremor, seizures and hallucinations; gastrointestinal complaints include nausea, vomiting and diarrhea. Cardiovascular instability (hypotension) and respiratory compromise have also been reported in severe overdoses [1] [8] [9] [10].
4. Dose ranges in animal data and how they relate to humans
Animal LD50 data vary by species; mice and dog LD50s cited in pharmacologic summaries suggest very large mg/kg amounts relative to approved human dosing, yielding a wide approximated human‑equivalent LD50 range in some summaries — but such extrapolations are contextual, not clinical safety limits for people [11]. The practical takeaway from reporting and case reviews is that human toxicity correlates with ingestion patterns (large single doses or repeated supra‑therapeutic dosing), co‑ingested CNS depressants, and use of non‑human formulations — not a neat single mg/kg cutoff [1] [12].
5. Special clinical contexts that increase danger
Three important contexts raise risk: heavy Loa loa parasitic infection or onchocerciasis can cause severe neurologic adverse events after ivermectin (a known treatment complication), co‑administration with other drugs that depress the central nervous system can worsen toxicity, and compromised blood‑brain barrier states (sepsis, certain illnesses) may permit ivermectin brain penetration and serious encephalopathy [12] [9] [11].
6. Public‑health evidence of harm and scale of reports
Pharmacovigilance and surveillance reporting rose markedly during the COVID‑19 period: analyses found thousands of adverse‑event notifications tied to ivermectin, including hundreds classified as severe and multiple deaths or life‑threatening outcomes; reviewers and major journals concluded off‑label use provided no benefit and carried risk [13] [14]. U.S. poison centers and the CDC documented increased calls for ivermectin exposures tied to misuse [7] [8].
7. What the available reporting does not say
Available sources do not give a single unambiguous mg/kg threshold that will always cause toxicity in humans; they also do not provide exhaustive pharmacokinetic cutoffs usable clinically for every patient [1] [11]. Sources do not claim that modest approved, single‑dose human treatments routinely cause neurologic catastrophe; instead, harms cluster with misuse, high cumulative dosing, or veterinary product ingestion [3] [2] [1].
Summary recommendation based on reporting: follow approved, prescription dosing (about 0.15–0.2 mg/kg for indicated parasitic infections) and never use veterinary formulations; seek immediate medical help for symptoms such as confusion, loss of coordination, seizures, severe nausea/vomiting, breathing problems or loss of consciousness because case reports and public‑health advisories document those as key features of ivermectin toxicity [3] [2] [1] [8].