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What are the risks and clinical signs of ivermectin overdose in humans and in animals, and how are overdoses managed?
Executive summary
Ivermectin overdoses in humans most often produce gastrointestinal and neurologic effects — nausea, vomiting, diarrhea, dizziness, confusion, ataxia, seizures, coma and in rare reports death — and public-health agencies warn veterinary formulations (highly concentrated) pose special risk to people [1] [2] [3]. In animals, toxicity varies by species and genetics (notably ABCB1/P-gp mutations in dogs) and can cause neurologic depression, coma and death; treatment is mainly supportive because there is no specific elimination procedure such as dialysis [4] [5] [6] [7].
1. What happens in a human ivermectin overdose: the clinical picture
Health agencies and drug reference sites describe a consistent cluster of symptoms in humans after overdose: gastrointestinal upset (nausea, vomiting, diarrhea), cardiovascular effects like hypotension, and neurologic signs ranging from dizziness, confusion, hallucinations and ataxia (balance problems) to seizures, decreased consciousness and coma; rare fatal outcomes have been reported [1] [2] [8] [9].
2. Why veterinary products are especially dangerous for people
Veterinary ivermectin formulations are concentrated and dosed for large animals (horses, cattle), so a human consuming those products can receive multi‑fold overdoses compared with approved human dosing; multiple agencies warned against using animal products in people during COVID‑19, and poison‑center calls rose sharply when people self‑medicated with veterinary ivermectin [1] [3] [10].
3. Species differences: how animals react and why genetics matter
Ivermectin toxicity varies widely across species. Most mammals are protected by P‑glycoprotein (P‑gp) at the blood‑brain barrier; animals lacking functional P‑gp (or certain dog breeds with ABCB1/MDR1 mutations such as collies) are prone to neurotoxicity — drowsiness, ataxia, coma and death — even at lower doses [4] [5] [11]. Laboratory LD50 figures also differ by species, underscoring variable susceptibility [6].
4. Mechanism of harm: how ivermectin causes toxicity
Ivermectin’s antiparasitic action targets glutamate‑gated chloride channels in invertebrates; at high systemic levels or when CNS exclusion is compromised, it can affect mammalian GABA and other chloride channels, producing central nervous system depression and downstream problems such as respiratory depression or seizures. P‑gp at the blood‑brain barrier normally pumps the drug out; dysfunction of that mechanism increases risk [12] [4].
5. How overdoses are managed in people: medical approaches and limits
Clinical management of ivermectin overdose in humans is largely supportive: monitor vitals, airway/breathing/circulation, treat seizures, provide IV fluids for hypotension, and manage complications in intensive care if needed. Poison‑control centers and emergency services are the recommended contacts; authoritative sources emphasize there is no simple elimination method such as dialysis — metabolism and time are key to clearance [13] [2] [7].
6. How overdoses are managed in animals: veterinary practice
Veterinary management also centers on supportive care: decontamination if ingestion is recent (e.g., activated charcoal in some contexts), intravenous fluids, symptomatic treatment, and monitoring; topical exposures may require washing the coat. Prognosis depends on species, dose, and whether the animal has an ABCB1 mutation; severe cases can be fatal or lead to euthanasia decisions [5] [6].
7. Frequency, reporting and public‑health context
Poison centers reported marked increases in ivermectin exposure calls during the COVID‑19 period, driven in part by off‑label and veterinary product use; public‑health messaging from FDA, CDC and states warned against self‑medicating with animal products and noted spikes in prescriptions and exposures [1] [10] [2].
8. What reporting gaps and disagreements remain
Available sources document clinical signs, species differences, and supportive management, but do not supply a universally agreed “overdose dose” cutoff for humans (available sources do not mention a single human toxic threshold). Studies and reviews differ on long‑term organ effects and on the detailed pharmacokinetic modifiers in vulnerable patients; some animal toxicology LD50 numbers vary by study and species [6] [11] [14].
9. Practical takeaways and where to get help
Do not use veterinary ivermectin for people; follow prescription dosing for human formulations and consult a clinician. If overdose or serious symptoms occur, contact local emergency services or your regional poison control center (U.S. 800‑222‑1222) immediately — agencies and clinical guides advise urgent evaluation and supportive care [13] [2] [10].
Limitations: this summary uses the provided reporting and reviews; it does not attempt to adjudicate every disputed therapeutic claim about ivermectin’s efficacy against diseases beyond approved antiparasitic uses (available sources discuss but do not support ivermectin as COVID‑19 therapy) [15] [16].