What are the documented risks and side effects of taking veterinary ivermectin?
Executive summary
Veterinary ivermectin has been linked in case reports and public-health warnings to toxic overdoses, neurologic effects (dizziness, confusion, seizures, ataxia), gastrointestinal symptoms (nausea, vomiting, diarrhea, abdominal pain), and allergic/dermatologic reactions; several U.S. poisonings and hospitalizations were associated with people using veterinary formulations during the COVID‑19 era [1] [2] [3]. Veterinary products differ in concentration, formulation, and excipients from human tablets, and using large‑animal doses in people risks serious harm because those formulations are designed for species and weights very different from humans [4] [5].
1. Why people use veterinary ivermectin — and why that raises risk
During the COVID‑19 pandemic and afterward some people sought ivermectin as a perceived antiviral despite randomized trials showing no clinical benefit; that demand pushed people toward veterinary formulations (horse paste, injectable livestock solutions) that contain the same active ingredient but different concentrations, delivery vehicles and inactive ingredients—creating a high risk of accidental overdose or toxic exposure in humans [1] [6] [5].
2. Documented acute toxic effects in humans
Clinics and case series document neurologic and gastrointestinal toxicity after ingestion of veterinary ivermectin: reported signs include dizziness, confusion, ataxia (difficulty moving), seizures and sleepiness, alongside nausea, vomiting, diarrhea and abdominal pain; several exposures required hospitalization and at least some fatal outcomes were linked in media reporting and case surveillance [1] [2] [3].
3. Why neurologic symptoms occur at high doses
Ivermectin acts on glutamate‑gated chloride channels and can affect mammalian GABA receptors at high levels or when the drug crosses into the central nervous system; veterinary overdoses or inappropriate dosing increase blood levels enough to produce neurotoxicity—explaining reports of encephalopathy, ataxia and seizures in overdoses [4] [7] [8].
4. Reported dose ranges and real‑world poisonings
Case reports compiled by clinicians show people who used veterinary paste or solutions swallowed doses that ranged widely (examples in reports include pastes of 1.87% and solutions of 1%), and hospitalized patients had ingested quantities far above standard human dosing; in one NEJM series, reported veterinary product doses ranged from small milligram amounts up to much larger exposures and six of 21 people were hospitalized [1].
5. Animal‑formulation hazards beyond the active drug
Veterinary syringes, pastes and injectables are formulated for large animals and may contain solvents, stabilizers or concentrations unsuitable for humans; manufacturers’ and regulatory guidance warn that animal products can be dangerous if used by people and should not enter watercourses or be handled carelessly—underscoring that formulation differences create distinct safety concerns [9] [10] [5].
6. Species and genetic vulnerabilities — why some animals (and possibly people) fare worse
In veterinary practice certain dog breeds with an MDR1 genetic mutation are far more sensitive to ivermectin and experience neurologic toxicity at doses tolerated by other dogs; this underlines that genetic and physiologic differences change safety margins and that extrapolating animal dosing to humans is unsafe [7] [4].
7. Common, milder side effects with correct human dosing
When used as approved in humans, ivermectin commonly causes milder effects such as fever, itching, rash, red or dry eyes for topical use, and occasional systemic effects like dizziness, nausea or diarrhea—side effects that are well described in human product information but differ from overdose toxicity seen with veterinary misuse [11] [12].
8. Public‑health signals and regulatory warnings
U.S. and other health authorities documented increases in poison‑control calls and prescriptions for ivermectin during the pandemic; medical centers and articles cautioned against using veterinary formulations to treat COVID‑19, and public‑facing health pieces repeat that benefits for COVID‑19 are unproven while risks from animal products are documented [1] [2] [13].
9. Treatment and clinical context for suspected poisoning
Clinical management of ivermectin toxicity is supportive; severe veterinary overdoses have required hospitalization and, in veterinary medicine, treatments such as intralipid emulsion have been used experimentally for severe neurologic poisoning in animals—human-specific antidotes are not standard and management focuses on supportive care [8] [1]. Available sources do not mention a standardized antidote approved for humans.
10. What the reporting gaps and limitations are
Published series and media reports document poisonings, but available sources do not provide a comprehensive population‑level incidence of adverse events from veterinary ivermectin misuse; randomized trials addressing efficacy for COVID‑19 failed to show benefit for human formulations, and available reporting focuses on case series, regulatory warnings and veterinary literature rather than controlled human overdose trials [6] [1] [13].
Bottom line: veterinary ivermectin is the same active molecule as prescription human ivermectin but packaged, concentrated and formulated for animals; misuse of animal products has caused documented poisonings with neurologic and gastrointestinal effects and hospitalizations, and health authorities warn against using animal ivermectin for human conditions [5] [1] [3].