What are the reported symptoms and outcomes of ivermectin toxicity in humans from veterinary formulations?
Executive summary
Reports and clinical reviews identify a consistent pattern: ingestion of veterinary ivermectin formulations—often in much higher doses than human prescriptions—has produced primarily neurologic and gastrointestinal illness in people, with a spectrum ranging from mild, self-limited symptoms to severe altered mental status, seizures and hospitalization; management is supportive because there is no specific antidote [1] [2] [3]. Veterinary products carry higher concentrations, non‑pharmaceutical excipients, and dosing intended for large animals, which helps explain why exposures to those formulations are overrepresented among more severe cases [4] [5].
1. The clinical picture: what patients report and what hospitals see
Case series and poison‑center summaries list neurotoxicity as the dominant manifestation—confusion, altered mental status, ataxia/loss of coordination, dizziness and, in some cases, seizures—followed by gastrointestinal complaints such as nausea, vomiting, abdominal pain and diarrhea; musculoskeletal complaints (e.g., weakness, myalgias) are also reported [1] [2] [3]. Visual disturbances including blurred vision and visual hallucinations have been documented in surveillance reports, and central nervous system depression leading to stupor or coma appears in the more severe presentations [2] [3].
2. Why veterinary formulations are riskier than human tablets
Veterinary ivermectin is manufactured in pastes, injectables or high‑concentration liquids for animals weighing hundreds to thousands of pounds, so a small administered quantity can deliver far more active drug per kilogram to a person than a human prescription; regulators and clinicians emphasize that veterinary products may also include solvents, fillers or delivery vehicles not tested for human ingestion, increasing unpredictability of effects [4] [3] [5]. Reports show patients taking veterinary products tended to ingest larger single or repeated doses and had higher rates of altered mental status than those taking human‑formulation tablets [1].
3. Dose, kinetics and the blood–brain barrier
Toxicity correlates with dose: animal data and clinical guidance suggest toxicity in animal models often at doses of several mg/kg, while poison‑control guidance flags >2 mg/kg as a threshold warranting hospital evaluation; at higher concentrations ivermectin can cross the blood–brain barrier and produce the neurologic toxicity observed in people [6]. Chronic use at lower daily doses over weeks has produced milder but persistent symptoms compared with the abrupt, high‑dose ingestions typically linked to veterinary product misuse [1].
4. Outcomes, severity and health‑system impact
Outcomes range from transient nausea and dizziness to severe neurologic compromise requiring hospitalization; published case series and public‑health advisories document hospital admissions and intensive observation for severe CNS depression or seizures, though the reviewed sources do not provide a quantified death rate for veterinary‑formulation exposures [1] [2] [3]. Surveillance during COVID‑19 showed a clear increase in human exposures and poison‑center calls related to ivermectin, reflecting both greater misuse and a corresponding burden on emergency services [2] [3].
5. Treatment approach and limitations
There is no ivermectin‑specific antidote: management is supportive and symptom‑directed, including seizure control, airway support if necessary, and monitoring of vital signs and neurologic status; early consultation with poison control or clinical toxicology services is routinely recommended [3]. Because veterinary preparations may contain unknown excipients, clinicians often monitor more closely and treat based on clinical effect rather than predictable pharmacology alone [3].
6. The contested context and lingering unknowns
While ivermectin is an FDA‑approved antiparasitic for certain human uses, major health agencies do not endorse veterinary ivermectin for COVID‑19 and warn against self‑medication; proponents who tout ivermectin’s benefits represent an alternative viewpoint that has driven demand and misuse, but clinical surveillance and toxicology reports repeatedly link veterinary product ingestion to more severe adverse events [4] [7] [5]. The literature establishes typical symptom patterns and management principles, but available reports vary in size and detail, and sources used here do not uniformly quantify long‑term outcomes or mortality after veterinary‑formulation exposures [1] [2] [3].