What are documented cases and clinical outcomes of accidental human ingestion of veterinary ivermectin formulations?
Executive summary
A cluster of published case series and case reports documents accidental or intentional human ingestion of veterinary ivermectin formulations during the COVID-19 pandemic, with common clinical outcomes of neurotoxicity, gastrointestinal upset, and musculoskeletal complaints; severe presentations have required emergency department care and hospitalization in a minority of cases [1] [2] [3]. Toxicity tended to occur after doses well above human recommendations, often in older men using veterinary products for prevention or treatment of COVID‑19, and onset was frequently rapid when veterinary formulations were used [1] [2].
1. The documented cases: what was studied and who reported them
A multicenter case series compiled 40 patients reported to medical toxicology services over 15 months, of whom approximately half sought ivermectin for COVID‑19 prevention and half for treatment; within that cohort 17 patients ingested veterinary formulations and 15 took prescription human tablets [2] [1]. Parallel reporting from poison centers and clinicians—summarized in Clinical Toxicology and indexed on PubMed—describes rising calls during the pandemic documenting real-world exposures to veterinary ivermectin products and confirms that many exposures were self-medication rather than clinician-directed [4] [1].
2. Typical clinical presentations and severity
Across the published series, the dominant clinical syndrome was neurologic: confusion, ataxia and other neurotoxic signs were recorded in 30 of the reported 40 patients, while gastrointestinal symptoms (nausea, vomiting, abdominal pain, diarrhea) appeared in 14 and musculoskeletal complaints in seven [1] [2]. Regulatory and public‑health summaries list a broader spectrum of possible signs including headache, dizziness, visual disturbances, hypotension, altered mental status, and seizures, and note potentiation with other CNS‑depressant drugs [5].
3. Dose, formulation and timing matter
Patients who ingested veterinary ivermectin often did so in large single doses or repeated large daily doses over several days, and those patterns correlated with more rapid onset of neurotoxicity compared with typical human dosing patterns [1] [2]. Case descriptions and poison‑center data show reported ingested amounts from veterinary pastes and solutions ranging widely (for example, 6.8 mg to 125 mg from paste products in one series), underlining that product concentration and formulation (paste, pour‑on, injectable) complicate dose estimation [3] [6].
4. Severe outcomes, hospitalizations and rare complications
A subset of exposed patients required emergency care: in one NEJM‑reported cluster, six of 21 persons were hospitalized for toxic effects, and larger series reported multiple ED presentations with 19 hospital admissions among 40 patients in the clinical toxicology report [3] [2]. Case reports document more unusual routes—such as intravenous administration of veterinary ivermectin in a COVID‑19 patient—producing pronounced neurotoxicity but not invariably fatal outcomes, while pharmacokinetic discussion notes ivermectin’s potential to persist in brain tissue and prolonged metabolite half‑life that can slow recovery [7].
5. What mechanisms and product differences explain harm?
Pharmacologic analyses emphasize that veterinary products differ in concentration, excipients and intended species, and that human safety data derive from weight‑based oral tablets approved for parasitic diseases—differences that can increase risk when animal formulations are consumed by people [8] [9]. Toxicology summaries further stress that co‑medications that depress the central nervous system may worsen effects, and that the elimination half‑life of ivermectin metabolites (~3 days) can prolong clinical course [5] [7].
6. Limits of the record and competing interpretations
Available literature is largely case series, poison‑center reports and isolated case reports rather than randomized data, so incidence and risk estimates are imperfect and skew toward clinically significant exposures that prompted medical attention [2] [4]. Alternative viewpoints in the literature emphasize ivermectin’s established safe use in humans at approved doses for parasitic infections [10], and researchers caution that small accidental exposures can be benign while larger off‑label doses—especially from veterinary formulations—carry demonstrable risk [10] [1].
7. Bottom line for clinicians and public health
Documented human ingestions of veterinary ivermectin formulations have produced a reproducible pattern of neurotoxicity and gastrointestinal symptoms, sometimes requiring hospitalization, particularly after high or repeated doses; the evidence derives from poison‑center surveillance, clinical toxicology case series and case reports and is consistent across those sources [1] [2] [3]. Public‑health guidance and toxicology reviews therefore discourage any use of veterinary ivermectin in humans and recommend seeking medical care for suspected toxic ingestion, while acknowledging that small accidental exposures have at times been asymptomatic in older case series [5] [10].