What medical complications occur from people ingesting veterinary ivermectin for horses?
Executive summary
Emergency departments and poison-control centers reported spikes in human exposures to veterinary ivermectin during the COVID-19 pandemic; published case series and reviews link ingestion of veterinary products to neurologic effects (seizure, coma), gastrointestinal upset, hypotension and liver problems, with some hospitalizations reported [1] [2] [3]. Veterinary ivermectin formulations are far more concentrated and formulated for animals (pastes, injectables), so accidental or intentional human ingestion can produce overdoses and cumulative toxicity [4] [5].
1. Veterinary formulations are different and concentrated — the overdose risk is real
Veterinary ivermectin comes as concentrated pastes and injectables intended for large animals; those formulations and doses are not designed for human use and have resulted in overdoses when people ingest them. News and academic reporting note that animal products (horse paste, cattle injectables) are concentrated and can produce toxic doses in humans, especially when taken repeatedly rather than as a single medically supervised dose [4] [5] [6].
2. Neurologic effects: the most commonly reported severe harms
Clinical series and poison-center reports document neurologic toxicity as a dominant manifestation after misuse of veterinary or excess human ivermectin — confusion, ataxia, seizures and coma have been reported. A PubMed case series found toxicity mainly in older men who took higher-than-recommended doses and developed neurologic symptoms; NEJM case reporting also lists hospitalization for toxic neurologic effects among those using veterinary products [1] [2].
3. Gastrointestinal, hepatic and systemic reactions documented
Reports from academic medical centers and hospital physicians describe severe gastrointestinal upset as common, and UCLA clinicians and poison-control summaries cite liver problems and liver failure among reported complications from misuse. The New England Journal of Medicine report also documents multiple hospitalizations from toxic effects after preventive or repeated dosing [3] [2].
4. Cardiovascular collapse and life‑threatening presentations have occurred
Older toxicology reviews and case reports note that large ingestions of avermectins (the class that includes ivermectin) can produce hypotension and life‑threatening coma with risk of aspiration. Historical clinical literature and contemporary reviews reiterate that high-dose exposures have led to severe, sometimes fatal, outcomes in human poisoning cases [7] [2].
5. Patterns of misuse drove many cases — single huge doses or repeated dosing
Investigators found two main patterns: ingestion of a very large single veterinary dose (for example, an entire tube of horse paste) or repeated dosing over several days. Toxicity correlates with dose and accumulation; many of the hospitalized patients had taken multiple doses or unusually large amounts compared with the single-dose regimens used for approved human indications [4] [2] [1].
6. Not every exposure causes severe harm — but side effects at recommended doses differ
When used at approved human doses for parasitic diseases, ivermectin is generally well tolerated; low‑grade side effects such as dizziness, itching or rash occur in a minority. That context appears repeatedly in reviews stressing that toxicity arises from misuse and overdosing rather than standard, prescribed regimens [8] [3].
7. Data limitations and reporting biases to keep in mind
Available sources draw on poison‑center reports, case series and historic toxicology literature; they capture severe and medically attended cases but do not quantify all milder, unreported exposures. Some reviews emphasize increases in calls during the pandemic but cannot precisely measure true incidence or long‑term outcomes in every exposed person [1] [2] [5].
8. Practical takeaway and competing perspectives
Clinicians and public-health bodies warn that veterinary ivermectin is unsafe for human use and that the active ingredient’s formulation and dose make overdose likely; published toxicology work supports this [4] [1]. Others note ivermectin’s established safety profile when used at approved human doses for specific parasitic diseases, underscoring that harm arises from inappropriate dosing or formulations — not from properly prescribed ivermectin [3] [8].
Limitations: available sources do not mention long‑term sequelae rates after recovery, nor do they provide a population‑level denominator for all people who ingested veterinary ivermectin, so precise incidence and prognosis estimates are not available in current reporting [1] [2].