Are there any documented cases of ivermectin toxicity in humans taking horse-formulated doses?
Executive summary
Reports and public-health advisories make clear that animal formulations of ivermectin are much higher-strength than human prescriptions and can be dangerous if misused; health agencies warn against using veterinary “horse paste,” and case reports of toxicity have been linked to overdosing, not to a single documented unique formulation-specific toxin [1] [2]. Manufacturers and veterinary experts note horse paste concentrations (e.g., 1.87% ≈ 18.7 mg/g) and dosing designed for 1,250–1,500 lb animals, which can deliver many times a human therapeutic dose if taken by people [3] [4].
1. Why people took horse paste: cheap, visible, and viral
During the COVID era social media and celebrity endorsements pushed people toward ivermectin; some consumers turned to horse paste because it was cheap, widely available and presented in easy syringes — despite human tablets existing and regulatory warnings [5] [6]. Journalists and medical outlets reported spikes in public interest and legislative moves to loosen access to human formulations, which partly sustained demand for alternatives such as veterinary paste [5].
2. Formulation and dose differences that matter
Veterinary ivermectin paste for horses is produced in high-concentration syringes to treat animals weighing over a thousand pounds; labels specify dose-by-weight and warn the product is not for humans (manufacturer info cites 1.87% paste and dose rates around 91 mcg per lb ≈ 200 μg/kg) [4] [3]. Human-approved ivermectin is dosed by body weight as a tablet at far lower single doses (around 150–200 μg/kg), so a single “pea-sized” serving of horse paste can contain many milligrams more than a standard human tablet [7] [4].
3. Documented harms and official warnings
Regulators and academic health centers have repeatedly warned that animal ivermectin products are different formulations and that taking large doses can be dangerous; the FDA and Cleveland Clinic both advise never using animal products on people and note lack of testing for those formulations in humans [1] [2]. Veterinary and university experts say toxicity usually results from large or repeated doses and that cumulative dosing — taking multiple doses over days — increases overdose risk [8].
4. Evidence on human toxicity cases: what sources say (and what they don’t)
Available reporting emphasizes toxic effects from overdosing on ivermectin, including cases tied to use of animal products during COVID surges, but the provided sources do not include a peer-reviewed, case-by-case registry explicitly cataloguing every human harmed by horse-formulated ivermectin; they summarize that misuse led to harmful events and emergency warnings rather than enumerating specific clinical case reports in detail [1] [2] [8]. Wikipedia and other reviews note ivermectin is relatively safe at approved human doses (~300 μg/kg cited in reviews) but point out serious adverse events can occur with high parasite loads or inappropriate dosing — not that horse paste introduces a different chemical beyond higher per-dose quantities [7].
5. Pharmacology and why overdose can happen
Human pharmacology studies show peak plasma concentrations vary by dose and formulation; higher or more readily absorbed formulations (liquid vs tablet) and repeat dosing can raise plasma levels toward ranges associated with toxicity, and horse paste bases are often “wetter” formulations that may be absorbed differently in people [9]. Reviews of human dosing trials by developers concluded tolerability up to multiples of the human-approved dose in controlled settings, but those trials do not validate unsupervised ingestion of concentrated veterinary preparations [9] [7].
6. Conflicting narratives and implicit agendas
Pro-ivermectin advocates pointed to anecdotal improvements and sought looser access to human-formulation ivermectin; some vendors and state policymakers have pushed to make human-grade ivermectin easier to obtain [5] [10]. Industry and manufacturers stress label warnings and legal prohibitions against human use of veterinary products; their messaging includes liability and market protection interests alongside safety concerns [4] [3].
7. Practical takeaway and limits of available reporting
Do not use veterinary ivermectin for people: regulators and medical centers explicitly advise against it because of unknown safety of animal formulations in humans and documented risks from large doses or cumulative use [1] [2]. The sources provided do not deliver a named, comprehensive list of individual human poisoning case reports tied exclusively to horse-formulated ivermectin; they offer institutional warnings, pharmacology context, and manufacturer labeling that together document the risk pathway [8] [4].