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Are there case reports of ivermectin poisoning from horse dewormer in 2020–2024?
Executive Summary
There are multiple documented case reports and surveillance data showing ivermectin poisoning linked to veterinary products (including horse/cow formulations) during 2020–2024, driven largely by misuse related to COVID‑19. Poison control center call spikes in 2021, focused clinical series from 2021–2022, and public‑health advisories document overdoses after ingestion or unconventional administration of highly concentrated veterinary ivermectin; rare fatal and severe cases have been reported, including later published fatal transdermal poisoning accounts. These signals come from poison center surveillance, a regional clinical toxicology series, and national public‑health advisories that collectively validate the existence of case reports and increased harms in the 2020–2024 window [1] [2] [3] [4] [5].
1. Sudden surge in poison‑center calls that first flagged the problem
U.S. poison control centers recorded a dramatic uptick in ivermectin exposure calls beginning in mid‑2021, with a 245% increase in July–August 2021 compared with the prior period and 1,143 exposures reported from January–August 2021 — signals explicitly tied to use of veterinary formulations intended for large animals. Public‑health surveillance from the National Poison Data System and contemporaneous media and advisory reports show most overdoses involved products formulated for cows and horses and coincided with widespread public speculation about ivermectin for COVID‑19. The Centers for Disease Control and other toxicology organizations issued warnings as clinicians saw three‑fold increases in exposure calls and cases of severe toxicity that required medical care [1] [3] [6].
2. Clinical series document veterinary‑product overdoses and worse outcomes
A focused clinical toxicology series from the Oregon Poison Center during late 2021–early 2022 identified 37 cases of ivermectin toxicity, with 17 involving veterinary formulations and 15 involving human prescription tablets; those consuming veterinary products took higher doses and had higher rates of altered mental status. The study demonstrates that overdoses on veterinary formulations were not only more frequent in some settings but also associated with more severe neurologic presentations. The case mix included acute ingestions and chronic misuse, reinforcing that both single high‑dose misuse and repeated excess dosing produce clinically relevant toxicity [2].
3. Public‑health advisories and medical toxicology reports framed the risk
Federal and specialty bodies issued advisories in 2021 warning that ivermectin is not authorized for COVID‑19 and that veterinary formulations pose particular dangers when used by humans. The CDC and American College of Medical Toxicology summarized surveillance showing rising prescriptions, increased poison‑center activity, and cases with symptoms ranging from gastrointestinal upset to coma and seizures. These advisories emphasized that the risk period began in 2021 but built on isolated misuse in 2020, and they urged clinicians and the public to avoid veterinary ivermectin for human use and to seek care for suspect exposures [3] [7].
4. Fatal and severe case reports expanded the clinical picture in later publications
Individual case reports published after the initial 2021 surge documented severe and fatal outcomes, including a reported death from transdermal ivermectin poisoning with a recorded plasma concentration of 27 ng/mL and diffuse cerebral edema. While some fatal reports were published in 2025, they describe exposures and misuse patterns that began during the COVID‑19 era and underscore that unconventional routes (transdermal application) and prolonged excessive dosing can produce catastrophic neurologic injury. These case reports complement surveillance series by providing pathophysiologic detail and treatment attempts, and they highlight there is no specific antidote; care is primarily supportive and focused on toxin elimination [4] [5].
5. What the evidence supports and what remains uncertain
The combined data set — poison‑center surveillance spikes in 2021, regional clinical series from 2021–2022, toxicology society reports, and later fatal case narratives — confirms that case reports and documented poisonings from veterinary ivermectin (including products for horses/cattle) occurred during 2020–2024. Surveillance most strongly documents 2021 as the inflection year; clinical series cover 2021–2022, and later individual fatal case publications elaborate on mechanisms and outcomes. Uncertainties remain about precise national counts across 2020–2024, long‑term outcomes for nonfatal cases, and whether some severe cases attributed to veterinary versus human formulations reflect formulation differences, dose differences, or co‑ingestants — issues requiring continued toxicovigilance and systematic reporting [1] [2] [8].
6. Why multiple perspectives matter and policy implications
Public‑health agencies, poison centers, and clinicians framed the problem as misuse driven by misinformation about COVID‑19 treatments, while case‑series authors and case reporters documented clinical consequences and attempted interventions. The convergence of surveillance and case reports supported advisories discouraging off‑label use of veterinary ivermectin and spurred education for clinicians and the public. The evidence supports continuing monitoring, clearer labeling and distribution controls for veterinary products, and improved clinician awareness that veterinary ivermectin exposures can cause serious neurologic and systemic toxicity necessitating emergency care [3] [7] [2].