What are risks and symptoms of ivermectin overdose in humans after taking veterinary formulations?

1. What investigators actually claimed — a concise extraction of the evidence that matters

Clinical case series and poison‑center reports converge on a small set of repeatable claims: people who ingest veterinary ivermectin tend to take higher doses and develop more frequent and more severe neurotoxic effects than those taking prescription human tablets, and many affected patients are older men using the drug for COVID‑19 prevention or treatment. Case counts reported include 37 patients analyzed in a Clinical Toxicology series with 17 exposures to veterinary products; investigators documented higher rates of altered mental status, hospitalization, and at least one death in the aggregated dataset ^{[2] [3]}. These reports stress that veterinary products are often more concentrated and can contain toxic inactive ingredients, increasing overdose risk ^[4].

2. The symptom picture you are most likely to see — from mild complaints to life‑threatening neurologic collapse

Across the reports the symptom profile is consistent: gastrointestinal symptoms (nausea, vomiting, abdominal pain), musculoskeletal complaints, and a predominance of neurologic effects including dizziness, ataxia, confusion, weakness, decreased consciousness, seizures, and in severe cases respiratory failure or coma. Onset is often rapid after a large, single ingestion — many patients developed symptoms within two hours — and neurotoxicity was the most commonly reported clinical effect in the case series ^{[1] [5]}. Several articles note that milder, chronic exposures can produce less dramatic symptomatology, but acute high‑dose ingestions drive the most severe presentations and resource‑intensive care, including ICU admissions ^[3].

3. Who is at higher risk and why the veterinary products stand out

Reports identify older adults, particularly men over age 60, as the most frequently affected demographic, often self‑medicating to prevent or treat COVID‑19. Veterinary formulations stand out because they are higher concentration, packaged for large animals, and may contain non‑pharmaceutical excipients that elevate toxicity risk; patients using those products typically ingested substantially larger milligram doses than would be prescribed for humans ^{[2] [4] [3]}. The case series also documents that single, large first‑time doses produced rapid severe symptoms, whereas chronic smaller dosing patterns tended to produce milder but still clinically relevant toxicity ^{[5] [3]}.

4. How frequently this has been observed and the clinical burden on health systems

Poison‑center call volume and published case series document a notable spike in exposures. The New England Journal of Medicine report cited a rapid increase in calls to the Oregon Poison Center in August 2021, with many callers having purchased veterinary ivermectin; six of 21 reported patients required hospitalization and four needed ICU care in that sample, although no deaths occurred in that particular cohort ^[1]. The Clinical Toxicology compilation tallied 37 cases across study periods with multiple hospitalizations and one reported death in the aggregated dataset, indicating measurable clinical burden and occasional fatal outcomes when high doses are taken ^{[2] [3]}.

5. Timing, dose patterns, and clinical course — what clinicians observed in practice

Investigators consistently report that large single ingestions cause symptoms within hours, primarily neurologic and gastrointestinal, while chronic ingestion at lower doses tends to evolve more slowly and produce milder presentations. Reported ingested amounts varied widely: paste and solution veterinary products yielded milligram doses far above human therapeutic regimens, and symptom severity correlated with higher total ingested dose in multiple case reports ^{[1] [5]}. Clinical management described in these reports relied on supportive care and standard toxicology protocols; some cases required ICU support for seizures or respiratory compromise ^{[3] [1]}.

6. Conflicting messages, public‑health implications, and who is pushing which narrative

The sources reveal tension between clinical toxicology evidence and public messaging: poison centers and clinicians emphasize documented harms and rising exposures tied to misinformation about COVID‑19 treatments, while public advocacy for ivermectin (outside of authorized indications) may downplay risks. Regulatory and public‑health advisories cited here uniformly warn against using veterinary products in humans and note that ivermectin is not approved by the FDA for COVID‑19 — warnings that correspond with the observed case clusters ^{[1] [6]}. These patterns indicate a clear public‑health imperative: avoid veterinary formulations, follow medical guidance, and seek immediate medical attention or call poison control if symptomatic after ingestion ^{[4] [1]}.