Fact check: What ivermectin doses have caused toxicity in humans and what were the typical symptoms and outcomes (with dates/years of reported cases)?

1. What the records claim about who overdosed, how much, and when — a stitches-together narrative

Reports from 2021 captured an early spike in ivermectin exposures tied to COVID-19 misinformation, with poison center calls and health advisories documenting substantial increases in overdoses, especially from people using veterinary products intended for animals rather than human formulations. The New Mexico and Texas health advisories in August–September 2021 described clusters of patients presenting with gastrointestinal symptoms, hypotension, altered mental status, and seizures after ingesting excess doses; state poison centers reported call volumes rising by over 150% in some jurisdictions ^{[1] [2]}. Peer-reviewed and observational studies that followed tracked similar patterns into 2022 and 2025, noting that cases continued to be driven by either acute ingestion of large veterinary doses or chronic overuse of human tablets for prevention or treatment of COVID-19 ^[3].

2. Doses associated with toxicity — what the data say about amounts and regimens

Case series and clinical analyses identify two clear exposure patterns: acute very-high-dose ingestion (often veterinary formulations) and repeated supratherapeutic dosing of human formulations over days to weeks. A multi-case analysis reported patients taking chronic human-formulation ivermectin at a median daily dose of about 13.5 mg for a median of 3.8 weeks who developed milder but persistent symptoms, while those exposed to veterinary products generally received far higher absolute doses and experienced more severe neurotoxicity ^[3]. Early 2021 surveillance and case reports did not always quantify exact milligram amounts for each patient, but described clinical severity correlating with known substantial overdoses or inappropriate dosing intervals ^{[1] [5]}.

3. Typical symptoms and clinical course — a consistent clinical fingerprint

Across health-advisory reports and clinical series, gastrointestinal complaints (nausea, vomiting, diarrhea), central nervous system effects (dizziness, confusion, ataxia, decreased consciousness), hypotension, and seizures recur as dominant manifestations. Most surveillance data from 2021–2022 described patients who were symptomatic enough to seek care; several were hospitalized but survived with supportive care, while a minority experienced severe neurologic injury or prolonged recovery ^{[1] [2] [5]}. The 2022 case series reinforced that veterinary-formulation exposures more often produced altered mental status and more severe neurotoxicity compared with chronic human-formulation misuse, which tended to produce less dramatic but still clinically meaningful symptoms ^[3].

4. Rare severe outcomes, including fatalities — documented exceptions and dates

Fatal outcomes have been rare but documented. A 2025 case report described a fatal transdermal ivermectin poisoning associated with a plasma concentration of 27 ng/mL, progressive cerebral edema, and intracranial hypertension despite treatment, underscoring that routes other than oral ingestion and very high exposures can be lethal ^[4]. Earlier 2021 surveillance letters and series reported no deaths in some cohorts but did report multiple hospitalizations and intensive care admissions for seizure or profound encephalopathy; these data show that while most overdoses are survivable with supportive care, severe neurologic injury and death can occur under particular high-dose or atypical-exposure circumstances ^{[5] [1]}.

5. Veterinary vs. human formulations — why formulation matters for risk

Analyses repeatedly separate cases by formulation, noting that veterinary ivermectin products contain higher concentrations, different excipients, and packaging that leads to misdosing, and they are strongly associated with more severe neurotoxicity when ingested. Human-tablet chronic misuse produced a distinct pattern of prolonged, lower-grade toxicity in some patients, such as persistent GI upset and neurocognitive symptoms after weeks of overuse; the 2022 multi-case review explicitly links formulation to outcome severity ^[3]. Public health advisories emphasized that the accessibility and labeling of veterinary products created particular risk during the 2021 misinformation waves, prompting poison control and health department alerts ^{[2] [1]}.

6. What the evidence leaves out and where interpretations diverge — limits and implications

Available reports vary in completeness: many public health advisories and letters provide symptom descriptions and exposure context but lack precise mg/kg dosing for each patient, making dose–response quantification imperfect. Case series provide more dosing detail but may be biased toward patients who sought medical care, and isolated case reports highlight extreme outcomes that are rare but dramatic ^{[3] [4]}. The literature consistently supports that overdoses above therapeutic regimens cause predictable GI and neurologic toxicity and that veterinary product ingestion or exceptionally high/atypical exposures carry the greatest risk; however, exact threshold doses for severe outcomes remain heterogeneous across cases and depend on route, body weight, co-ingestions, and healthcare access ^{[1] [5]}.