Which documented clinical adverse events have been linked specifically to inactive ingredients in veterinary ivermectin exposures?

1. What the reports actually document: clinical harms after veterinary-product exposures

Poison control centers, public‑health agencies and case series report that patients who ingested veterinary ivermectin formulations experienced neurotoxicity (confusion, decreased consciousness, ataxia), gastrointestinal symptoms (nausea, vomiting, diarrhea), musculoskeletal complaints, hypotension, seizures, coma and in some cases death — findings summarized in a retrospective Oregon Poison Center analysis and multiple health‑agency advisories ^{[1] [4] [5] [6]}.

2. What regulators say about inactive ingredients — strong caution, not proven causation

U.S. regulators and health organizations repeatedly warn that veterinary products often contain inactive ingredients not evaluated for human use and that the effects of those components on drug absorption or on human safety are unknown; these statements are cautionary rather than causal: the FDA and media summaries note uncertainty about how excipients might change ivermectin’s potency or safety in humans ^{[2] [3]}.

3. Where the evidence is firm — formulation, dose and route drive documented harms

The peer‑reviewed case literature and clinical reports emphasize excessive dose, inappropriate formulation (high‑concentration pour‑on, injectable or drench products), and non‑oral routes (notably intravenous use) as proximate causes of severe toxicity — for example, a reported neurotoxicity case after intravenous administration of a veterinary formulation highlights route as a key factor in the observed harm ^{[7] [1] [8]}.

4. The gap in attribution: no sourced report that pins a specific adverse effect solely on an inactive ingredient

Across the reviewed public‑health advisories, poison‑center analyses and product labels there is no documented clinical case that isolates an inactive ingredient in veterinary ivermectin as the definitive cause of a particular adverse event; rather, authors and agencies consistently state that inactive ingredients “have not been evaluated for use in humans” and “could” affect absorption or safety, leaving attribution unresolved in the available record ^{[2] [4] [3]}.

5. Plausible mechanisms and alternative explanations acknowledged by sources

Authorities and clinicians outline plausible ways excipients might matter — by altering oral bioavailability, causing allergic or irritant reactions, or enabling formulations intended for topical or large‑animal use to deliver much higher systemic doses — but they pair those hypotheses with the more concrete explanations supported by data: overdose, pharmacologic neurotoxicity of ivermectin, and misuse of intravenous or concentrated veterinary products ^{[3] [1] [7]}.

6. Reporting nuances, implicit agendas and what that means for interpretation

Public advisories from regulatory and tribal health entities aim to curb misuse and prevent shortages for animals, an implicit public‑health and veterinary‑supply protection goal that may emphasize worst‑case harms and uncertainty about excipients; nevertheless, the underlying case data cited focus on clinical syndromes consistent with ivermectin toxicity from excessive systemic exposure rather than documented excipient reactions ^{[2] [5] [9]}.

7. Bottom line and limits of the public record

Documented clinical adverse events after human exposure to veterinary ivermectin include neurotoxicity, gastrointestinal symptoms, hypotension, seizures, coma and death, but the sources reviewed do not provide documented cases that attribute specific clinical events directly and solely to inactive ingredients in those products — the regulators’ warnings are principled cautions about unknown risks rather than evidence linking particular excipients to particular harms ^{[1] [6] [3]}.