What specific excipients in veterinary ivermectin products are known to be harmful to humans?
Executive summary
Veterinary ivermectin products can contain inactive ingredients and secondary drugs that are untested for human use; the published literature specifically flags clorsulon as a secondary active ingredient present in some veterinary mixes and therefore a potential source of harm if consumed by humans [1]. Regulatory and clinical reporting emphasizes that most human harm reported after ingesting veterinary ivermectin stems from high ivermectin doses, inappropriate routes (injectable/parenteral) and uncharacterized excipients or solvents rather than a well-documented roster of named, universally hazardous additives [2] [3] [4].
1. What the question really asks and what the evidence can answer
The user seeks concrete names of excipients in veterinary ivermectin that are demonstrably harmful to humans; the available reporting does not provide a comprehensive public inventory of hazardous excipients in every veterinary product, but it does identify at least one named compound—clorsulon—reported as a secondary active in some veterinary formulations and flagged as an untested substance with unknown human health impacts [1], while regulators and clinical reviews stress that many veterinary formulations include solvents, preservatives, carriers or secondary actives that have not been evaluated for human safety [2] [5].
2. The one specific compound that appears in the published analyses: clorsulon
A recent analytical study of veterinary ivermectin products consumed off‑label identified clorsulon as a secondary active present in some formulations and explicitly warned that such secondary actives “can cause unknown (long‑term) health impacts in humans,” making clorsulon the clearest named excipient/secondary agent of concern in the scientific record reviewed here [1].
3. Why most harm reported is attributed to dose, route and uncharacterized excipients, not a fixed short list of toxins
Multiple official and clinical sources emphasize that veterinary products are often concentrated, formulated for parenteral or topical animal use, and include solvents, carriers and preservatives tailored to animals; FDA and veterinary medicine experts warn that the dose, delivery form and untested additives—not a small set of universally dangerous excipients—are the main drivers of the adverse events seen when people ingest veterinary ivermectin [2] [4] [6]. Case reports of severe neurotoxicity after intravenous administration of veterinary ivermectin illustrate harm from an improper route and high systemic exposure rather than a named preservative [3], and toxicology reviews link most clinical manifestations to ivermectin overdose itself while noting increased poison‑center calls tied to veterinary formulations [7] [8].
4. What is not known and where reporting is limited
The public sources examined do not provide an exhaustive, public list of all excipients across manufacturers of veterinary ivermectin nor do they document dose‑response harms in humans for specific common veterinary excipients other than flagging clorsulon as a concern; therefore it is not possible from the cited reporting to state that other named excipients (for example certain solvents, preservatives or dyes) are definitively harmful to humans without product‑specific analysis and toxicology data [1] [5].
5. Practical implications and recommended next steps based on the evidence
Regulatory guidance and clinical literature consistently recommend against using veterinary ivermectin in humans because the products are formulated for animals, can be highly concentrated, may contain secondary actives or excipients untested in people, and can be administered by routes inappropriate for humans—facts documented by the FDA and peer‑reviewed analyses [2] [1] [3]; resolving which excipients are harmful in a given product requires inspecting the product label and, when labels list secondary actives (e.g., clorsulon), consulting toxicology data or poison‑control experts since blanket assertions beyond those documented would exceed available reporting [1] [2].