What are the clinical risks and documented adverse events from human ingestion of animal ivermectin or phenylbutazone products?
Executive summary
Animal formulations of ivermectin have been repeatedly linked to gastrointestinal symptoms, rapid-onset neurotoxicity (including confusion, loss of coordination, seizures, coma) and at least one reported death in clinical series; veterinary products’ higher concentrations and untested inactive ingredients magnify those risks and can interact with other drugs, prompting FDA warnings against human use [1] [2] [3] [4]. Evidence about phenylbutazone from the supplied reporting is limited to veterinary pharmacokinetic studies showing placental and lactational transfer in cows, not to documented human overdoses in these sources, so direct clinical risk data in people are not present in the provided materials [5] [6].
1. Ivermectin overdoses produce a predictable clinical syndrome centered on the gut and brain
Multiple federal and clinical sources catalog the common adverse effects after ingestion of veterinary ivermectin: nausea, vomiting, diarrhea, hypotension, pruritus and hives, dizziness, visual disturbance, loss of balance, altered mental status and seizures, with progression in severe cases to coma and death; the Indian Health Service and FDA list this combination of GI and neurologic signs as characteristic of toxicity [1] [4].
2. Case series and reports document real-world harm from veterinary formulations
A comparative clinical series identified 37 cases of ivermectin toxicity with a median age of 64, most requiring emergency or inpatient care; patients who consumed veterinary formulations typically ingested large single doses or repeated large daily doses and developed rapid-onset neurotoxicity, and the series reported one death among the cohort [2]. A separate case report describes intravenous administration of a veterinary ivermectin preparation to a COVID-19 patient that produced severe neurotoxicity, underscoring the danger of non-oral, non-approved routes and formulations [7].
3. Why animal products are riskier than human prescriptions
The active molecule may be identical across formulations, but animal products often contain much higher concentrations intended for horses or cattle and include inactive ingredients and vehicles not evaluated for human safety; those differences can alter absorption and potency and raise toxicity risk when people ingest them [1] [8] [9]. Regulators explicitly warn that veterinary formulations are not substitutes for human prescriptions and ask the public to report misuse and fraudulent claims [3].
4. Drug interactions and vulnerable populations amplify danger
Ivermectin can potentiate central nervous system depression and increase sedative effects of benzodiazepines and barbiturates, and approved human formulations also carry interaction warnings with drugs such as blood thinners—factors that make uncontrolled dosing with veterinary products particularly hazardous, especially in older adults and those on concomitant medications [4] [1]. Poison control centers and clinicians noted spikes in exposures during the COVID-19 period tied to attempts at self-treatment, reflecting real-world harms from self-medication with animal-grade products [8] [10].
5. Phenylbutazone: veterinary transfer documented, human adverse-event data lacking in this reporting
The supplied literature on phenylbutazone pertains to animal pharmacokinetics: studies in Holstein cows show phenylbutazone crosses the placenta and appears in calf plasma at birth at about half the dam’s steady-state level, and accumulates via lactation—demonstrating biologic transfer in that model but not providing clinical human toxicity case data in these sources [5] [6]. Because the provided sources do not report human ingestion events for phenylbutazone, conclusions about human clinical risks must be limited to recognizing potential exposure routes rather than documented adverse-event profiles.
6. What the reporting allows clinicians and the public to conclude
The evidence in the supplied reporting supports three firm conclusions: animal ivermectin ingestion has caused significant GI and neurologic toxicity in humans, including hospitalizations and at least one death [2] [4]; veterinary formulations are intrinsically riskier than human-approved products because of dose and excipient differences [1] [8]; and regulators (FDA, IHS) explicitly advise against human use of animal ivermectin and urge reporting of such products [3] [4]. The supplied material does not provide human-case adverse-event data for phenylbutazone, only animal-transfer pharmacokinetics that indicate potential exposure routes [5] [6].