What are the risks and side effects of using veterinary ivermectin in humans?
Executive summary
Using veterinary ivermectin products in humans can cause overdose and serious toxicity; reported ingested veterinary doses ranged from about 6.8 mg up to 125 mg of paste and 20–50 mg of liquid, and case series linked such use to hospitalizations and neurologic toxicity [1]. Human-prescribed ivermectin has approved indications and weight‑based dosing (about 200 mcg/kg) with generally uncommon side effects, whereas veterinary formulations are concentrated and not evaluated for human safety [2] [3] [4].
1. Why people take veterinary ivermectin — and why that matters
Some people turned to veterinary ivermectin during the COVID‑19 pandemic despite no high‑quality evidence that it prevents or treats COVID‑19; randomized trials show no clinical benefit for COVID‑19 and public attention drove increased human prescriptions and veterinary product use [1]. Veterinary products are formulated and concentrated for large animals and so can deliver far higher doses per administration than the human tablet approved for parasitic infections, creating a clear overdose risk [3] [4].
2. Typical approved human dosing and expected side effects
When prescribed for parasitic infections, ivermectin dosing is weight‑based (commonly 200 micrograms per kilogram as a single dose) and tablets come in small strengths (for example, 3 mg each); in these regulated uses side effects are usually uncommon and often mild (gastrointestinal upset, rash, transient dizziness) [2] [5]. Drug information resources list nervous‑system effects such as dizziness, headache, somnolence, vertigo and tremor among reported adverse reactions to human‑formulation ivermectin [6].
3. Reported harms from veterinary formulations and overdoses
Clinical reports and poison‑center analyses document people ingesting veterinary paste or liquid—reported ranges included 6.8 mg to 125 mg of 1.87% paste and 20–50 mg of 1% solution—with six of 21 patients in one NEJM case series hospitalized for toxic effects; many reported taking the drug for COVID‑19 prevention [1]. A larger review of poison‑center and clinical data found toxicity typically in older males who took higher‑than‑recommended doses and presented mainly with neurologic symptoms plus gastrointestinal and musculoskeletal complaints [7].
4. The primary danger: neurologic toxicity and why it can happen
Ivermectin normally has poor penetration into the human brain because P‑glycoprotein (mdr‑1) pumps limit its access; however, high doses, genetic differences in transport proteins, or coexisting conditions (and very high microfilarial loads in certain parasitic infections) can allow central nervous system accumulation and produce encephalopathy, confusion, stupor, seizures or coma—effects documented in both human treatment campaigns and individual toxicities [8] [6]. Case reports and reviews repeatedly link neurological events to overdose or special circumstances [8] [6].
5. Other at‑risk groups and special cautions
Children under 15 kg and pregnant people are groups with limited safety data; pediatric use is cautioned because the developing blood‑brain barrier could increase CNS risk, and the effects in pregnancy are not well established [5] [9]. Public‑health agencies explicitly warn against using animal drugs in people because those products were not evaluated for human safety and dosing [4].
6. What the sources say about long‑term or rare outcomes
Serious or fatal encephalopathy is rare but has been reported, particularly in contexts of heavy Loa loa infection or overdose, and neurological events have been a central concern in large ivermectin campaigns and in overdose case series [8] [6]. Available sources document hospitalizations and severe neurologic presentations after veterinary‑product ingestion; they do not provide a comprehensive, long‑term cohort study of chronic outcomes from such misuse [1] [7].
7. Competing perspectives and limitations of the record
Clinical and toxicology reports agree: human‑formulation ivermectin has accepted parasitic indications and known side effects while veterinary products pose overdose risk [2] [3] [4]. Some advocacy for off‑label use during the pandemic occurred despite randomized trials showing no COVID‑19 benefit [1]. Available sources do not mention detailed incidence rates of adverse events across the general population who self‑medicate with veterinary ivermectin, nor long‑term follow‑up after severe toxicity (not found in current reporting) [1] [7].
8. Practical takeaways and reporting cues
Do not take veterinary ivermectin intended for animals; regulators and clinical reviews explicitly warn against it because concentration, excipients and dosing differ and have caused hospitalizations [4] [3] [1]. If exposure or overdose is suspected, seek urgent medical care—reported toxic presentations are primarily neurologic and may require hospitalization [1] [7]. For approved indications ask a clinician about weight‑based dosing and expected side effects for human formulations [2].
Limitations: this summary relies on clinical case series, poison‑center reports and drug information summaries provided above; population‑level risks and long‑term outcomes after veterinary ivermectin misuse are not comprehensively described in the cited sources (not found in current reporting) [1] [7].