What are the typical therapeutic doses of ivermectin for approved human uses and how do they compare to doses that cause toxicity?
This fact-check may be outdated. Consider refreshing it to get the most current information.
Executive summary
Typical, approved human ivermectin doses are in the range of 0.15–0.20 mg/kg as single oral doses for parasitic infections (for example, 150 µg/kg for onchocerciasis and 200 µg/kg for many indications), with tablet strengths often given as 3 mg and dosing based on weight [1] [2] [3]. Toxicity in humans is uncommon at those doses; animal LD50s and human case reports show neurologic and systemic toxicity at much higher exposures (multiple mg/kg to tens of mg/kg, or with repeated misuse or veterinary formulations), though measured toxic thresholds vary by species and by blood‑brain barrier/P‑glycoprotein function [4] [5] [6] [7] [8].
1. What regulators approve and what doses they endorse
Major prescribing references and health centers list ivermectin as an approved antiparasitic with human oral regimens dosed by weight: standard single‑dose regimens include about 0.15 mg/kg for onchocerciasis and about 0.20 mg/kg for strongyloidiasis and other uses; tablets are typically 3 mg and clinicians calculate a one‑time dose by body weight [1] [2] [3]. Topical formulations for lice and rosacea are approved separately [9] [10].
2. How typical therapeutic doses compare to experimentally measured lethality
Preclinical LD50 data differ by species: oral LD50 values reported in mice and dogs translate to very large mg/kg ranges compared with human therapeutic mg/kg: Wikipedia cites mouse LD50 ~25 mg/kg and dog LD50 ~80 mg/kg, giving an approximate human‑equivalent LD50 range of roughly 2–43 mg/kg—far above the 0.15–0.20 mg/kg therapeutic window [4]. Human poisoning reports typically involve doses far above therapeutic levels (for example, repeated 21 mg tablets twice weekly or veterinary product ingestion) and have led to hospitalizations [6].
3. What “high dose” human safety data show
Clinical and trial literature indicates researchers have administered and studied higher-than-standard doses for purposes like malaria transmission reduction; some trials and reviews report tolerability up to several hundred to 2,000 µg/kg (i.e., 0.8–2.0 mg/kg) under monitoring, and meta-analyses say usual doses (0.2–0.4 mg/kg) are considered extremely safe [11] [12]. Yet “higher” in trial settings still remains well below animal LD50 estimates and is supervised, not a blanket endorsement for unsupervised self‑medication [11] [12].
4. Where and how toxicity occurs — mechanisms and risk factors
Toxic effects reported in humans center on neurologic signs (confusion, ataxia, seizures, coma), gastrointestinal symptoms, and liver or metabolic issues in some settings; severe cases have been linked to high cumulative or repeated dosing and to use of veterinary products with unintended concentrations or excipients [13] [6] [9]. Genetic or physiologic impairments of P‑glycoprotein (MDR1/ABCB1) increase brain penetration of ivermectin and dramatically raise sensitivity in animal models — a mechanism that plausibly explains human susceptibility variation [8].
5. Practical thresholds cited by clinicians and poison centers
Emergency and prehospital guidance notes limited human overdose data but points to animal models where toxicity appeared between about 5–15 mg/kg; some poison‑control guidance recommends hospital evaluation for ingestions exceeding ~2 mg/kg because of potential central‑nervous‑system effects [7]. Case series from the COVID‑era document hospitalizations after non‑standard regimens — e.g., 21 mg tablets taken twice weekly — and veterinary product ingestion with higher milligram exposures [6] [9].
6. Why public discourse sometimes confuses dose and safety
Public debate around repurposing (for COVID‑19 or cancer) mixed in vitro antiviral concentrations with achievable human plasma levels; critics note the concentrations that inhibited SARS‑CoV‑2 in petri dishes would require doses many times higher than approved human doses and approach toxic ranges in animals, a key reason regulators did not approve ivermectin for COVID‑19 [4] [10]. Meanwhile, legislative changes in some U.S. states expanding access to ivermectin have increased availability without changing clinical dosing guidance, raising concerns among clinicians about unsupervised high‑dose use [14] [15].
7. Bottom line for clinicians and the public
Approved human dosing is weight‑based and low (0.15–0.20 mg/kg single doses) and is safe when used for labeled parasitic indications [1] [2] [3]. Toxicity emerges at much higher exposures, with case reports and animal data showing neurologic and systemic harm when people take multiple milligrams per kilogram or veterinary formulations; individual susceptibility varies and can be amplified by P‑glycoprotein dysfunction or drug interactions [6] [5] [8]. Available sources do not mention an authoritative single human LD50; human risk assessment relies on animal toxicology, clinical trials of higher doses, and poisoning case series [4] [11] [7].