A Nobel-winning parasite drug started out protecting dogs from heartworm
Ivermectin was discovered in 1975 and first used by vets against heartworm and mites. Approved for people in 1987, it became a weapon against river blindness and other parasitic diseases, earning William Campbell and Satoshi Ōmura the 2015 Nobel Prize. It works by paralysing parasites' nerves and muscles, and it has no proven role against COVID-19.
Part of the avermectin family, ivermectin can be swallowed or applied to skin. It treats roundworm infections and a range of external parasites, including head lice, scabies, strongyloidiasis, whipworm and lymphatic filariasis. It appears on the World Health Organization's essential medicines list, is sold as a generic, and in 2023 ranked 295th among American prescriptions with more than 400,000 filled.
Its largest impact comes through mass drug administration, where whole communities affected by river blindness or lymphatic filariasis receive doses. Because adult worms live in the skin for 10 to 15 years and keep releasing larvae, the drug is given at least yearly across that lifespan. The WHO calls it the drug of choice for strongyloidiasis. Paired with albendazole, the two act together: ivermectin paralyses, albendazole starves the worm of energy. In January 2025 a committee of the European Medicines Agency backed a fixed combination for soil-transmitted worm infections in people aged five and over.
For scabies, a mite infestation, it is usually given twice: the first dose kills active mites but not their eggs, so a second a week later catches the hatchlings. That regimen matches a single application of permethrin cream, and ivermectin does better in mass treatment where scabies is endemic. Severe crusted scabies may call for up to seven doses in a month. It is also used for rosacea and blepharitis.
At standard doses of around 300 micrograms per kilogram it is considered relatively non-toxic, with fever, itching and rash the uncommon side effects. Serious reactions are likelier in people carrying huge numbers of Loa loa larvae, above 30,000 per millilitre of blood, and large overdoses can depress the nervous system. Data on children under five or 15 kilograms are limited. During the pandemic, claims spread that it prevented or cured COVID-19; the FDA, CDC, EMA and WHO all advised against using it that way, and later rumours about hantavirus lacked support too.
Source: Ivermectin
