synthetic drug used in the treatment of malaria, an infection caused by the protozoan parasite Plasmodium transmitted to humans by the bite of various species of Anopheles mosquitoes. Introduced into medicine in the 1950s, primaquine is one of an important series of chemically related antimalarial agents, the quinoline derivatives. It is administered orally as primaquine phosphate.

Primaquine inhibits the development of the malarial parasites Plasmodium vivax and P. ovale in both blood and tissue, thus curing the disease and preventing relapses. Some abdominal discomfort may occur as a side effect.