CYP2D6 and infection: 1) First-line chloroquine–PQ treatment remains efficacious for P. vivax malaria, but > 10% of infections relapse despite routinely prescribed PQ treatment, possibly because of poor adherence and low cytochrome P450 2D6–mediated PQ metabolization. 2) Artemisinin-based combination therapies (artesunate–mefloquine and artemether–lumefantrine) remain highly efficacious for P. falciparum malaria. 3) Tafenoquine is as effective as low-dose PQ to prevent P. vivax relapses.