Vivax malaria relapse following PQ treatment has predominantly been observed in patients carrying decreased function alleles such as CYP2D6*10, *36, and *41, and nonfunctional alleles such as CYP2D6*4 and *5 in various combinations giving rise to IM and PM phenotypes (Bennett et al., 2013; Ingram et al., 2014; Baird et al., 2018; Dijanic et al., 2018; He et al., 2019; Martin Ramirez et al., 2020; Mat Salleh et al., 2020; Silvino et al., 2020). The gene discussed is CYP2D6; the disease is malaria.