When used in patients with the Viangchan variant, which confers moderately severe G6PD deficiency, PQ0.75 caused a 4-fold higher absolute decrease (P = .0002) in the median Hb level between baseline and day 7, compared with P. vivax–infected G6PD normal (G6PD+) patients (−2.2 g/dL [interquartile range {IQR}, −4.9‒0.8 g/dL] vs −0.5 g/dL [IQR, −2.2‒2.8 g/dL]). The gene discussed is GSTM1; the disease is G6PD deficiency.