NAT2 poor metabolizers (historically referred to as “slow acetylators”) are predicted to have increased plasma hydralazine concentrations compared with NAT2 rapid and intermediate metabolizers (historically referred to as “rapid acetylators” and “intermediate acetylators,” respectively), which may lead to both increased clinical efficacy and adverse effects, including drug‐induced systemic lupus erythematosus. The gene discussed is NAT2; the disease is systemic lupus erythematosus.