Using a combined analysis based on the mutant alleles of both CYP2C9 and CYP2C19 genes, Tan et al. categorized patients of epilepsy into three groups, including (1) extensive metabolizers (EM) with the wild-type genotypes of the homozygous combination of CYP2C9*1*1 and CYP2C19*1*1, (2) intermediate metabolizers (IM) with the heterozygous combinations of two out three genotypes (CYP2C9*1*3, CYP2C19*1*2, or CYP2C19*1*3), and (3) poor metabolizers (PM) with genotypes of mutant homozygous combination of either CYP2C9*3*3, CYP2C9*1*3, or CYP2C19*2*2 [50]. The gene discussed is CYP2C9; the disease is epilepsy.