CYP2D6*10x2 is assigned decreased function based on limited evidence. Three subjects with CYP2D6*10/*10x2 genotype demonstrated similar dextromethorphan metabolism compared to CYP2D6*10/*10 subjects and decreased metabolism compared to CYP2D6 *1/*1, CYP2D6 *1/*2, and CYP2D6*1/*10 subjects based on urine metabolites (15149890). Therefore, consensus among experts was decreased function with an activity value of 0.5 based on limited evidence as it was determined the phenotypes containing this allele would be clinically distinct from phenotypes comprising normal function alleles and clinically similar to phenotypes comprising decreased function alleles.