CYP2D6*1x≥3 is assigned increased function based on limited evidence. Subjects with CYP2D6 gene duplications demonstrated increased enzyme activity with the greatest debrisoquine metabolism among 270 subjects based on urine metabolites (7616439). Additionally, debrisoquine metabolism correlated with the number of functional CYP2D6 genes (7616439, 9012401). Therefore, consensus among experts was increased function with an activity value of ≥3 based on limited evidence as it was determined the phenotypes containing this allele would be clinically distinct from phenotypes comprising normal function alleles.