CYP2C9*23 is assigned decreased function based on limited evidence. Multiple in vitro studies found CYP2C9*23 demonstrated decreased clearance compared to wildtype (23844998, 24118918, 25144335, 25476996, 23752738, 25832633, 25884291, 25924705, 24077631). Although three in vitro studies showed CYP2C9*23 had similar activity compared to wildtype, the experts did not find these results convincing as in these studies CYP2C9*2 which definitively has decreased function, demonstrated increased or similar activity compared to wildtype in these studies (25142737, 25951663, 27163851). 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.