CYP2C9*10 is assigned uncertain function based on conflicting in vitro data and no clinical data. Although CYP2C9*10 demonstrated decreased warfarin clearance (23752738) it also demonstrated similar activity with a tolbutamide substrate (15284535) and activity ranging from decreased to normal with 7-ethoxycoumarin, flavanone, and steroid substrates (28758225) compared to wildtype. Therefore, consensus among experts was not achieved and uncertain function was assigned.