CYP2C9*3 is assigned no function based on definitive evidence in homozygous and heterozygous patients and in vitro experimental data. CYP2C9*3 has been studied for more than 20 years and its association with impaired function compared to wildtype is well-established (8809086, 29283396, 20150829, 15637526). This allele was previously assigned "decreased function" but after reevaluation of prior and new evidence, CYP2C9*3 is assigned "no function" because its activity is much more decreased compared to CYP2C9*2 for multiple substrates, resulting in the lowest possible designation for the phenotypes observed in homozygous patients (12742136, 10413320, 27179628, 25775139, 19082874, 30088221). Therefore, consensus among experts was no function with an activity value of 0 based on definitive evidence.