CYP2C9*5 is assigned decreased function based on strong evidence in heterozygous patients and in vitro studies. Three subjects carrying the CYP2C9*5 allele (CYP2C9*1/*5, CYP2C9*5/*6, CYP2C9*5/*8 genotype) had decreased losartan metabolism compared to wildtype based on urinary metabolites after a single 25mg dose (15289788). Two CYP2C9 *1/*5 subjects, one CYP2C9 *5/*6 subject, and one CYP2C9*5/*8 subject had lower phenytoin metabolism compared to wildtype based on urinary excretion of a phenytoin metabolite after a single 300mg dose. Additionally, the CYP2C9 *5/*6 subject demonstrated the lowest phenytoin metabolism as the only subject of the 109 subject cohort to have a urinary metabolite concentration below the limit of quantification (16220110). One CYP2C9 *5/*8 demonstrated the lowest acenocoumarol metabolism based on plasma concentrations in a 36 subject cohort (21811894). One CYP2C9*1/*5 subject demonstrated decreased indisulam metabolism with an AUC nearly two times greater than wildtype subjects (17504998). These results correlated with in vitro pharmacokinetic studies which demonstrated decreased clearance of warfarin, diclofenac, flurbiprofen, naproxen, and piroxicam compared to wildtype (11455026, 11901091). A separate in vitro study found CYP2C9*5 has decreased enzyme activity compared to wildtype with warfarin and tolbutamide substrates that (23752738). Therefore, consensus among experts was decreased function with an activity value of 0.5 based on strong evidence.