CYP2D6*5 is assigned no function based on definitive evidence. CYP2D6*5 has been studied for more than 20 years and its association with impaired function is well-established (1673290, 31544239). CYP2D6*5 is defined by a deletion of the CYP2D6 gene. CYP2D6*5 was first identified in a homozygous subject demonstrating decreased sparteine metabolism (1673290). An additional study found liver samples of seven subjects heterozygous for CYP2D6*5 demonstrated decreased intrinsic clearance compared to wildtype with a bufuralol substrate (11266079). Therefore, consensus among experts was no function with an activity value of 0 based on definitive evidence.