CYP2D6*59 is assigned decreased function based on moderate evidence. CYP2D6*59 has been described in subjects demonstrating decreased sparteine and dextromethorphan metabolism (17001296, 26335396). An in vitro study found CYP2D6*59 exhibited decreased mRNA levels and enzyme activity with a propafenone substrate compared to wildtype (17001296). Therefore, consensus among experts was decreased function with an activity value of 0.5 based on moderate evidence.