CYP2D6*137 is assigned uncertain function due to inadequate literature describing function of this allele. One in vitro study demonstrated decreased intrinsic clearance CLint (Vmax/Km) of 50.1% and 78.2% compared to *1 for tamoxifen N-desmethylation and dextromethorphan O-demethylation, respectively (32759992). Therefore, consensus among experts was uncertain function due to inadequate evidence.