CYP2D6*33 is assigned normal function based on limited evidence. CYP2D6*33 was first described in a subject with CYP2D6 *5/*33 genotype demonstrating similar sparteine metabolism compared to CYP2D6 *1/*5 and CYP2D6 *2/*5 subjects, indicating normal enzyme activity (9241659). In vitro studies similarly found CYP2D6*33 had normal enzyme activity and similar intrinsic clearance compared to wildtype with various substrates (24647041, 30366777). Therefore, consensus among experts was normal function with an activity value of 1 based on limited evidence as it was determined the phenotypes containing this allele would be clinically similar to phenotypes comprising normal function alleles.