CYP2D6*39 is assigned normal function based on limited evidence. A liver microsomes sample of a subject with CYP2D6 *10/*39 genotype demonstrated similar enzyme activity compared to wildtype with a bufuralol substrate (11266079). Similarly, in vitro studies found CYP2D6*39 demonstrated similar enzyme activity compared to wildtype with bufuralol, dextromethorphan, and tamoxifen substrates (18784265, 24647041). Although one in vitro study found CYP2D6*39 demonstrated decreased clearance compared to wildtype with a primaquine substrate (30366777) the experts did not find this result convincing as CYP2D6*39 demonstrated similar activity compared to wildtype towards a majority of substrates. Therefore, consensus among experts was normal function with an activity value of 1 based on limited evidence.