CYP2D6*53 is assigned normal function based on limited evidence. Multiple in vitro studies found CYP2D6*53 had similar enzyme activity compared to wildtype with multiple substrates (18784265, 24647041). Although one in vitro study found CYP2D6*53 demonstrated decreased clearance compared to wildtype with a primaquine substrate (30366777) the experts did not find this result convincing as CYP2D6*53 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.