CYP2D6*17 is assigned decreased function based on moderate evidence. CYP2D6*17 has consistently been described in heterozygous and homozygous subjects demonstrating decreased metabolism of various CYP2D6 substrates compared to wildtype subjects based on urine metabolites (8764380, 8971426, 11823760). Multiple in vitro studies found CYP2D6*17 had at least modestly decreased enzyme activity compared to wildtype with various substrates (9415713, 24647041, 30366777). Therefore, consensus among experts was decreased function with an activity value of 0.5 based on moderate evidence.