CYP2D6*41 is assigned decreased function based on strong evidence in heterozygous and homozygous subjects and in vitro studies. Subjects carrying CYP2D6*41 have demonstrated decreased enzyme activity compared to wildtype and CYP2D6*2 subjects with various substrates (11037799, 15289790, 17112815, 19364831). In vitro studies found CYP2D6*41 has decreased protein expression compared to wildtype (17001295, 19364831). Therefore, consensus among experts was decreased function with an activity value of 0.25 based on strong evidence.