CYP2D6*4x≥3 is assigned no function based on moderate evidence. CYP2D6*4x3 was detected in two samples (266029920). CYP2D6*4 duplication has been described in subjects demonstrating decreased metabolism of dextromethorphan or debrisoquine (10022755, 12152006). CYP2D6*4 is defined by a splicing defect resulting in a nonfunctional protein and gene duplication or multiplications would therefore not impact enzyme activity. Therefore, consensus among experts was no function with an activity value of 0 based on moderate evidence.