CYP2D6*42 is assigned no function based on limited evidence in a heterozygous subject. CYP2D6*42 has been described in subjects with CYP2D6 *17/*42 genotype demonstrating decreased metabolism and a subject with CYP2D6 *40/*42 genotype demonstrating poor metabolism with a dextromethorphan substrate (12811367). CYP2D6*42 is defined by a base pair insertion resulting in a frameshift yielding a truncated and nonfunctional protein. Therefore, consensus among experts was no function with an activity value of 0 based on limited evidence.