CYP2D6*56 is assigned no function based on limited evidence. A subject with CYP2D6 *4/*56 genotype demonstrated poor dextromethorphan metabolism based on urine metabolites on multiple occasions (17392730). CYP2D6*56 was identified in an hepatocyte demonstrating undetectable CYP2D6 protein expression and undetectable enzyme activity with dextromethorphan and bufuralol substrates (16679388). CYP2D6*56 is defined by a premature stop codon yielding a truncated and nonfunctional protein. Therefore, consensus among experts was no function with an activity value of 0 based on limited evidence.