CYP2D6*8 is assigned no function based on limited evidence. CYP2D6*8 was first described in a subject demonstrating decreased debrisoquine and sparteine metabolism (8530011). CYP2D6*8 is defined by an amino substitution resulting in 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 as it was determined the phenotypes containing this allele would be clinically distinct from phenotypes comprising normal and decreased function alleles.