CYP2D6*3 is assigned no function based on limited evidence. CYP2D6*3 was first described in a heterozygous subject demonstrating decreased sparteine metabolism based on an elevated urinary metabolite ratio. CYP2D6*3 is defined by a single nucleotide deletion causing a frameshift and resulting in a nonfunctional protein (2211621). 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.