The CYP2D6*2 allele is typically characterized by two amino acid changes; both, however also occur in many other CYP2D6 alleles. Therefore, if an allele carries these two SNPs exclusively, it is designated CYP2D6*2. Interrogating for additional SNPs is the only way to distinguish CYP2D6*2 from other alleles (e.g., CYP2D6*17 and *41).