The CYP2D6*2 allele is assigned as a normal function allele by CPIC. Patients carrying the *2 allele in combination with alleles that result in a normal metabolizer phenotype may have similar metabolism of hydrocodone as compared to patients carrying two increased function alleles or two decreased function alleles or a normal function allele in combination with a increased or no function allele or a decreased function allele in combination with an increased or no function allele. Patients carrying the *2 allele in combination with alleles that result in a normal metabolizer phenotype may have increased metabolism of hydrocodone as compared to patients carrying two no function alleles. This annotation only covers the pharmacokinetic relationship between CYP2D6 and hydrocodone and does not include evidence about clinical outcomes. Be aware that the CPIC guideline for hydrocodone and CYP2D6 has a 'no recommendation' for CYP2D6 ultrarapid metabolizers. Other genetic and clinical factors may also influence hydrocodone metabolism.