The CYP2D6*41 allele is assigned as a decreased function allele by CPIC. Patients carrying the *41 allele in combination with an increased, normal, decreased or no function allele may have similar metabolism of hydrocodone as compared to patients with alleles that result in a normal metabolizer phenotype. 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 affect hydrocodone metabolism.