The CYP2D6*17 allele is assigned as a decreased function allele by CPIC. Patients carrying the *17 allele in combination with a decreased or no function allele may have a decreased analgesic response when treated with hydrocodone as compared to patients with alleles that result in a normal metabolizer phenotype, while patients carrying the *17 allele in addition to a normal or increased function allele may have a similar analgesic response when treated with hydrocodone as compared to patients with alleles that result in a normal metabolizer phenotype. 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 response to hydrocodone.