The CYP2D6*17 allele is assigned as a decreased function allele with an activity score of 0.5 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 codeine as compared to patients with alleles that result in a normal metabolizer phenotype, while patients carrying the *17 allele in combination with an increased function allele may have a similar analgesic response when treated with codeine as compared to patients with alleles that result in a normal metabolizer phenotype. Other genetic and clinical factors may also influence analgesic response when treated with codeine.