The CYP2D6*29 allele has been assigned as a decreased function allele with an activity score of 0.5 by CPIC. Patients carrying the *29 allele in combination with another decreased function allele or a no function allele may have decreased metabolism of codeine as compared to patients with alleles that result in a normal metabolizer phenotype, while patients carrying the *29 allele in combination with an increased function allele may have increased metabolism of codeine as compared to patients with alleles that result in a normal metabolizer phenotype. This annotation only covers the pharmacokinetic relationship between CYP2D6 and codeine and does not include evidence about clinical outcomes. Other genetic and clinical factors may also influence codeine metabolism.