The CYP2D6*5 allele is assigned as a no function allele by CPIC. Patients carrying the CYP2D6*5 allele in combination with a no, decreased or normal function allele may have decreased metabolism of doxepin as compared to patients with alleles that result in a normal metabolizer phenotype. Patients carrying the CYP2D6*5 allele in combination with an increased function allele with an activity value of 3 or greater may have increased metabolism of doxepin as compared to patients with alleles that result in a normal metabolizer phenotype, while patients carrying the CYP2D6*5 allele in combination with an increased function allele with an activity value of 2 may have similar metabolism of doxepin as compared to patients with other alleles that result in a normal metabolizer phenotype. However, conflicting evidence has been reported. This annotation only covers the pharmacokinetic relationship between CYP2D6 and doxepin and does not include evidence about clinical outcomes. Other genetic and clinical factors may also influence metabolism of doxepin.