The CYP2D6*1xN alleles (*1x2 and *1x鈮?) have been assigned as increased function alleles by CPIC. Patients carrying a CYP2D6*1xN allele in combination with a normal or increased function allele or a decreased function allele with an activity value of 0.5 may have increased metabolism of amitriptyline as compared to patients with alleles that result in a normal metabolizer phenotype. Patients carrying a CYP2D6*1xN allele with an activity value of 3 or greater in combination with a decreased function allele with an activity value of 0.25 or a no function allele may also have increased metabolism of amitriptyline as compared to patients with alleles that result in a normal metabolizer phenotype, while patients carrying a CYP2D6*1xN allele with an activity value of 2 in combination with a decreased function allele with an activity value of 0.25 or a no function allele may have similar metabolism of amitriptyline as compared to patients with alleles that result in a normal metabolizer phenotype. This annotation only covers the pharmacokinetic relationship between CYP2D6 and amitriptyline and does not include evidence about clinical outcomes. Other genetic and clinical factors may also influence metabolism of amitriptyline.