The CYP2D6*41 allele is assigned as a decreased function allele with an activity value of 0.5 by CPIC. Patients carrying the CYP2D6*41 allele in combination with a no or decreased function allele may have decreased metabolism of amitriptyline as compared to patients with alleles that result in a normal metabolizer phenotype. Patients carrying the CYP2D6*41 allele in combination with an increased function allele may have increased 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.