The CYP2D6*10 allele is assigned as a decreased function allele with an activity value of 0.25 by CPIC. Patients carrying the CYP2D6*10 allele in combination with with alleles that result in intermediate or poor metabolizer phenotype who are treated with amitriptyline may have increased likelihood of side effects as compared to patients with alleles that result in a normal metabolizer phenotype. Other genetic and clinical factors may also influence response to amitriptyline.