The CYP2D6*1 allele is assigned as a normal function allele by CPIC. Patients carrying the CYP2D6*1 allele in combination with alleles that result in a normal metabolizer phenotype who are treated with amitriptyline may have decreased likelihood of side effects as compared to patients with a combination of alleles that result in intermediate or poor metabolizer phenotype. Other genetic and clinical factors may also influence response to amitriptyline.