The CYP2D6*1 allele is assigned as a normal function allele by CPIC. Patients carrying the *1 allele in combination with alleles that result in a normal metabolizer phenotype may be less likely to develop side effects when treated with venlafaxine as compared to patients with a no function allele in combination with a decreased or normal function allele or two decreased or no function alleles. However, conflicting evidence has been reported. Other genetic and clinical factors may also influence likelihood of experiencing side effects when treated with venlafaxine.