The CYP2C19*2 allele is assigned as a no function allele by CPIC. Patients carrying the CYP2C19*2 allele in combination with a normal or no function allele who are treated with citalopram may have increased risk for treatment related side effects or intolerance as compared to patients with two normal function alleles. However, conflicting evidence has been reported. Other genetic and clinical factors may also influence treatment related side effects.