The CYP2C19*17 allele is assigned as an increased function allele by CPIC. Patients carrying the CYP2C19*17 allele in combination with a no or decreased function allele who are treated with clopidogrel may have decreased platelet inhibition and increased residual platelet aggregation as compared to patients with two normal function alleles. Patients carrying the CYP2C19*17 allele in combination with a normal or increased function allele who are treated with clopidogrel may have increased platelet inhibition and decreased residual platelet aggregation as compared to patients with two normal function alleles. However, conflicting evidence has been reported. Other genetic and clinical factors may also influence platelet inhibition.