The CYP2C19*1 allele is assigned as a normal function allele by CPIC. Patients carrying the CYP2C19*1 allele in combination with a normal function allele who are treated with clopidogrel may have increased platelet inhibition and decreased residual platelet aggregation as compared to patients with a no or decreased function allele in combination with a normal or increased function allele or with two no or decreased function alleles. Patients carrying the CYP2C19*1 allele in combination with a normal function allele who are treated with clopidogrel may have decreased platelet inhibition and increased residual platelet aggregation compared to patients with two increased function alleles or a combination of a normal function allele with an increased function allele. However, conflicting evidence has been reported. Other genetic and clinical factors may also influence platelet inhibition.