omeprazole decreases effects of clopidogrel by affecting hepatic enzyme CYP2C19 metabolism. High likelihood serious or life-threatening interaction. Contraindicated unless benefits outweigh risks and no alternatives available. Clopidogrel efficacy may be reduced by drugs that inhibit CYP2C19. Inhibition of platelet aggregation by clopidogrel is entirely due to an active metabolite. Clopidogrel is metabolized to this active metabolite in part by CYP2C19. .