Clopidogrel is a thienopyridine that is 4,5,6,7-tetrahydrothieno[3,2-c]pyridine in which the hydrogen attached to the nitrogen is replaced by an o-chlorobenzyl group, the methylene hydrogen of which is replaced by a methoxycarbonyl group (the S enantiomer). A P2Y12 receptor antagonist, it is used to inhibit blood clots and prevent heart attacks. It has a role as an anticoagulant, a platelet aggregation inhibitor and a P2Y12 receptor antagonist. It is a methyl ester, a thienopyridine and a member of monochlorobenzenes. It is functionally related to a ticlopidine.