Asprin

Aspirin prevents blood from clotting by blocking the production of thromboxan A-2, a chemical that platelets produce that causes them to clump. Aspirin accomplishes this by inhibiting the enzym cyclo-oxygenase-1 that produces thromboxane A-2. While other NSAIDs also inhibit the COX-1 enzyme, aspirin is the preferred NSAID for use as an antiplatelet agent because its inhibition of the COX-1 enzyme lasts much longer than the other NSAIDs. Thus, aspirin's antiplatelet effect lasts for days while the other NSAIDs' antiplatelet effects last for only hours.