Which of the following medications is commonly used to prevent clot formation?

Warfarin is an anticoagulant medication that is primarily used to prevent clot formation in patients who are at risk for thromboembolic events. It works by inhibiting the synthesis of vitamin K-dependent clotting factors in the liver, which are essential for blood coagulation. By doing this, Warfarin effectively reduces the ability of the blood to clot, thereby preventing the formation of new clots and allowing existing clots to dissolve more easily.

In contrast, the other medications listed serve different purposes. Ibuprofen is a nonsteroidal anti-inflammatory drug (NSAID) that is primarily used to relieve pain and reduce inflammation, but it does not specifically prevent clot formation. Hydrochlorothiazide is a diuretic that helps to lower blood pressure and manage fluid retention, and it does not have a role in anticoagulation. Amlodipine is a calcium channel blocker that is used to treat high blood pressure and angina, focusing on vascular smooth muscle relaxation rather than blood coagulation prevention. Therefore, Warfarin is the correct choice for its specific action in preventing clot formation.