This article does not have any sources. (February 2019)
Warfarin (or brand name Coumadin) is a powerful water-soluble compound. It prevents blood from clotting. It does that by reducing the production of factors by the liver that promote clotting. It is called an "anticoagulant agent". It is a powerful rat poison. In concentrated form, it causes bleeding of internal organs which leads to death.
It is also used, in very low doses, to prevent thrombosis, the local coagulation or clotting of the blood in the circulatory system. This is to make heart attacks, strokes, and pulmonary embolism less likely. The degree of anticoagulation is monitored by blood tests.