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The extra red blood cells make your blood thicker than normal. As a result, blood clots can form more easily. These clots can block blood flow through your arteries and veins, which can cause a heart attack or stroke. Thicker blood also doesn't flow as quickly to your body as normal blood.
Because warfarin interferes with the formation of blood clots, it is called an anticoagulant. Many people refer to anticoagulants as âblood thinnersâ; however, warfarin does not thin the blood but instead causes the blood to take longer to form a clot.