I have been on coumadin for five years now after almost dying from a shower of clots in my lungs. Your liver has proteins that coagulate or thin blood. My factor five protein no longer works so I have a greenwood stint Screen in my lower femoral artery that keeps clots from leaving my legs and traveling to my heart or lungs and stay on coumadin for the rest of my life. My legs cramp all the time even when my blood clotting levels are normal. No one can explain this to me.