Like heparin, warfarin has a serious side effect of increasing the chance of uncontrolled bleeding. As a consequence, James' blood clotting time is measured frequently during the course of his treatment.
After three months, warfarin treatment was discontinued. It was felt that the increased risk of bleeding outweighed the decreased risk of another thrombotic event.
James can substantially reduce the risk of having another event by modifying his life style so as to reduce known risk factors. These risk factors include inactivity (such as long plane rides), dehydration, smoking, and some medications such as birth control pills (although James probably does not take birth control pills).