Understanding the problem

Anticoagulants protect people who have deep vein thrombosis or pulmonary embolism from forming new blood clots while their body works on breaking down the old blood clots. How long people with DVT or PE should take an anticoagulant is not based on when the clot is gone. Instead, it is based on when the risk factor that caused the blood clot is gone.

For example, Alice develops a DVT one week after hip replacement surgery. She is treated with anticoagulants for 3 months, and then her doctor tells her she can stop taking them. Alice's risk factor for DVT was surgery. Her DVT is called "provoked". 

For many people, the risk factor that caused the DVT or PE is either weak (e.g. travel) or unknown. This type of DVT or PE is called "unprovoked". These people remain at risk for forming new blood clots for the rest of their lives. To protect themselves from another clot, they may decide to take anticoagulants indefinitely.

Anticoagulants also have safety concerns because they increase the risk of bleeding.

For example, Sam has an ulcer in his stomach that is bleeding, but so slowly, he hasn't noticed it. But when Sam is diagnosed with a PE and starts taking anticoagulants, the bleeding from his ulcer increases and he vomits up blood.

Researchers are always looking for ways to protect people from blood clots while lowering the risk of bleeding. For this reason, the study described below was designed to find out if aspirin was just as good at preventing new blood clots as Xarelto®, but with a lower risk of bleeding.