Project Summary

*This project was terminated due to issues relating to trial enrollment.

PCORI has identified long-term use of blood thinner medicines as an important research topic. Blood thinners help prevent blood clots, but these medicines may cause other health problems if taken for a long time. Patients, clinicians, and others want to learn: How do different long-term blood thinner treatments compare for patients who have had a blood clot? To help answer this question, PCORI launched a funding initiative in 2015 on New Oral Anticoagulants (NOACs) in the Extended Treatment of Venous Thromboembolic Disease. This research project is one of the studies PCORI awarded as part of this program.

What is the research about?

Each year, more than 500,000 people in the United States are hospitalized because of blood clots that form in their veins. This condition is called venous thromboembolism. Most blood clots form in people’s legs. Sometimes, blood clots in the legs can break loose and go into the lungs, where they can cause serious problems and even death. More than 100,000 people in the United States die annually from blood clots that travel to the lungs.

People who have a blood clot can take blood-thinning medicine to treat it and to prevent future clots. Although several types of blood-thinning medicine work well to prevent blood clots, these medicines may cause complications, such as severe or uncontrolled bleeding.

Some people who are at high risk for a future blood clot need to take blood-thinning medicine for longer than the standard treatment of three to six months. Some  may need to take blood-thinning medicine for the rest of their lives. For long-term use, some blood-thinning medicines may work better than others and may cause fewer complications.

This study is comparing the benefits and risks of three blood-thinning medicines for people who take them on a long-term basis. Two medicines (rivaroxaban and apixaban) are relatively new treatments for blood clots. The third medicine (warfarin) has been available for a long time.

Who can this research help?

This study can help patients and their doctors decide which medicine will help them prevent blood clots and is safe to take for a long period.

What will the research team do?

The research team is working with about 60 medical research centers to enroll about 3,000 patients in the study. The study is focusing on patients who took blood-thinning medicine for 3 to 12 months to treat a blood clot in their legs or lungs, and whose doctors prescribed long-term treatment to prevent future blood clots. The research team is assigning people by chance to receive one of three different blood-thinning medicines for one year. The research team is tracking patients’ health during this time.

The research team is looking at whether patients taking the newer medicines (rivaroxaban or apixaban) have fewer bleeding complications than patients taking the older medicine (warfarin). The team is also studying whether the two newer blood thinners work as well as warfarin to prevent blood clots. Finally, the research team is comparing the two newer blood thinners to each other.

The research team is getting input from patients, doctors, pharmacists, and organizations that focus on the problem of blood clots while planning and conducting the study and analyzing the results.

Research methods at a glance

Design Element Description
Study Design Randomized controlled trial
Population Adults 18 years or older who took blood thinners for 3 to 12 months to treat a blood clot in their legs or lungs and whose doctors recommended long-term treatment with blood thinners
  • Rivaroxaban
  • Apixaban
  • Warfarin

Bleeding that requires medical attention or is life-threatening, future blood clots

Timeframe 12-month follow-up for study outcomes

Journal Citations

Related Journal Citations

Project Information

Thomas L. Ortel, MD, PhD
Duke University
Warfarin versus Direct Oral Anticoagulants for Secondary Prevention of Recurrent Venous Thromboembolism: A Randomized Comparative Effectiveness Trial

Key Dates

September 2016
June 2019

Study Registration Information


Project Status
Award Type
Health Conditions Health Conditions These are the broad terms we use to categorize our funded research studies; specific diseases or conditions are included within the appropriate larger category. Note: not all of our funded projects focus on a single disease or condition; some touch on multiple diseases or conditions, research methods, or broader health system interventions. Such projects won’t be listed by a primary disease/condition and so won’t appear if you use this filter tool to find them. View Glossary
Populations Populations PCORI is interested in research that seeks to better understand how different clinical and health system options work for different people. These populations are frequently studied in our portfolio or identified as being of interest by our stakeholders. View Glossary
Intervention Strategy Intervention Strategies PCORI funds comparative clinical effectiveness research (CER) studies that compare two or more options or approaches to health care, or that compare different ways of delivering or receiving care. View Glossary
State State The state where the project originates, or where the primary institution or organization is located. View Glossary
Last updated: June 23, 2023