Project Summary

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.

This research project is in progress. PCORI will post the research findings on this page within 90 days after the results are final.

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. Most blood clots form in people’s legs. But the clots can break loose and travel to the lungs, causing serious problems including death. More than 100,000 people in the United States die each year from blood clots that travel to their lungs.

For people who have had blood clots, blood thinners can prevent future blood clots. These medicines work well to prevent clots, but they may cause complications such as severe or uncontrolled bleeding.

Researchers don’t know whether some blood thinners work better than others to prevent future blood clots. They also don’t know whether some blood thinners are less likely than others to cause bleeding problems in people who take them for longer than three months. Few studies have looked at the use of blood thinners in people who are older, have kidney disease, or have had bleeding complications.

This study is looking at the benefits and risks of five blood thinners. The research team is comparing people who take these medicines for only three months with people who take these medicines for more than three months. The study is also comparing a blood thinner that has been available for a long time (warfarin) with four newer medicines: dabigatran, rivaroxaban, apixaban, and edoxaban. The research team is comparing the benefits and risks of the medicines for people with different characteristics.

Who can this research help?

This research can help people who need to take a blood thinner for more than three months. They and their doctors can use information from this study to help choose a medicine.

What is the research team doing?

The research team is looking at electronic health records for adults treated for a blood clot between 2010 and 2018 at Kaiser Permanente facilities in California. The patients have already taken blood-thinning medicine for at least three months. The research team is collecting information about patients’ health backgrounds, prescribed blood thinners, and changes in health. The team is asking people treated for a blood clot between 2015 and 2018 to take a survey. Questions ask about their health, well-being, and satisfaction with the treatment they received.

The researchers are looking at the number of blood clots each treatment prevented. They also are looking at the number of bleeding complications each treatment caused. The team is examining whether the risks and benefits differ for people with different characteristics, such as being older, having kidney disease, or having a high risk of bleeding. Patients who have had blood clots helped design the study and the survey.

Research methods at a glance

Design Element Description
Design Observational: cohort study
Population Adults who have had a blood clot and completed at least 3 months of treatment with blood thinners
  • Warfarin
  • Dabitgatran
  • Rivaroxaban
  • Apixaban
  • Edoxaban
Outcomes Number of blood clots, number of bleeding complications
Timeframe Up to 10-year follow-up for study outcomes

Project Information

Margaret Fang, MD, MPH
University of California, San Francisco
The Comparative Effectiveness of Warfarin and New Oral Anticoagulants for the Extended Treatment of Venous Thromboembolism

Key Dates

July 2016
July 2022

Study Registration Information


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: March 15, 2022