Project Summary

PCORI has identified long-term use of blood-thinning 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-thinning 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. In the meantime, results have been published in peer-reviewed journals, as listed below.

What is the research about?

More than 500,000 people in the United States are hospitalized each year because of blood clots that form in their blood vessels. Most blood clots form in people’s legs, but the clots can break loose and go into the lungs, causing serious problems, including death. On average, one in five people dies within one month of being diagnosed with a blood clot in the legs or lungs.

Some people who have had a blood clot in their legs or lungs need to take medicines called blood thinners for a long time to prevent additional clots. These medicines work well to treat blood clots and prevent new ones. But the medicines may have side effects, such as severe or uncontrolled bleeding. Treatment guidelines do not specify which blood thinners to use for long-term treatment of blood clots. Some blood thinners may work better than others to prevent additional clots or may be less likely to cause bleeding problems. In addition, research studies have not answered which blood thinner achieves the best balance between benefits and harms when taken for the long term.

This study compares the benefits and risks of all five available blood thinners when people take these medicines for the long term.

Who can this research help?

Information from this study can help people who have had a blood clot—and their doctors—choose a treatment.

What is the research team doing?

The research team is comparing the benefits and harms of five different blood thinners that people use for extended periods to prevent blood clots. The team is

  • Comparing the benefits and harms of each medicine
  • Looking at how the treatments work in different groups of people
  • Comparing their study results with findings from similar research

Patients who use these blood thinners, and also doctors, are working with the research team to design, conduct, and interpret the study.

The research team is using information from electronic healthcare databases that contain information about diagnoses, procedures, and prescribed drugs for more than 215 million people in the United States. The team is including people who used blood thinners for at least three months after having a blood clot, and continue to use them for longer. The study does not include people who used blood thinners before having a blood clot. The study is paying particular attention to how the blood thinners work for older adults, people with kidney impairment, and people who are at high risk of bleeding.

The study is comparing the benefits and harms of different blood thinners by examining how many people taking each medicine have blood clots or bleeding complications at any time for up to 10 years after being diagnosed with a blood clot. The team is also looking at how many people die from any cause after long-term treatment with the five medicines being studied.

Research methods at a glance

Design Elements Description
Study Design Observational cohort study
Population Adults who had a blood clot, completed at least three months of treatment with blood thinners, and continued to take blood thinners afterward. Participants must not have taken blood thinners before getting a blood clot.
  • Dabigatran
  • Rivaroxaban
  • Apixaban
  • Edoxaban
  • Warfarin, no extended treatment

Bleeding complications (primary), number of new blood clots, death from all causes

Timeframe Timeframe Length of follow-up for collecting data on primary outcomes. View Glossary Up to 10 years

Project Information

Katsiaryna Bykov, PharmD, ScD
Brigham and Women's Hospital
The Dabigatran, Apixaban, Rivaroxaban, Edoxaban, Warfarin Comparative Effectiveness Research Study (The DARE warfarin CER study)

Key Dates

July 2016
November 2023

Study Registration Information


Has Results
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: April 21, 2022