Study Finds Long-Term Blood Thinner Use Reduces Clot Recurrence and Mortality

Adults who continue taking prescribed blood thinners known as oral anticoagulants after an initial three months of treatment for an unprovoked venous thromboembolism — a blood clot in the legs or lungs not triggered by surgery or injury — have substantially lower chances of experiencing another clot and of dying, according to a new study. VTE, including deep vein thrombosis and pulmonary embolism, represents a significant disease burden, with about 1.2 million cases diagnosed annually.

Published in The BMJ (formerly the British Medical Journal), the study, “Continued versus discontinued oral anticoagulant treatment for unprovoked venous thromboembolism: target trial emulation,” is a large observational study that used two U.S. health databases to compare outcomes after extended therapy versus stopping anticoagulants after at least 90 days of initial treatment. Researchers identified 70,755 individuals. Of those, 30,554 patients had completed at least 90 days of oral anticoagulants such as warfarin or direct oral anticoagulants after a first unprovoked VTE event, compared with 30,554 patients who discontinued OACs.

Researchers found that compared with people who discontinued therapy:

• Those who continued anticoagulants had an 81% lower risk of a new VTE, equivalent to about 26 fewer clot events per 1,000 person-years.
• Overall mortality was reduced by 26% for patients who maintained therapy.
• The risk of major bleeding was higher, about 75% greater in the continued group — a well-recognized side effect of long-term anticoagulant use.

When researchers combined these outcomes into a net clinical benefit measure (balancing clot recurrence and serious bleeding), extended anticoagulant use was associated with a clear overall benefit for patients. These patterns held regardless of how long anticoagulants had already been taken, including among those on therapy for nearly three years or more.

“Our findings suggest that for many patients with unprovoked blood clots, staying on anticoagulant therapy beyond three months may lower the likelihood of another potentially life-threatening clot and reduce the risk of death, even though it increases bleeding risk,” said Dae Hyun Kim, MD, MPH, ScD, associate director and senior scientist at the Hinda and Arthur Marcus Institute for Aging Research. “These real-world data provide important insight to support shared decision-making between patients and clinicians about the optimal duration of long-term anticoagulation.”

The study found that extended OAC use was also “associated with higher rates of bleeding.” But, the researchers noted, the “composite outcome of recurrent VTE and major bleeding (i.e., net clinical benefit) still favored continuation over discontinuation of OACs even after initial OAC use as long as 1080 days,” across specific OAC types.

The study was conducted by a multidisciplinary team of researchers from leading U.S. medical institutions. In addition to Dr. Kim, researchers were Kueiyu Joshua Lin, MD, ScD, associate professor of medicine, Division of Pharmacoepidemiology and Pharmacoeconomics, Department of Medicine, Brigham and Women’s Hospital and Harvard Medical School; Daniel E. Singer, MD, MPH, professor of medicine, Division of General Internal Medicine, Department of Medicine, Massachusetts General Hospital and Harvard Medical School; Yichi Zhang, PhD, research scientist, Division of Pharmacoepidemiology and Pharmacoeconomics, Brigham and Women’s Hospital and Harvard Medical School; Alexander Cervone, PhD, biostatistician, Division of Pharmacoepidemiology and Pharmacoeconomics, Brigham and Women’s Hospital and Harvard Medical School; Anna R. Kehoe, MS, research analyst, Division of Pharmacoepidemiology and Pharmacoeconomics, Brigham and Women’s Hospital and Harvard Medical School; and Katsiaryna Bykov, PharmD, PhD, assistant professor and epidemiologist, Division of Pharmacoepidemiology and Pharmacoeconomics, Brigham and Women’s Hospital and Harvard Medical School.

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