A new study from the University of Gothenburg reveals that blood thinners, commonly prescribed after blood clots in the leg or lung, increase the risk of bleeding in the early months of treatment.
However, this risk gradually decreases over time, and differences in bleeding risk between men and women, as well as between younger and older patients, disappear with long-term use. The study was published in the Journal of Internal Medicine.
Balancing the Risks of Blood Thinner Treatment
Blood thinners, or anticoagulants, are used to prevent further blood clots from forming after a patient has experienced deep vein thrombosis (DVT) in the leg or a pulmonary embolism (PE) in the lung. However, while they reduce the risk of future clots, they also make bleeding more likely.
Doctors typically prescribe blood thinners for at least three to six months—this is known as the initial treatment phase. After this period, they must decide whether to stop treatment or extend it for a longer time. The decision involves balancing two risks: stopping the medication may increase the chance of another clot, while continuing it raises the risk of excessive bleeding.
Short-Term vs. Long-Term Bleeding Risk
The study analyzed Swedish health records of over 36,000 patients who were taking blood thinners after a blood clot, comparing them with an equal number of people who had not taken blood thinners. The researchers focused on how the risk of bleeding changed over time.
During the first six months of treatment, 1.07% of the patients (338 people) experienced serious bleeding, compared to just 0.29% (103 people) in the control group.
Women were more likely to experience bleeding than men, and patients aged 80 and above were at the highest risk. The most common side effects included nosebleeds, blood in the urine or stool, and increased bruising.
However, during extended treatment (from six months up to five years), the overall risk of serious bleeding dropped significantly. The treatment-induced bleeding risk decreased from about 2% in the initial phase to just 0.7% in the extended phase.
Importantly, after six months, the differences in bleeding risk between men and women and between younger and older patients disappeared.
What This Means for Patients and Doctors
Dr. Katarina Glise Sandblad, the lead researcher and an internal medicine specialist at Sahlgrenska University Hospital, says the findings offer valuable guidance for doctors and reassurance for patients.
“When I treat patients with blood clots, deciding whether to stop or continue blood thinner treatment can be difficult,” she explains. “This study shows that after the initial months, the added bleeding risk from blood thinners is low and does not increase with age. This is reassuring for both me and my patients.”
The results suggest that, while caution is needed in the early months of treatment—especially for women and older patients—long-term use of blood thinners may not pose as great a risk as previously thought. This could help doctors make more confident decisions about whether extended treatment is necessary for their patients.
By understanding the changing risks over time, doctors can better tailor treatments to individual patients, ensuring they get the protection they need from blood clots without unnecessary fear of bleeding complications.
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The research findings can be found in Journal of Internal Medicine.
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