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A new study from the University of Gothenburg reveals that while blood thinners prescribed after blood clots in the leg or lung initially increase the risk of bleeding—particularly in women and the elderly—this risk decreases over time, and differences based on gender and age eventually fade.
The research, published in the Journal of Internal Medicine, aimed to assess the increased risk of bleeding associated with anticoagulant treatment following a blood clot. Blood thinners are known to prevent further clot formation, but they also raise the risk of bleeding. The findings offer new insights into the extent of this risk at different treatment phases.
Initial Treatment Carries Higher Risk
Blood thinners are typically prescribed for at least three to six months, a period referred to as initial treatment. After this, physicians must decide whether to continue with extended treatment, carefully balancing the risk of new clots against the possibility of bleeding.
Common side effects of blood thinners include nosebleeds, blood in the urine, blood in the stool, and frequent or larger bruises due to reduced clotting. The study highlights that the risk of bleeding is influenced both by the treatment itself (treatment-induced risk) and by individual patient factors (baseline risk), which are not always adequately considered.
While prior research has focused on the general risk of bleeding—showing that older patients face a greater risk—less has been known about the specific treatment-induced risks across different patient demographics and treatment phases.
Study Findings: Bleeding Risk Decreases Over Time
The researchers analyzed Swedish registry data from over 36,000 patients undergoing anticoagulant treatment after a blood clot, comparing them to an equal number of age- and sex-matched controls who had not received blood thinners.
During the first six months of treatment, 1.07% (338 people) of the patient group experienced bleeding, compared to only 0.29% (103 people) in the control group. Women had a higher risk of bleeding than men, and patients aged 80 and above were the most vulnerable.
However, in cases where treatment continued beyond six months, the treatment-induced risk of major bleeds gradually declined. Over an extended period (up to five years), the risk reduced from just over 2% during initial treatment to 0.7%. Importantly, the study found that after this period, neither gender nor advanced age was associated with an increased risk of bleeding.
Implications for Patients and Physicians
One of the lead researchers, Katarina Glise Sandblad, an internal medicine specialist at Sahlgrenska University Hospital and a researcher at Sahlgrenska Academy, emphasized the significance of the findings.
“When I treat patients with blood clots, the decision to discontinue treatment after the initial phase or to continue with lifelong treatment can be challenging. This study shows that the bleeding risk due to blood thinners is relatively low during extended treatment and does not seem to increase with age. This is reassuring for both me and my patients,” she explained.
Reference
More information: Katarina Glise Sandblad et al, Excess risk of bleeding in patients with venous thromboembolism on direct oral anticoagulants during initial and extended treatment versus population controls, Journal of Internal Medicine (2025). DOI: 10.1111/joim.20067
Disclaimer
This article is for informational purposes only and does not constitute medical advice. Patients should consult their healthcare providers before making any decisions about anticoagulant treatment.
