Blood clots can be dangerous and even life-threatening.
When a clot forms in a deep vein or travels to the lungs, doctors usually prescribe anti-clotting drugs, also known as anticoagulants, to prevent the clot from growing or new ones from forming.
Most treatment guidelines recommend using these drugs for at least three to six months after a first blood clot. But many people and doctors wonder what happens after that period. Should treatment stop, or is it safer to continue?
A new study from the United States, published in The BMJ, provides one of the clearest answers yet. The research shows that continuing anti-clotting drugs beyond the first 90 days can greatly lower the chance of developing new blood clots.
This is especially important for people whose first clot had no clear cause, a condition called unprovoked venous thromboembolism. These cases are riskier because the clot may return without warning.
To understand the long-term effects of treatment, researchers looked at medical information from two large U.S. health insurance databases.
They studied 30,554 adults with an average age of 74. All of them had taken blood thinners for at least three months after their first unprovoked clot. The researchers then compared people who continued their treatment with those who stopped.
Because this was not a traditional randomized clinical trial, the researchers used a method called target trial emulation.
This technique helps make real-world data more similar to clinical trial data by carefully matching groups and adjusting for important factors like age, health conditions, and other medications. This allowed the team to estimate the effects of continuing treatment as accurately as possible.
The results were striking. People who kept taking their blood thinners had much lower rates of new clots—81% lower—than those who stopped. This is equal to preventing 26 clot-related events for every 1,000 people treated for one year.
They also had a 26% reduction in the overall death rate compared with those who discontinued treatment. These benefits remained even among people who continued treatment for at least three years.
However, there was a trade-off. Continuing anti-clotting drugs came with a 75% higher risk of major bleeding. Bleeding is a well-known side effect of these medications, and in some cases, it can be serious.
Still, when the researchers combined both the benefits and risks into a measure called “net clinical benefit,” they found that the advantages of long-term treatment outweighed the harms overall.
The researchers noted some limitations. The databases did not contain information about people’s income, over-the-counter medications, lab test results, or reasons for stopping treatment.
These missing pieces could affect the accuracy of the results. But the study was large, carefully analysed, and consistent with earlier research, making the findings strong and meaningful.
A group of Canadian researchers wrote an editorial to accompany the study. They agreed that the findings offer valuable guidance for doctors and patients. But they also stressed that decisions about long-term treatment must be personalized.
Not everyone faces the same risks. Some people may fear bleeding more than they fear another clot, while others may prefer the peace of mind that comes with continued protection. More research is still needed to help identify which patients benefit the most from longer treatment and which may safely stop earlier.
When reviewing and analysing the study, the key message is clear. For many people with a first unprovoked blood clot, staying on anti-clotting drugs beyond the first three months can reduce the chance of another clot and even lower the risk of death. But it also increases the likelihood of major bleeding.
The study suggests that, on average, the benefits outweigh the risks, but personal factors should guide final decisions. This research helps move the medical community closer to understanding how long blood thinners should be used and offers important information for people facing the difficult choice of whether to continue treatment indefinitely.
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