Most people need to take blood thinners for at least 3 months after a pulmonary embolism (PE). Many take them for 3 to 6 months, but some need longer treatment or may need to continue indefinitely. The right length depends on what caused the clot, whether risk factors remain, whether a clot has happened before, and the chance of bleeding. Do not stop the medicine without your prescriber's guidance.
Why Are Blood Thinners Usually Taken for at Least 3 Months?
Blood thinners, medically called anticoagulants, are medicines that help prevent blood clots from growing and reduce the chance of new clots forming. They give the body time to break down an existing clot while helping protect against further clotting.
The NHS guidance on pulmonary embolism recommends anticoagulant tablets for at least 3 months after a PE. This is the minimum treatment period for most people with a confirmed PE, not a guarantee that everyone can stop at that point. Some people need treatment for 6 months or longer, depending on the circumstances.
Feeling better does not necessarily mean it is safe to stop treatment. The decision should be based on the reason the clot occurred, the likelihood of another clot, the risk of bleeding, and how well the treatment is tolerated.
What Determines How Long You Need Blood Thinners?
The main question is whether the factors that contributed to the PE were temporary or whether the risk of another clot is likely to continue. Your healthcare professional will also consider your medical history, any previous blood clots, and your risk of bleeding.
PE Caused by a Temporary Risk Factor
A PE may occur after a temporary event that increases the chance of a blood clot. Examples include:
- Major surgery or a significant injury.
- A hospital stay involving prolonged bed rest or limited movement.
- A period of reduced mobility that later resolves.
When a PE is linked to a temporary risk factor that has resolved, treatment can often end after 3 months if recovery has been uncomplicated. The National Institute for Health and Care Excellence (NICE) recommends considering this option when the original trigger is no longer present and the clinical course has been uncomplicated.
For example, someone who develops a PE after major surgery may need a shorter course than someone whose clot occurred without a clear temporary cause. However, the decision still depends on the person's overall circumstances rather than the original trigger alone.
PE Without a Clear Cause
A PE is sometimes described as unprovoked when no clear temporary trigger can be identified. In this situation, the chance of another clot after stopping treatment may be higher than it is after a PE caused by a temporary factor that has resolved.
The 2026 American Heart Association and American College of Cardiology pulmonary embolism guideline recommends continuing anticoagulation beyond the initial 3-to-6-month treatment phase for people with a first PE who do not have a major reversible risk factor. This includes situations in which no clear temporary cause is identified.
Extended treatment can help reduce the risk of another clot. It is not automatically necessary for every person with an unprovoked PE, because the potential benefit must be weighed against bleeding risk and other individual factors.
PE With an Ongoing Risk Factor
Some medical conditions or circumstances can continue to increase the likelihood of blood clots. Active cancer is one example. Other persistent health conditions may also affect the decision about when to stop anticoagulation.
When a risk factor is ongoing, blood thinners may be recommended beyond the first 3 to 6 months. For people with active cancer, NICE recommends reviewing the benefits and risks of treatment after 3 to 6 months rather than assuming treatment can end at 3 months. The appropriate duration depends on the person's circumstances and whether the risk of clotting continues.
PE That Has Happened More Than Once
A history of multiple blood clots can make longer treatment more likely. In particular, people who have had recurrent unprovoked PE or deep vein thrombosis (DVT) may benefit from continued anticoagulation to help prevent another event.
The American Society of Hematology (ASH) guidelines for treating DVT and PE recommend indefinite anticoagulation for people with recurrent unprovoked venous thromboembolism. Other patterns of recurrence require a more individualized decision, especially when bleeding risk is high.
Does Taking Blood Thinners Indefinitely Mean Lifelong Treatment?
Indefinite anticoagulation means there is no planned stopping date at the time the treatment decision is made. For some people, this may mean taking blood thinners for many years or for the rest of their lives. It is more likely to be considered when the risk of another clot remains high.
However, indefinite treatment does not mean that the decision can never change. Your healthcare professional should periodically review whether continuing the medicine remains appropriate. Changes in your health, the factors that increase clot risk, or your risk of bleeding may affect the plan.
How Do Doctors Decide Whether You Can Stop After 3 Months?
A review near the 3-month mark is an important opportunity to discuss whether you need further treatment. Your healthcare professional will consider the circumstances surrounding the original PE and whether the factors that contributed to it have resolved.
The review may include discussion of:
- The cause of the PE: Whether it followed a temporary trigger or occurred without a clear cause.
- Your risk of another clot: Whether you have persistent risk factors or a history of previous clots.
- Your bleeding risk: Whether you have a history of bleeding or other factors that make anticoagulants less safe.
- Your treatment preferences: How you feel about the benefits, risks, and practical demands of continued treatment.
Blood thinners can cause bleeding, and the U.S. National Library of Medicine's MedlinePlus guidance on pulmonary embolism notes that the risk can be especially relevant when anticoagulants are taken with other medicines that also affect clotting, such as aspirin. This is one reason clinicians weigh the risk of another PE against the risk of bleeding before recommending longer treatment.
Tests or risk scores may sometimes help with specific decisions, but they do not replace a clinical assessment. The recommendation should reflect your medical history and current circumstances, not simply the number of months you have taken the medicine.
What Should You Do Before Stopping Blood Thinners?
Do not stop, reduce, or change your prescribed anticoagulant dose on your own, even if you have completed 3 months of treatment or no longer have symptoms. Stopping too early may leave you at risk of another clot, while continuing treatment unnecessarily may expose you to avoidable bleeding risk.
If you are approaching the end of your prescribed course, arrange a review with the clinician managing your PE. Ask whether the original cause has resolved, whether you have any ongoing risk factors, and whether stopping or extending treatment is the safer option. If you experience troublesome side effects or signs of bleeding, contact a healthcare professional promptly; significant or uncontrolled bleeding requires urgent medical attention.
The key point is that 3 months is a common minimum treatment period, not a universal stopping date. Some people can stop after a short, planned course, while others benefit from long-term protection. The safest duration is the one chosen after reviewing both the risk of another clot and the risk of bleeding.