Education Blog for Healthcare Professionals

Aspirin – Does it Prevent DVT and PE?

To some degree it does, but it is by far not as effective as warfarin or other anticoagulants. However, a very noteworthy study was presented today (Dec 12, 2012) at the annual American Society of Hematology meeting [ref 1]. It showed that aspirin was much more effective than placebo in preventing venous thromboembolism (VTE) in patients with a history of unprovoked VTE. This is thrilling news. However, the study needs to be replicated and results confirmed in a second study.


Aspirin and DVT and PE: Previous data

There has been some evidence over the years that aspirin protects some against VTE [ref 2,3]. However, the effect observed has been mild. Therefore, the conclusion has been for years that aspirin does not in any major way protect from VTE. This is in keeping with the concept that venous clots are made up mostly of fibrin and that platelets contribute little to venous thrombosis.


The new study

The study presented today at the annual meeting of the American Society of Hematology (WARFASA study) investigated patients with a history of unprovoked VTE. They were enrolled after they had been treated for their VTE with warfarin for 6-18 months and then randomized to aspirin or placebo.  It was a double-blind study. Patients were followed for an average of 2 years. Primary endpoints were symptomatic VTE and fatal PE. The aspirin dose used was 100 mg a day. 403 patients were enrolled, 205 of whom received aspirin, 198 placebo. The study found that aspirin was effective in preventing some clots: recurrent VTE occurred in 11.0 % of patients treated with placebo and in 5.9 % on aspirin. This was a 40 % risk reduction. Major bleeding and clinically relevant non-major bleeding occurred similarly in both treatment groups. Thus, the appropriate conclusion that aspirin was safe and effective in preventing some VTEs. A few limitations of this new study need to be mentioned: It has only been presented and published as an abstract, not yet in a peer-reviewed journal; and a follow-up study needs to be done to see whether the results can be confirmed.


Personal comment

The study findings are remarkable. Aspirin can prevent some DVTs and PEs, without an increase in bleeding risk.

  • Does this study change my clinical practice? Yes. I used to tell patients who came off warfarin after treatment for an appropriate length of time (often 3-6 months) that there was no strong reason to take aspirin. I will now tell them that, once they stop warfarin, it is worthwhile to take aspirin long-term.
  • What dose will I recommend? I will tell the patient that here in the U.S. where we do not have 100 mg tablet sizes, either a baby aspirin (81 mg) or an adult aspirin (325 mg) would be appropriate.
  • Would I recommend that patients who are on long-term warfarin now stop warfarin and switch to aspirin instead? No. Clearly not. Warfarin is much more effective than aspirin. Aspirin is not a replacement for warfarin.



  1. Becattini C et al. Aspirin for the prevention of recurrence of venous thromboembolism. The WARFASA study. Blood 2011;118:251(abstract 543).
  2. Antiplatelet Trialists’ Collaboration: Collaborative overview of randomized trials of antiplatelet therapy – III. Reduction in venous thrombosis and pulmonary embolism by antiplatelet prophylaxis among surgical and medical patients. BMJ 1994;308:235-246.
  3. Prevention of pulmonary embolism and deep vein thrombosis with low dose aspirin: Pulmonary Embolism Prevention (PEP) trial. Lancet 2000,Apr 15;355(9212):1295-302.


Disclosure:  I have no conflict of interest relevant to this post.

Last updated: Dec 12th, 2011

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8 Responses to “Aspirin – Does it Prevent DVT and PE?”

  1. Tzu-Fei Wang says:

    Hi Dr. Moll,
    Thank you for updating so fast. I think this study is very interesting too. I have a question that would like to see what you’d do in your practice. The study only includes patients with unprovoked DVT, and I know we should not extrapolate from the study, but given the low toxicity of aspirin, would you consider to recommend the same thing (aspirin after warfarin) to patients with provoked VTE?
    Thank you.
    Tzu-Fei Wang

    • Stephan Moll says:

      Patients with a VTE associated with a major transient risk factor (such major surgery, trauma, or hospitalization) are at low risk of recurrence to start off with. So, if one were to assume that aspirin works in these patients as well, you would decrease a low risk to even lower. But you would have to treat a lot of patients to get this little additional benefit. Eventually, some people on aspirin will have a bleed. So, the risk benefit ratio in patients at low risk for VTE recurrence looks differently. I will look at at Aspirin and VTE differently now, but would not use it on everybody with a VTE associated with a major transient risk factor once those patients come off warfarin.

  2. Frank Brosstad says:

    Interesting, but awaits confirmation. Did any of the participants have a known hereditary thrombophilia (Prot C+S or AT deficiency or Leiden or prothrombin mutation)?

  3. Maria Ivanova says:

    What is your opinion on the use of aspirin for prevention of VTE in asymptomatic Factor V Leiden homozygous patients?

    Thank you!

    • Stephan Moll says:

      It is not known whether aspirin is beneficial in this situation. Has not been tested. I would want to know why the patient was tested for factor V Leiden in the first palcde – did he or she have a clot? Or “just” a family history of clot or factor V Leiden? Based on the recent WARFASA study, aspirin may be benefial in preventing venous clots and, thus, one could hypothesize that it might be reasonable to take by the patient who has a stronger clotting disorder, such as homozgyous factor V Leiden. However, aspirin also has some bleeding risk, even though it is low. My advice as to whether it is reasonable for a patient with homozygous factor V leiden to take aspirin would depend on the clinical circumstances of the individual patient (personal or family history of venous thromboembolism? Obese? Smoking? Low risk for bleeding?). It would certainly NOT be an evidence-based recommendation.

      • Maria Ivanova says:

        Dear Dr Moll,
        Thank you very much for your opinion about a prevention of DVT for asymptotic patient with homozygous Factor V Leiden by aspirin. The patient is a young woman -24 years old. Both her parents are Factor V Leiden heterozygous carriers. They have no personal history of venous thrombosis or PE. Their genetic results are from a population study.

        What is your opinion regarding the prevention of deep vein thrombosis in such cases – asymptomatic homozygous Factor V Leiden (stronger clotting disorder) patient with no personal or family history of thrombosis or PE, normal weight, non-smoker.

        Thank you very much!

        • Stephan Moll says:

          The VTE risk profile of this person is pretty low – normal weight, no family history of venous thromboembolism (VTE). The absolute risk per year to develop a VTE is low in such a patient and, thus, prophylactic long-term anticoagulation (such as with warfarin) in somebody who has never had a clot is typically NOT indicated. To take an aspirin 81 or 100 mg per day may be beneficial, if this person’s risk for bleeding is low.