Blood Thinners After Surgery: Can They Help Prevent Blood Clots?

If you’ve had major surgery, you likely took a blood thinner afterward. That seems strange to some people who wonder if that increases the risk of bleeding. After all, why take a medication that thins the blood after surgery? 

The reason people need blood thinners after surgery is to prevent blood clots. Major surgery — especially the kind of surgery after which you need to stay in bed for a few days — can significantly increase the risk of blood clots. It’s important to prevent blood clots because if a blood clot forms in your veins, it can travel to other parts of the body.  When a blood clot travels to the lung, it can be deadly. 

To be sure, blood thinners aren’t the only way to prevent blood clots. Your healthcare team will likely recommend that you use compression stockings and walk around as soon and as much as possible after surgery. 

Why do people need blood thinners after surgery?

Blood clots can happen after any kind of surgery, but some kinds of surgeries are higher risk than others. Up to 25% of people hospitalized after general surgery may develop a blood clot.  Orthopedic surgeries, like hip or knee replacements, and surgeries for cancer are higher risk than other types of surgeries. 

Blood thinners, or anticoagulants, are medications that make it harder for your blood to clot. By interrupting the blood’s clotting process, they help to lower the risk of developing a blood clot after surgery.

Who is at risk for a blood clot after surgery?

Anyone who has major surgery is at risk for a blood clot. But some people have a higher risk than others. 

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Risk factors for venous thromboembolism include:

• Older age

• Long periods of immobility (not moving), such as from travel, surgery, or hospitalization  

• Chronic venous insufficiency

• Cancer

• Heart or lung disease

• Liver disease

• Lymphedema

• Family history of blood clots (specifically the genetic condition factor V Leiden)

• Certain autoimmune conditions, like lupus and antiphospholipid syndrome

• Increased body fat

• Pregnancy

• Hormone-containing medications, like oral contraceptive medications or hormone replacement therapy 

• Use of tobacco

Are all blood thinners the same?

No. There are several different types of blood thinners that work in several different ways. They also come in different forms, so you can take them in different ways. For example, some blood thinners come as an injection, and others are in the form of a pill that you swallow. 

You need to get regular blood work with some blood thinners, but that’s not the case with all of them. And some are better for people with certain medical conditions. That’s why it’s important to work closely with your healthcare team — they’ll help make sure you get the medication that best suits your needs.

Here are some common blood thinners that are in pill form:

• Aspirin

• Coumadin (Warfarin)

• Direct oral anticoagulants — Eliquis (apixaban) and Xarelto (rivaroxaban)

Here are common blood thinners that come as injections:

• Heparin

• Low molecular weight heparin (LMWH) — enoxaparin (Lovenox)

Some of these, like aspirin and coumadin, are commonly used to prevent blood clots in people with a history of heart disease, atrial fibrillation, or history of a blood clot. But sometimes healthcare teams also use them to prevent blood clots after surgery. 

In the hospital, injectable blood thinners are common — like heparin or LMWH. But sometimes people can use them at home.

Which blood thinner is best?

There’s no one “best” blood thinner. Different blood thinners work in different ways. And some may be better for some people or in certain situations. 

So the ideal blood thinner for you really depends on your personal situation, including your age, medical history, and type of surgical procedure. Your risk of bleeding is another important consideration. Only some types of blood thinners can be reversed with medication (when needed). These types of blood thinners may not be the best choice for people with a higher risk of bleeding. 

The American Society of Hematology has guidelines that recommend which blood thinner may be best in different situations. These guidelines give suggestions for which blood thinner to use and when. They also emphasize that people who have surgery are not all the same, and some of these recommendations may not be the best choice for some people. 

Here’s some general guidance from the American Society of Hematology for different situations:

• Hip or knee replacement surgery: Aspirin, direct oral anticoagulants, or low-molecular-weight heparin (LMWH) are all good choices. 

• Hip fracture repair: The best blood thinner is LMWH or heparin. 

• Major general or gynecologic surgery: The best blood thinner is LMWH or heparin. 

• Prostate surgery: Most people should avoid blood thinners. For people at high risk of blood clots, LMWH is best. 

• Cardiovascular surgery: LMWH is best when there’s a need for a blood thinner.

• Neurosurgery (brain or spinal cord): It’s best to avoid blood thinners and opt for mechanical compression instead.  

Be sure to ask your surgeon any questions you have when planning your procedure. They’ll let you know if you need a blood thinner after surgery and, if you do, which one is best for your situation.

How long do you need to take blood thinners after surgery?

The length of time you need to take blood thinners also depends on your history and type of surgery. The American Society of Hematology recommends longer use after major surgery. 

For example, after orthopedic surgery, people may need blood thinners for at least 10 to 14 days — and even up to 35 days. For other, more minor types of surgical procedures, you may be able to stop taking blood thinners once you go home and can walk around normally after surgery.

Are there side effects?

The biggest side effect of blood thinning medication is — you guessed it — an increased risk for bleeding. Because these medications disrupt your blood’s ability to clot normally, you may bleed more after an injury. 

People at risk of a fall need to be especially careful because falling while taking blood thinners can lead to serious bleeding. Some people who have a very high risk of falling should not take blood thinners at all. 

Like most things in medicine, you and your healthcare team need to weigh the benefits of taking the medication against the risks. If you’re concerned about bleeding, talk to your surgeon before making any medication changes.

Top tips for preventing blood clots after surgery

In addition to taking blood thinners after surgery as your surgeon recommends, there are several other things you can do:

• Keep your blood flowing well in your legs by moving around as early and as much as possible after surgery.

• If you can’t walk, use massage-like devices, known as “intermittent compression devices,” to squeeze your calf muscles every few minutes to help keep blood moving.

After surgery, many people return home from the hospital with intermittent compression devices. Some studies have shown that using these devices for several days after surgery may be as effective in preventing blood clots as blood thinners — but without the added risk of bleeding. 

The American Society of Hematology recommends blood clot prevention with either blood thinners or mechanical compression devices — or both together.

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Written by:

Kelly Elterman, MD

Kelly Elterman, MD, is a board-certified anesthesiologist by the American Board of Anesthesiologyand has been practicing clinically since she finished her residency training in 2013. Along with her training, she has over 10 years experience in anesthesiology.

Edited by:

Sophie Vergnaud, MD

Sophie Vergnaud, MD, is the Senior Medical Director for GoodRx Health. A pulmonologist and hospitalist, she practiced and taught clinical medicine at hospitals in London for a decade before entering a career in health education and technology.

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