Anticoagulant drugs, or blood thinners, help prevent the blood from clotting. Blood clots can lead to potentially fatal complications, such as stroke or heart attack.

Doctors may prescribe anticoagulant drugs to those who have a high risk of blood clots.

Blood clots can block the blood vessels and stop the blood from flowing to important organs, such as the lungs, brain, and heart. This can increase a person’s risk of heart attack or stroke.

Anticoagulants are medications that help prevent blood clots. Although people call them “blood thinners,” these medications do not actually thin the blood. Instead, they prevent the blood from thickening, or clotting.

This article reviews what anticoagulant drugs are, what they do, and more.

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The primary function of anticoagulants is to prevent blood clots from forming.

According to a 2015 review, some anticoagulants interfere with proteins in the blood — called factors — that are responsible for the coagulation, or thickening, process.

There are several factors in the blood, and different forms of anticoagulants target different factors.

Some anticoagulants bind to antithrombin, a substance in the blood that restricts the blood’s ability to clot. Antithrombin also inhibits:

  • thrombin, which is required for the blood to clot
  • factor Xa and IXa, which are necessary to create thrombin

Antiplatelet drugs are another type of blood thinners.

A doctor may prescribe these medications for similar reasons to anticoagulant drugs. However, they work slightly differently.

Instead of preventing the blood from thickening, these medications help prevent platelets from binding together to form a clot. The most common antiplatelet drug is aspirin.

A doctor will prescribe anticoagulants to people who have a high risk of developing blood clots.

The United Kingdom’s National Health Service (NHS) notes that a doctor may prescribe anticoagulants if a person is at risk of the following conditions:

  • stroke, which happens when a blood clot restricts the blood flow to the brain
  • transient ischemic attacks, or mini strokes — these have similar symptoms to a stroke, but the effects typically last less than 24 hours
  • heart attacks, in which a blood clot blocks a blood vessel that supplies blood to the heart
  • deep vein thrombosis, which is when a blood clot forms in a deep vein, usually in the legs
  • pulmonary embolism, which is when a blood clot blocks a blood vessel around the lungs

A person may have a high risk of developing the above conditions if they:

  • have a history of blood clots
  • recently had surgery that prevented them from moving around during recovery
  • have undergone an aortic valve replacement
  • have atrial fibrillation, a type of irregular heartbeat
  • have a condition that increases the chance of thrombophilia, which means the blood has an increased risk of forming blood clots
  • have antiphospholipid syndrome, which is when the immune system attacks the proteins and fats in the blood vessels

There are several types of anticoagulant drugs, which vary based on their method of action and the factors they target.

Available types include:

  • Unfractioned heparin: This type is fast-acting, has a short half-life, and binds to antithrombin.
  • Low molecular heparin: These anticoagulants work longer than unfractioned heparin. Examples include:
    • enoxaparin
    • dalteparin
    • tinzaparin
    • nadroparin
  • Vitamin K-dependent antagonists (VKA): These anticoagulants block vitamin K-epoxide reductase, which is a type of enzyme. This prevents clotting factors that require vitamin K, including factors 2, 7, 9, and 10. Warfarin is a type of VKA.
  • Direct thrombin inhibitors: The kidneys break down these anticoagulants, which inhibit thrombin. Examples include:
    • bivalirudin
    • argatroban
    • dabigatran
  • Direct factor 10a inhibitors: These bind directly to factor 10a. Examples include:
    • rivaroxaban
    • apixaban
    • edoxaban
    • betrixaban

Both heparin and warfarin have been around for a while.

Newer medications, called direct oral anticoagulants (DOACs), new oral anticoagulants (NOACs), or target-specific oral anticoagulants (TSOACs), inhibit factor 2a (thrombin) or 10a.

These medications, in general, have a lower risk of side effects than warfarin.

Which do doctors most commonly prescribe?

In a 2020 study, researchers looked at the prevalence of different types of anticoagulants. They found that warfarin was, and still is, the type of blood thinner that doctors most commonly prescribe in the United States.

However, they also noted that while warfarin continues to be the most popular, the number of times that doctors prescribed it decreased from 2012 to 2018.

In the same period, doctors prescribed apixaban and rivaroxaban in increasing numbers. These two medications have fewer side effects, and people generally tolerate them well.

The NHS states that people should take anticoagulant capsules and tablets once or twice a day, depending on the medication, at the same time each day.

Anticoagulants come in different strengths. A doctor or nurse will provide information regarding the correct dose.

People should take warfarin, dabigatran, and apixaban with water. A person can take edoxaban with or without food, but they should take rivaoxaban alongside food.

Missed doses

If a person is taking warfarin and misses a dose, they should take it as soon as they remember to do so.

However, if they miss the dose and do not remember until the following day, they should skip the missed dose and take their next dose as usual.

People should avoid taking a double dose.

For newer anticoagulants, people should do the following:

  • Apixaban or dabigatran twice a day: People should take the dose as soon as they remember, as long as it is more than 6 hours before the next dose. If the next dose is less than 6 hours away, they should skip the missed dose.
  • Rivaroxaban once a day: A person can take the missed dose as soon as they remember, as long as it is more than 12 hours before the next scheduled dose. Otherwise, they should skip the missed dose and take the next dose as usual.
  • Edoxaban once a day: A person can take the missed dose as soon as they remember. However, if they do not remember until the next day, they should skip the missed dose. It is important that a person does not take more than one dose of edoxaban in a day.

Extra doses

If people take more than their prescribed dose, they should contact a medical professional for advice. This is because taking too much can increase a person’s risk of bleeding.

Monitoring doses

People taking warfarin will need regular blood tests to see how quickly the blood clots. These tests are necessary to make sure the blood does not clot too slowly or too quickly.

Initially, a person will require blood tests each day until they are taking the correct dose.

A person can undergo blood tests at the doctor’s office or use a home test. If a person wishes to use a home test, they will need training so they know how to use it.

For newer anticoagulants, such as apixaban, blood tests are not necessary. However, it is still important for a person to see a doctor every few months to ensure that they are taking the correct dose.

Anticoagulant medications can cause side effects that may lead to more serious complications.

The most common risk is excessive bleeding. A 2018 study found that in the tested population, about 75% of warfarin users experienced this effect, while 48% of those taking direct-acting oral anticoagulants experienced the effect.

Other side effects include:

Anticoagulant drugs can interact with other medications a person may be taking. Interactions can have one of two effects: They make the medication more effective, which increases bleeding risk, or they make the medication less effective, which increases the risk of clotting.

A person should speak with a doctor about the medications they are taking, including over-the-counter medications. Common medications, such as aspirin, can interact with anticoagulant medications.

Supplements and dietary changes can also affect warfarin. A person who is taking warfarin should consult a doctor before making changes to their diet or taking a new supplement.

People may wish to avoid eating foods that are high in vitamin K. Alcohol and grapefruit juice can increase the effects of warfarin, resulting in an increased chance of bleeding complications.

Learn more about foods a person should avoid when taking warfarin.

Anticoagulants are a type of blood thinning medication to prevent blood clots. If a person has certain risk factors for clotting, these medications can help prevent serious complications, such as heart attack or stroke.

Warfarin and heparin appear to be among the anticoagulants that doctors most commonly prescribe. Apixaban, dabigatran, and rivaroxaban are newer anticoagulants.

Anticoagulant medications have a risk of causing excessive bleeding. Newer forms of these medications present less of a risk, but people who are taking these medications should still speak with a doctor before making changes to their medications or major changes to their daily diet.