Warfarin is an anticoagulant medication that doctors prescribe to reduce the risk of blood clots, which may cause vein blockages, heart attack, and stroke.

Blood clotting is useful for stopping bleeding, but too much blood clotting can be dangerous. It can increase the risk of:

Warfarin can help prevent these.

Brand names for warfarin are Coumadin and Jantoven. And though people sometimes call these drugs blood thinners, they do not really thin the blood. They cause it to take longerTrusted Source to clot.

Here, find out why a doctor might prescribe warfarin and how it works. This article also discusses side effects and risks.

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Doctors prescribe warfarin to treat and prevent blood clots.

This includes people who have or are at risk of:

  • pulmonary embolism, where there is a clot in the lung
  • a heart attack
  • venous thrombosis, such as DVT, when a blood clot occurs in a vein
  • complications relating to atrial fibrillation or heart valve replacement surgery
  • blood clotting disorders, such as thrombophilia
  • clotting after surgery

If a clot forms, it can block a blood vessel, leading to swelling and other problems.

Parts of a clot can also break off and travel through the bloodstream until they block a vessel in another part of the body. In the brain, a clot can cause a stroke.

Warfarin prevents the production of certain clotting factors in the blood. These are factors that depend on vitamin K for synthesis.

The body needs vitamin K to produce prothrombin and other clotting factors. If a person has an injury, these clotting factors enable a clot to form, which stops additional bleeding.

Warfarin interferes with the ability of prothrombin and clotting factors to form a clot.

Warfarin comes in tablet form, which a person can take orally once daily. They should take it at the same time each day.

An individual also needs regular blood tests, and the doctor may increase or decrease the dose over time, depending on the results.

It is essential to follow the instructions precisely and continue taking warfarin, even if the person feels well.

Warfarin aims to reduce the risk of blood clotting, but it can also increase the risk of bleeding. For this reason, the Food and Drug Administration (FDA) requires it to carry a boxed warning.

It is essential not to take another drug or substance that increases the risk of bleeding while using warfarin.

Individuals may find they bleed more easily after an injury, while there is also a higher risk of internal bleeding.

Bleeding problems are more likely to arise in those aged 65 years and over and during the first month of treatment.

Other possible adverse effects include:

If hives, swelling, and difficulty breathing occur after taking warfarin, a person should seek emergency medical help. These may be signs of anaphylaxis, a severe allergic reaction.

Anaphylaxis: Symptoms and what to do

Anaphylaxis is a severe allergic reaction that can be life threatening. The symptoms develop suddenly and include:

  • hives
  • swelling of the face or mouth
  • wheezing
  • fast, shallow breathing
  • a fast heart rate
  • clammy skin
  • anxiety or confusion
  • dizziness
  • vomiting
  • blue or white lips
  • fainting or loss of consciousness

If someone has these symptoms:

  1. Check whether they are carrying an epinephrine pen. If they are, follow the instructions on the side of the pen to use it.
  2. Dial 911 or the number of the nearest emergency department.
  3. Assist the person in moving from a sitting position to lying down. If they have vomited, turn them onto their side.
  4. Stay with them until the emergency services arrive.

Some people may need more than one epinephrine injection. If the symptoms do not improve in 5 to 15 minutes, or they come back, use a second pen if the person has one.

There are many drugs a person should not take alongside warfarin, as unwanted and possibly hazardous interactions can occur.

For this reason, people using warfarin should do the following:

  • Take the exact dose the doctor prescribes.
  • Never take an extraTrusted Source dose after missing one.
  • Make sure the doctor knows about any other drugs the person is taking before using warfarin, and check before taking any new drugs.
  • Tell the doctor about supplements before using warfarin, and check before starting any new supplements.
  • Let any dentist, surgeon, or other doctor know about a warfarin prescription before undergoing a procedure that might involve bleeding.
  • Speak with a doctor if they become pregnant or plan to become pregnant.
  • Let the doctor know if they are breastfeeding or plan to start breastfeeding.
  • Avoid consuming large amounts of foods that contain vitamin K, such as green leafy vegetables and some cooking oils. Vitamin K increases the body’s ability to form clots.
  • Let the doctor know if they are unwell or have an injury.
  • Keep all appointments for blood tests.
  • Take care when doing activities that could result in an injury, such as using a knife, gardening, and some sports.
  • Avoid activities, such as trimming corns, and using toothpicks.
  • Use an electric razor rather than a blade.

A person using warfarin over the long term may wish to consider wearing a medical alert bracelet, necklace, or similar. If an accident occurs and they are unable to explain, the tag will show the healthcare team that they are taking warfarin.

A person should seek immediate medical help if they notice any of the following:

They should also seek emergency help if they have signs of an allergic reaction, such as hives, swelling, or difficulty breathing.

Warfarin can interact with many drugs, supplements, and even foods. People should check with a doctor before taking this medication with any supplements or other medication.

Supplements that may interact with warfarin include the following, but these are not the only ones:

Many drugs can interact with warfarin. Some common ones are:

Some lifestyle and dietary factors can also interact with warfarin:

Taking extra vitamin K increases the production of prothrombin and clotting factors in the body. As a result, it can override the effects of warfarin.

People should not use warfarin if they:

  • are pregnant, unless they have mechanical heart valves
  • have a condition that increases their tendency to bleed
  • dental work or any surgical procedures
  • have hypersensitivity to warfarin or any of its ingredients
  • have a type of high blood pressure called malignant hypertension

Warfarin, which has the brand names Coumadin and Jantoven, is an anticoagulant drug that doctors prescribe to prevent or treat blood clots.

It can increase the risk of bleeding, so it is essential to follow a doctor’s instructions when using this drug. They should also let a doctor know about any other medications or supplements they are taking or planning to take.

Anyone who has concerns about using warfarin should speak with their doctor.