1. Warfarin oral tablet is available as both a generic and brand-name drug. Brand name: Coumadin, Jantoven.
  2. Warfarin comes only as a tablet you take by mouth.
  3. Warfarin is used to treat and prevent blood clots that might result in heart attack, stroke, or death. It’s also used for blood clots in atrial fibrillation, heart valve replacement, venous thrombosis, and pulmonary embolism.

FDA Warning: Bleeding risk

  • This drug has a Black Box Warning. This is the most serious warning from the Food and Drug Administration (FDA). A black box warning alerts doctors and patients to potentially dangerous effects.
  • Warfarin thins your blood and limits your blood’s ability to clot. It can cause serious bleeding, which can lead to death. You must have regular blood tests and visits with your doctor to monitor your condition. Don’t start or stop any other drug or herbal product unless your doctor tells you to. Tell your doctor if you have any signs or symptoms of bleeding.

Other warnings

Bleeding problems warning: Tell your doctor if you have an increased risk of bleeding problems, such as being at least 65 years of age, having a history of heart attack or stroke, gastrointestinal bleeding, anemia, diabetes, or kidney problems. Your doctor will decide if warfarin is right for you.

Pregnancy warning: Don’t take this medication if you’re pregnant unless you have a mechanical heart valve. Warfarin may cause birth defects, miscarriage, or death of a fetus.

Calciphylaxis warning: This medication can cause calciphylaxis. This rare but serious condition is a buildup of calcium in small blood vessels. People with kidney disease are at greater risk for this condition.

Warfarin is a prescription drug. It comes only as a tablet you take by mouth.

Warfarin oral tablet is available as the brand-name drugs Coumadin and Jantoven. It’s also available as a generic drug. Generic drugs usually cost less than the brand-name version. In some cases, they may not be available in all strengths or forms as the brand-name drug.

Why it's used

Warfarin is used to treat blood clots and to lower the chance of blood clots forming in your body. Blood clots can cause a stroke, heart attack, or other serious conditions if they form in your legs or lungs.

Warfarin is used to:

This drug may be used as part of a combination therapy. That means you may need to take it with other drugs.

How it works

Warfarin belongs to a class of drugs called anticoagulants. A class of drugs is a group of medications that work in a similar way. These drugs are often used to treat similar conditions.

Warfarin works by stopping your body from forming blood clots. It does this by blocking the formation of blood clotting factors, which are needed to make clots.

Warfarin oral tablet doesn’t cause drowsiness. However, it can cause other side effects.

More common side effects

The more common side effects that occur with warfarin are related to abnormal bleeding. Possible side effects include:

  • unusual bruising, such as:
    • unexplainable bruises
    • bruises that grow in size
  • nosebleeds
  • bleeding gums
  • bleeding from cuts that takes a long time to stop
  • heavier than normal menstrual or vaginal bleeding
  • pink or brown urine
  • red or black stools
  • coughing up blood
  • vomiting blood or materials that looks like coffee grounds

Serious side effects

If you experience any of these serious side effects, call your doctor right away. If your symptoms are potentially life threatening, or if you think you’re experiencing a medical emergency, call 911.

  • Death of skin tissue. This may happen when blood clots form and block blood flow to an area of your body. Symptoms may include:
    • pain
    • color or temperature change to any area of your body
  • Purple toes syndrome. Symptoms may include:
    • pain and purple or dark color in your toes

Disclaimer: Our goal is to provide you with the most relevant and current information. However, because drugs affect each person differently, we cannot guarantee that this information includes all possible side effects. This information is not a substitute for medical advice. Always discuss possible side effects with a healthcare provider who knows your medical history.

Warfarin oral tablet can interact with other medications, vitamins, or herbs you may be taking. An interaction is when a substance changes the way a drug works. This can be harmful or prevent the drug from working well.

To help avoid interactions, your doctor should manage all of your medications carefully. Be sure to tell your doctor about all medications, vitamins, or herbs you’re taking. To find out how this drug might interact with something else you’re taking, talk to your doctor or pharmacist.

Examples of drugs that can cause interactions with warfarin are listed below.

Anticoagulants

Your risk of bleeding is increased when you take warfarin with anticoagulants. Examples are:

  • Factor Xa inhibitors such as:
    • apixaban
    • edoxaban
    • rivaroxaban
  • Direct thrombin inhibitors such as:
    • dabigatran

Antiplatelet drugs

Your risk of bleeding is increased when you take warfarin with antiplatelet drugs. Examples are:

  • P2Y12 platelet inhibitors such as:
    • clopidogrel
    • prasugrel
    • ticagrelor

Nonsteroidal anti-inflammatory drugs (NSAIDs)

Your risk of bleeding is increased when you take warfarin with NSAIDs. Examples are:

  • diclofenac
  • ibuprofen
  • indomethacin
  • ketoprofen
  • ketorolac
  • meloxicam
  • nabumetone
  • naproxen
  • oxaprozin
  • piroxicam

Antidepressants

Your risk of bleeding is increased when you take warfarin with selective serotonin reuptake inhibitors (SSRIs) and serotonin and norepinephrine reuptake inhibitors (SNRIs). Examples are:

  • SSRIs such as:
    • citalopram
    • escitalopram
    • fluoxetine
    • fluvoxamine
    • paroxetine
    • sertraline
    • vilazodone
    • vortioxetine
  • SNRIs such as:
    • duloxetine
    • venlafaxine

Antibiotics and antifungals

Some antibiotics and antifungals can change how warfarin works in your body. Your doctor may monitor you more closely when you start or stop an antibiotic or antifungal medication. Examples are:

  • Antibiotics such as:
    • macrolides, including:
      • azithromycin
      • clarithromycin
      • erythromycin
    • sulfamethoxazole/trimethoprim
  • Antifungals such as azole antifungals, including:
    • fluconazole
    • itraconazole
    • ketoconazole
    • posaconazole
    • voriconazole

Herbal products

Some herbal products may increase the blood-thinning effect of warfarin. Examples include:

  • garlic
  • ginkgo biloba

Some herbal products may decrease the effects of warfarin and increase your risk of blood clots. Examples include:

  • coenzyme Q10
  • St. John’s wort
  • ginseng

Drugs that affect CYP450 enzyme

CYP450 enzyme helps your body to break down and process medications. Drugs that affect this enzyme may affect how your body handles warfarin.

Certain medications can increase the amount of warfarin in your body. This can put you at a higher risk of bleeding. Examples include:

  • amiodarone
  • efavirenz
  • isoniazid
  • metronidazole
  • paroxetine
  • sulfamethoxazole
  • voriconazole

Certain medications and herbs can make CYP450 work faster. This can lower the amount of warfarin in your body and put you at a higher risk of blood clots. Examples include:

  • carbamazepine
  • nevirapine
  • phenobarbital
  • rifampin
  • St. John’s wort

Disclaimer: Our goal is to provide you with the most relevant and current information. However, because drugs interact differently in each person, we cannot guarantee that this information includes all possible interactions. This information is not a substitute for medical advice. Always speak with your healthcare provider about possible interactions with all prescription drugs, vitamins, herbs and supplements, and over-the-counter drugs that you are taking.

Warfarin oral tablet comes with several warnings.

Allergy warning

Warfarin can cause a severe allergic reaction. Symptoms may include:

  • trouble breathing
  • swelling of your throat or tongue
  • hives

Don’t take this drug again if you’ve ever had an allergic reaction to it. Taking it again could be fatal.

Warnings for people with certain health conditions

For people with high blood pressure: You may have a higher risk of bleeding if you take warfarin.

For people with history of gastrointestinal bleeding: If you have a history of stomach or intestinal bleeding, warfarin may increase your risk of bleeding.

For people with heart disease or stroke: If you have heart disease or a history of stroke, your blood vessels may already be damaged and can easily bleed. Warfarin may increase your risk of bleeding.

For people with low blood count or cancer: Some cancers can cause internal bleeding. You may have a higher risk of bleeding if you take warfarin.

For people who have had head trauma: Warfarin thins your blood. This makes it harder for your blood to clot when you’re bleeding. You may have a higher risk of bleeding if you take warfarin.

For people with kidney problems: If you have a history of kidney disease, warfarin increases your risk of serious kidney damage. In addition, you have a higher bleeding risk when taking warfarin. For both of these reasons, your doctor will likely monitor your INR (international normalized ratio) closely to check how your blood is clotting.

Warnings for other groups

For pregnant women: Warfarin should not be used during pregnancy except in women with mechanical heart valves, who are at high risk of clots. A clot can harm both the mother and the baby.

Tell your doctor if you’re pregnant or plan to become pregnant. Warfarin should be used during pregnancy only if the potential benefit justifies the potential risk.

Women who are breastfeeding: Warfarin may pass through breast milk. You and your doctor may decide if you’ll take warfarin or breastfeed.

For seniors: If you’re over 60 years of age, you may be more sensitive to warfarin. Your doctor may give you a lower warfarin dose.

For children: Warfarin hasn’t been established as safe or effective for use in children younger than 18 years.

This dosage information is for warfarin oral tablet. All possible dosages and forms may not be included here. Your dose, form, and how often you take it will depend on:

  • your age
  • the condition being treated
  • how severe your condition is
  • other medical conditions you have
  • how you react to the first dose

Forms and strengths

Generic: Warfarin

  • Form: Oral tablet
  • Strengths: 1 mg, 2 mg, 2.5 mg, 3 mg, 4 mg, 5 mg, 6 mg, 7.5 mg, and 10 mg

Brand: Coumadin

  • Form: Oral tablet
  • Strengths: 1 mg, 2 mg, 2.5 mg, 3 mg, 4 mg, 5 mg, 6 mg, 7.5 mg, and 10 mg

Brand: Jantoven

  • Form: Oral tablet
  • Strengths: 1 mg, 2 mg, 2.5 mg, 3 mg, 4 mg, 5 mg, 6 mg, 7.5 mg, and 10 mg

Dosage for reduction in the risk of death, another heart attack, or stroke

Adult dosage (ages 18 and older)

Your dose of warfarin sodium is based on your prothrombin time (PT)/international normalized ratio (INR) blood test. The typical starting dose is 5 mg to 10 mg once per day. Your dose may change over time based on your test and your condition.

Child dosage (ages 0-17 years)

A safe and effective dosage hasn’t been established for this age group.

Dosage for prevention and treatment of clots with atrial fibrillation or heart valve replacement

Adult dosage (ages 18 and older)

Your dose of warfarin sodium is based on your prothrombin time (PT)/international normalized ratio (INR) blood test. The typical starting dose is 5 mg to 10 mg once per day. Your dose may change over time based on your test and your condition.

Child dosage (ages 0-17 years)

A safe and effective dosage hasn’t been established for this age group.

Dosage for prevention and treatment of clots in the lower body and in the lungs

Adult dosage (ages 18 and older)

Your dose of warfarin sodium is based on your prothrombin time (PT)/international normalized ratio (INR) blood test. The typical starting dose is 5 mg to 10 mg once per day. Your dose may change over time based on your test and your condition.

Child dosage (ages 0-17 years)

A safe and effective dosage hasn’t been established for this age group.

Special dosage considerations

  • If you’re over 60 years of age, you may be more sensitive to warfarin. Your doctor may give you a lower warfarin dose.
  • People of Asian descent usually respond to a lower dose of warfarin. Your doctor may give you a lower dose.

Disclaimer: Our goal is to provide you with the most relevant and current information. However, because drugs affect each person differently, we cannot guarantee that this list includes all possible dosages. This information is not a substitute for medical advice. Always to speak with your doctor or pharmacist about dosages that are right for you.

Warfarin may be a short-term or long-term drug treatment. How long you take this medication depends on your condition. It comes with risks if you don’t take it as prescribed.

If you skip or miss doses: Stopping or missing doses can cause complications, such as heart attack, stroke, or blood clots in your veins or lungs. Taking your medication as directed by your doctor, even when you’re feeling well, will give you the best chance of avoiding these complications.

If you take too much: Taking too much warfarin can lead to life-threatening bleeding. If you think you’ve taken too much of this drug, act right away. Call your doctor or local poison control center or go to the nearest emergency room.

What to do if you miss a dose: If you miss a dose, take it as soon as you can. Skip the missed dose if it’s almost time for your next scheduled dose. Don’t use extra medication to make up the missed dose. This could result in dangerous side effects.

How to tell if the drug is working: You may not feel any different if warfarin is working. However, you may notice reduced bleeding. Your doctor will do blood tests to see how well the drug is working.

Keep these considerations in mind if your doctor prescribes warfarin for you.

General

Warfarin tablets may be split during therapy. Talk to your healthcare provider to find available pill cutters/splitters.

Storage

  • Store in temperatures from 68–77°F (20–25°C).
  • Don’t freeze warfarin.
  • Keep it away from light and high temperature.
  • Keep your drugs away from areas where they could get wet, such as bathrooms.

Refills

A prescription for this medication is refillable. You should not need a new prescription for this medication to be refilled. Your doctor will write the number of refills authorized on your prescription.

Travel

When traveling with your medication:

  • Always carry your medication with you. When flying, never put it into a checked bag. Keep it in your carry-on bag.
  • Don’t worry about airport X-ray machines. They won’t damage your medication.
  • You may need to show airport staff the pharmacy label for your medication. Always carry the original prescription-labeled container with you.
  • Don’t put this medication in your car’s glove compartment or leave it in the car. Be sure to avoid doing this when the weather is very hot or very cold.

Clinical monitoring

You must have regular blood tests and visits with your doctor to monitor your condition. Make sure you don’t miss your appointments because your doctor determines your warfarin dose based on your blood tests.

Your diet

Some foods and beverages can interact with warfarin and affect your treatment and dosage. While taking this drug, eat a normal, balanced diet, and talk to your healthcare provider before you make any diet changes. Don’t eat large amounts of leafy green vegetables. These vegetables contain vitamin K. Also, certain vegetable oils also contain large amounts of vitamin K. Too much vitamin K can decrease the effect of warfarin.

There are other drugs available to treat your condition. Some may be better suited for you than others. Talk to your doctor about other drug options that may work for you.

Disclaimer: Healthline has made every effort to make certain that all information is factually correct, comprehensive, and up-to-date. However, this article should not be used as a substitute for the knowledge and expertise of a licensed healthcare professional. You should always consult your doctor or other healthcare professional before taking any medication. The drug information contained herein is subject to change and is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. The absence of warnings or other information for a given drug does not indicate that the drug or drug combination is safe, effective, or appropriate for all patients or all specific uses.