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Generic name: warfarin (oral) [ WAR-far-in ]
Drug class: Coumarins and indandiones

Medically reviewed by on Aug 10, 2023. Written by Cerner Multum.

What is Jantoven?

Jantoven is an anticoagulant (blood thinner). This medicine reduces the formation of blood clots.

Jantoven is used to treat or prevent blood clots in veins or arteries, which can reduce the risk of stroke, heart attack, or other serious conditions.

Jantoven may also be used for purposes not listed in this medication guide.

Jantoven side effects

Get emergency medical help if you have signs of an allergic reaction: hives; difficult breathing; swelling of your face, lips, tongue, or throat.

Jantoven increases your risk of bleeding, which can be severe or life-threatening. Call your doctor at once if you have any signs of bleeding such as:

Clots formed by Jantoven may block normal blood flow, which could lead to tissue death or amputation of the affected body part. Get medical help at once if you have:

Bleeding is the most common side effect of warfarin.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.


You should not take Jantoven if you are prone to bleeding because of a medical condition, if you have an upcoming surgery, or if you need a spinal tap or epidural. Do not take this medicine if you cannot take it on time every day.

Jantoven increases your risk of severe or fatal bleeding, especially if you have certain medical conditions, if you are 65 or older, or if you have had a stroke, or bleeding in your stomach or intestines. Seek emergency help if you have any bleeding that will not stop.

Call your doctor at once if you have other signs of bleeding such as: swelling, pain, feeling very weak or dizzy, unusual bruising, bleeding gums, nosebleeds, heavy menstrual periods or abnormal vaginal bleeding, blood in your urine, bloody or tarry stools, coughing up blood or vomit that looks like coffee grounds.

Many other drugs can increase your risk of bleeding when used with Jantoven. Tell your doctor about all medicines you have recently used.

Avoid making any changes in your diet without first talking to your doctor. Some foods can make Jantoven less effective.

Before taking this medicine

You should not take Jantoven if you are allergic to it, or if:

You also should not take Jantoven if you are are prone to bleeding because of a medical condition, such as:

Do not take Jantoven if you are pregnant, unless your doctor tells you to. This medicine can cause birth defects, but preventing blood clots may outweigh any risks to the baby. If you are not pregnant, use effective birth control to prevent pregnancy while taking this medicine and for at least 1 month after your last dose. Tell your doctor right away if you become pregnant.

Jantoven can make you bleed more easily, especially if you have ever had:

To make sure Jantoven is safe for you, tell your doctor if you have ever had:

It is not known whether warfarin passes into breast milk. Watch for signs of bruising or bleeding in the baby if you take warfarin while you are breast-feeding a baby.

How should I take Jantoven?

Follow all directions on your prescription label. Your doctor may occasionally change your dose. Do not take Jantoven in larger or smaller amounts or for longer than your doctor tells you to.

Take Jantoven at the same time every day, with or without food. Never take a double dose.

Jantoven can make it easier for you to bleed. Seek emergency help if you have any bleeding that will not stop.

You will need frequent "INR" or prothrombin time tests (to measure your blood-clotting time and determine your Jantoven dose). You must remain under the care of a doctor while taking this medicine.

If you receive Jantoven in a hospital, call or visit your doctor 3 to 7 days after you leave the hospital. Your INR will need to be tested at that time. Do not miss any follow-up appointments.

Tell your doctor if you are sick with diarrhea, fever, chills, or flu symptoms, or if your body weight changes.

You may need to stop taking Jantoven 5 to 7 days before having any surgery, dental work, or a medical procedure. Call your doctor for instructions.

Wear a medical alert tag or carry an ID card stating that you take Jantoven. Any medical care provider who treats you should know that you are taking Jantoven.

Store at room temperature away from heat, moisture, and light.

What happens if I miss a dose?

Take the missed dose as soon as you remember. Skip the missed dose if it is almost time for your next scheduled dose. Do not take extra medicine to make up the missed dose.

What happens if I overdose?

Seek emergency medical attention or call the Poison Help line at 1-800-222-1222. An overdose can cause excessive bleeding.

What should I avoid while taking Jantoven?

Avoid activities that may increase your risk of bleeding or injury. Use extra care to prevent bleeding while shaving or brushing your teeth. You may still bleed more easily for several days after you stop taking Jantoven.

Avoid making any changes in your diet without first talking to your doctor. Foods that are high in vitamin K (liver, leafy green vegetables, or vegetable oils) can make Jantoven less effective. If these foods are part of your diet, eat a consistent amount on a weekly basis.

Grapefruit juice, cranberry juice, noni juice, and pomegranate juice may interact with Jantoven and lead to unwanted side effects. Avoid the use of these juice products while taking this medicine.

Avoid drinking alcohol.

Ask your doctor before using any medicine for pain, arthritis, fever, or swelling. This includes aspirin, ibuprofen (Advil, Motrin), naproxen (Aleve), celecoxib (Celebrex), diclofenac, indomethacin, meloxicam, and others. These medicines may affect blood clotting and may also increase your risk of stomach bleeding.

What other drugs will affect Jantoven?

Many drugs (including some over-the-counter medicines and herbal products) can affect your INR and may increase the risk of bleeding if you take them with Jantoven. Not all possible drug interactions are listed in this medication guide. It is very important to ask your doctor and pharmacist before you start or stop using any other medicine, especially:

This list is not complete and many other drugs can interact with Jantoven. This includes prescription and over-the-counter medicines, vitamins, and herbal products. Give a list of all your medicines to any healthcare provider who treats you.

Popular FAQ

Treatment for bleeding associated with warfarin depends upon the level of bleeding, the INR elevation, and risk factors for forming a blood clot. There are several methods to reverse bleeding from warfarin, including vitamin K, prothrombin complex concentrate (PCC), or fresh frozen plasma (FFP). Continue reading

Warfarin was the first anticoagulant rodenticide, but today its use is declining as many rodents have grown resistant to it. Rodenticides are pesticides, often formulated into baits, that kill rodents like rats and mice. Continue reading

Feverfew, an herbal supplement that is a member of the daisy family, may interact with over 40 medicines. This includes drugs used to help prevent blood clots like the anticoagulant warfarin. Continue reading

Purple toe syndrome is thought to be due to small emboli (blood clots) in the blood vessels which cause a bluish-purple color in the toes and feet. It is a fairly rare complication associated with early warfarin use, usually occurring within the first 3 to 8 weeks of treatment. Continue reading

Cranberry products (concentrated liquid, capsules or tablets) may help to prevent a urinary tract infection (UTI) in some people, but studies have not shown it can help treat an active UTI. Continue reading

Warfarin is color-coded for safety reasons to help prevent medication errors. For example, the 5 milligram (mg) tablet is a light orange color, no matter the manufacturer, but the pill shape and imprints may vary. Continue reading

When you cut yourself, there is a series of clotting factors found in your blood that help to form a blood clot to stop the bleeding. Warfarin actually blocks (inhibits) these vitamin K-dependent clotting factors and other proteins to keep the blood anti-coagulated, but it does not actually "thin" your blood. Continue reading

Further information

Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use this medication only for the indication prescribed.

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.