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Generic Name: Warfarin (WAR far in)
Brand Name: Coumadin, Jantoven

Medically reviewed by Last updated on May 28, 2020.


  • This medicine may cause very bad and sometimes deadly bleeding. Talk with the doctor.
  • Call your doctor right away if you have any signs of bleeding problems, like bruising; black, tarry, or bloody stools; bleeding gums; blood in the urine; coughing up blood; cuts that take a long time to stop bleeding; feel dizzy; feeling very tired or weak; nosebleeds; pain or swelling; throwing up blood or throw up that looks like coffee grounds; or very bad headache.
  • Call your doctor right away if you have vaginal bleeding that is not normal or very heavy periods (menstrual bleeding).
  • You will need to have your blood work (PT/INR) checked while you take Jantoven (warfarin). This is important to make sure the drug works right and to check your risk of bleeding. Have your PT/INR checked as you have been told by your doctor or other health care provider. If you are not sure when you need to have your PT/INR checked, call your doctor or other health care provider.
  • Your diet and certain drugs may affect your PT/INR level. Talk with your doctor.
  • Avoid actions or sports that may raise the chance of injury or bleeding.

Uses of Jantoven:

  • It is used to treat blood clots.
  • It is used to thin the blood so that clots will not form.
  • It is used to lower the chance of heart attack, stroke, and death in some people.

What do I need to tell my doctor BEFORE I take Jantoven?

  • If you are allergic to Jantoven (warfarin); any part of Jantoven (warfarin); or any other drugs, foods, or substances. Tell your doctor about the allergy and what signs you had.
  • If you have any of these health problems: Blood vessel problems like, aneurysm or dissecting aorta; bleeding problems; bleeding in the brain; active ulcer; bleeding of the stomach, bowel, urinary tract, genitals, or respiratory tract; blood problems; heart infection; low platelet count; pericarditis, recent surgery of the eye, brain, or spine; or very high blood pressure.
  • If you have any of these health problems: A certain health problem called pre-eclampsia, seizures during pregnancy (eclampsia), induction of labor, or threatened spontaneous abortion.
  • If you are having surgery, talk with your doctor.
  • If you will be getting spinal anesthesia or a spinal treatment.
  • If you have had spinal anesthesia, surgery, or any spinal care, talk with your doctor.
  • If you know that you will not take the drug or have your blood work (PT/INR) checked as you have been told.
  • If you have a low platelet count caused by heparin.
  • If you are pregnant.

This is not a list of all drugs or health problems that interact with Jantoven (warfarin).

Tell your doctor and pharmacist about all of your drugs (prescription or OTC, natural products, vitamins) and health problems. You must check to make sure that it is safe for you to take Jantoven (warfarin) with all of your drugs and health problems. Do not start, stop, or change the dose of any drug without checking with your doctor.

What are some things I need to know or do while I take Jantoven?

  • Tell all of your health care providers that you take Jantoven (warfarin). This includes your doctors, nurses, pharmacists, and dentists. This medicine may need to be stopped before certain types of surgery as your doctor has told you. If Jantoven (warfarin) is stopped, your doctor will tell you when to start taking Jantoven (warfarin) again after your surgery or procedure.
  • Use care to prevent injury and avoid falls or crashes.
  • If you fall or hurt yourself, or if you hit your head, call your doctor right away. Talk with your doctor even if you feel fine.
  • You may bleed more easily. Be careful and avoid injury. Use a soft toothbrush and an electric razor.
  • If you drink grapefruit juice or eat grapefruit often, talk with your doctor.
  • Talk with your doctor before using products that have aspirin, blood thinners, garlic, ginseng, ginkgo, ibuprofen or like products, pain drugs, or vitamin E.
  • Certain foods can affect your PT/INR levels. Follow the diet plan that your doctor or other health care provider told you about.
  • Talk with your doctor about the amount of vitamin K in your diet. Vitamin K may change how Jantoven (warfarin) works. You do not have to avoid all foods with vitamin K. However, you will need to keep the amount of foods with vitamin K in your diet about the same from day to day. Many foods have vitamin K in them. This includes some green, leafy vegetables; broccoli; liver; and certain vegetable oils. Get a list of foods that have vitamin K in them from your doctor. Do not make big changes in your normal diet without talking with your doctor.
  • Talk with your doctor before taking multivitamins, natural products, and diet aids. These may have vitamin K in them.
  • Have patient safety card with you at all times.
  • Call your doctor right away if you have diarrhea, a fever, or an infection.
  • If you start or stop smoking, talk with your doctor. How much drug you take may need to be changed.
  • A very bad and sometimes deadly health problem involving the skin (calciphylaxis) has happened with Jantoven (warfarin). This has happened in people with and without very bad kidney problems. Talk with the doctor.
  • If you are of Asian descent, use Jantoven (warfarin) with care. You could have more side effects.
  • If you are 60 or older, use Jantoven (warfarin) with care. You could have more side effects.
  • This medicine may cause harm to an unborn baby. A pregnancy test will be done before you start Jantoven (warfarin) to show that you are NOT pregnant.
  • Women must use birth control while taking Jantoven (warfarin) and for some time after the last dose. Ask your doctor how long to use birth control. If you get pregnant, call your doctor right away.
  • Tell your doctor if you are breast-feeding. You will need to talk about any risks to your baby.

How is this medicine (Jantoven) best taken?

Use Jantoven (warfarin) as ordered by your doctor. Read all information given to you. Follow all instructions closely.

  • Use Jantoven (warfarin) exactly as you have been told, even if you feel well. This is important for the drug to work right and to lower the risk of bleeding.
  • Take Jantoven (warfarin) at the same time of day.
  • Pregnant women must not handle crushed or broken tablets. Talk with the doctor.

What do I do if I miss a dose?

  • Take a missed dose as soon as you think about it on the same day you missed the dose.
  • If you do not think about the missed dose until the next day, skip the missed dose and go back to your normal time.
  • Do not take more than 1 dose of Jantoven (warfarin) in the same day.

What are some side effects that I need to call my doctor about right away?

WARNING/CAUTION: Even though it may be rare, some people may have very bad and sometimes deadly side effects when taking a drug. Tell your doctor or get medical help right away if you have any of the following signs or symptoms that may be related to a very bad side effect:

  • Signs of an allergic reaction, like rash; hives; itching; red, swollen, blistered, or peeling skin with or without fever; wheezing; tightness in the chest or throat; trouble breathing, swallowing, or talking; unusual hoarseness; or swelling of the mouth, face, lips, tongue, or throat.
  • Weakness on 1 side of the body, trouble speaking or thinking, change in balance, drooping on one side of the face, or blurred eyesight.
  • Chest pain.
  • Very bad dizziness or passing out.
  • Swelling, warmth, numbness, change of color, or pain in a leg or arm.
  • Very bad headache.
  • Feeling very tired or weak.
  • Swelling.
  • Change in skin color to black or purple.
  • Death of skin tissue may rarely happen. This can lead to loss of the body part (amputation) and can be deadly. Call your doctor right away if you have pain, color, or temperature change in any part of the body.
  • If you have kidney problems or have had kidney problems in the past, talk with your doctor. Kidney problems may happen. Call your doctor right away if you have signs of kidney problems like not able to pass urine, change in how much urine is passed, blood in the urine, or a big weight gain.

What are some other side effects of Jantoven?

All drugs may cause side effects. However, many people have no side effects or only have minor side effects. Call your doctor or get medical help if you have any side effects that bother you or do not go away.

These are not all of the side effects that may occur. If you have questions about side effects, call your doctor. Call your doctor for medical advice about side effects.

You may report side effects to the FDA at 1-800-332-1088. You may also report side effects at

If OVERDOSE is suspected:

If you think there has been an overdose, call your poison control center or get medical care right away. Be ready to tell or show what was taken, how much, and when it happened.

How do I store and/or throw out Jantoven?

  • Store at room temperature protected from light. Store in a dry place. Do not store in a bathroom.
  • Keep all drugs in a safe place. Keep all drugs out of the reach of children and pets.
  • Throw away unused or expired drugs. Do not flush down a toilet or pour down a drain unless you are told to do so. Check with your pharmacist if you have questions about the best way to throw out drugs. There may be drug take-back programs in your area.

Consumer information use

  • If your symptoms or health problems do not get better or if they become worse, call your doctor.
  • Do not share your drugs with others and do not take anyone else's drugs.
  • This medicine comes with an extra patient fact sheet called a Medication Guide. Read it with care. Read it again each time Jantoven (warfarin) is refilled. If you have any questions about Jantoven (warfarin), please talk with the doctor, pharmacist, or other health care provider.
  • If you think there has been an overdose, call your poison control center or get medical care right away. Be ready to tell or show what was taken, how much, and when it happened.

Further information

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