Warfarin (By mouth)


Warfarin (WAR-far-in)

Helps prevent or treat blood clots. May lower the risk of serious complications after a heart attack. This medicine is a blood thinner.

Brand Name(s)

Coumadin, Jantoven

When This Medicine Should Not Be Used

How to Use This Medicine


  • Take your medicine as directed. Your dose may need to be changed several times to find what works best for you.
  • This medicine should come with a Medication Guide. Ask your pharmacist for a copy if you do not have one.
  • Missed dose: Take a dose as soon as you remember. If it is almost time for your next dose, wait until then and take a regular dose. Do not take extra medicine to make up for a missed dose.
  • Store the medicine in a closed container at room temperature, away from heat, moisture, and direct light.

Drugs and Foods to Avoid

Ask your doctor or pharmacist before using any other medicine, including over-the-counter medicines, vitamins, and herbal products.

  • Many medicines and foods affect how warfarin works and affect your PT/INR results. Always tell your doctor before you start or stop any medicine. This includes vitamins, herbs, and supplements that you buy without a prescription, such as ginkgo, echinacea, and St John's wort. Keep a list of your medicines with you at all times.
  • Tell your doctor about all the medicines you are taking, including the following:
    • Medicine that thins your blood, such as Coumadin┬«, argatroban, aspirin, bivalirudin, cilostazol, clopidogrel, dabigatran, dipyridamole, desirudin, heparin, lepirudin, prasugrel, ticlopidine
    • NSAID pain or arthritis medicine, such as celecoxib, diclofenac, diflunisal, fenoprofen, ibuprofen, indomethacin, ketoprofen, ketorolac, mefenamic acid, naproxen, oxaprozin, piroxicam, sulindac
    • SSRI depression medicine, such as citalopram, desvenlafaxine, duloxetine, escitalopram, fluoxetine, fluvoxamine, milnacipran, paroxetine, sertraline, venlafaxine, vilazodone
  • Warfarin works best if you eat about the same amount of vitamin K every day. Foods high in vitamin K include asparagus, broccoli, brussels sprouts, cabbage, green leafy vegetables, plums, rhubarb, and vegetable oils such as canola oil. Talk to your doctor before you make big changes to the foods you eat.
  • Do not drink large amounts of cranberry juice or grapefruit juice. Ask your doctor how much juice is safe for you to have each day.

Warnings While Using This Medicine

  • It is not safe to take this medicine during pregnancy. It could harm an unborn baby. Tell your doctor right away if you become pregnant.
  • Tell your doctor if you are breastfeeding, or if you have any condition that may cause uncontrolled bleeding (such as a stomach ulcer or hemophilia). Tell your doctor if you have protein C deficiency, high blood pressure, diabetes, recent surgery or injury, or a history of stroke or problems caused by heparin. Tell your doctor if you have kidney, liver, or heart disease, cancer, or blood problems such as anemia.
  • You may bleed or bruise more easily while you are taking warfarin. The bleeding may become severe or life-threatening. To prevent injury or cuts, do not play rough sports, be careful with sharp objects, and brush and floss your teeth gently. Blow your nose gently. Do not pick your nose.
  • You must have a blood test such as a PT/INR to check how your blood is clotting. Your doctor may change the amount of warfarin you need based on your PT/INR results. You will be told how often to have the tests. Keep all appointments.
  • Check all medicine labels to make sure the medicine does not contain warfarin or an NSAID pain or arthritis medicine. You may develop serious bleeding problems if you take warfarin with an NSAID or if you take too much warfarin.
  • This medicine may cause the following serious problems:
    • Gangrene (skin or tissue damage)
    • Purple toes syndrome
  • Carry an ID card or wear a medical alert bracelet to let emergency caregivers know that you use warfarin.
  • Tell any doctor or dentist who treats you that you are using this medicine. You may need to stop using this medicine several days before you have surgery or medical tests.
  • Keep all medicine out of the reach of children. Never share your medicine with anyone.

Possible Side Effects While Using This Medicine

Call your doctor right away if you notice any of these side effects:

  • Allergic reaction: Itching or hives, swelling in your face or hands, swelling or tingling in your mouth or throat, chest tightness, trouble breathing
  • Bleeding that does not stop, bruising, or weakness
  • Bleeding from your gums or nose, coughing up blood, heavy menstrual bleeding
  • Dizziness, fainting, or lightheadedness
  • Numbness, tingling, or weakness anywhere in your body
  • Pain, brown or black skin, or skin that is cool to the touch
  • Purple discoloration of your toes or the soles of your feet, or new pain in a leg, foot, or your toes
  • Red or dark brown urine, or red or black stools
  • Vomiting blood or material that looks like coffee grounds
  • Yellow skin or the whites of your eyes

If you notice other side effects that you think are caused by this medicine, tell your doctor

Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088

Version Info

  • Last reviewed on 8/4/2014

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