Warfarin Tablets

Warfarin is a blood thinner that comes in a tablet form. It prevents and treats blood clots. It can also lower your risk of a stroke if you have atrial fibrillation or heart valve replacement. The brand names of this medication are Coumadin® and Jantoven®.

What is this medication?

WARFARIN (WAR far in) prevents and treats blood clots. It may also be used to lower the risk of stroke in people with AFib (atrial fibrillation) or heart valve replacement. It belongs to a group of medications called blood thinners.

This medicine may be used for other purposes; ask your health care provider or pharmacist if you have questions.

COMMON BRAND NAME(S): Coumadin, Jantoven


Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy

What should I tell my care team before I take this medication?

They need to know if you have any of these conditions:

  • Alcoholism
  • Anemia
  • Bleeding disorders
  • Cancer
  • Diabetes
  • Heart disease
  • High blood pressure
  • History of bleeding in the gastrointestinal tract
  • History of stroke or other brain injury or disease
  • Kidney or liver disease
  • Protein C deficiency
  • Protein S deficiency
  • Psychosis or dementia
  • Recent injury, recent or planned surgery or procedure
  • An unusual or allergic reaction to warfarin, other medications, foods, dyes, or preservatives
  • Pregnant or trying to get pregnant
  • Breast-feeding

How should I use this medication?

Take this medication by mouth with a glass of water. Follow the directions on the prescription label. You can take this medication with or without food. Take your medication at the same time each day. Do not take it more often than directed. Do not stop taking except on your care team's advice. Stopping this medication may increase your risk of a blood clot. Be sure to refill your prescription before you run out of medication.

If your care team calls to change your dose, write down the dose and any other instructions. Always read the dose and instructions back to him or her to make sure you understand them. Tell your care team what strength of tablets you have on hand. Ask how many tablets you should take to equal your new dose. Write the date on the new instructions and keep them near your medication. If you are told to stop taking your medication until your next blood test, call your care team if you do not hear anything within 24 hours of the test to find out your new dose or when to restart your prior dose.

A special MedGuide will be given to you by the pharmacist with each prescription and refill. Be sure to read this information carefully each time.

Talk to your care team about the use of this medication in children. Special care may be needed.

Overdosage: If you think you have taken too much of this medicine contact a poison control center or emergency room at once.

NOTE: This medicine is only for you. Do not share this medicine with others.


What if I miss a dose?

It is important not to miss a dose. If you miss a dose, call your care team. Take the dose as soon as possible on the same day. If it is almost time for your next dose, take only that dose. Do not take double or extra doses to make up for a missed dose.

What may interact with this medication?

Do not take this medication with any of the following:

  • Defibrotide

This medication may also interact with the following:

  • Acyclovir
  • Allopurinol
  • Aprepitant
  • Armodafinil
  • Aspirin
  • Bicalutamide
  • Bosentan
  • Caffeine
  • Capecitabine
  • Certain antibiotics like erythromycin, clarithromycin, ciprofloxacin, cotrimoxazole, metronidazole, norfloxacin, or tigecycline
  • Certain antivirals for HIV or hepatitis
  • Certain medications for blood clots like argatroban, aspirin, bivalirudin, enoxaparin, fondaparinux, heparin, or lepirudin
  • Certain medications for blood pressure, heart disease, irregular heartbeat
  • Certain medications for cholesterol like atorvastatin, lovastatin, and simvastatin
  • Certain medications for depression, anxiety, or psychiatric disorders
  • Certain medications for fungal infections like fluconazole, ketoconazole, itraconazole, posaconazole, or voriconazole
  • Certain medications for seizures like carbamazepine, phenobarbital, phenytoin, rufinamide
  • Cilostazol
  • Clopidogrel
  • Conivaptan
  • Cyclosporine
  • Dipyridamole
  • Disulfiram
  • Female hormones, including contraceptive or birth control pills
  • Herbal or dietary products like garlic, ginkgo, ginseng, green tea, kava kava, red yeast rice, St. John's Wort
  • Isoniazid
  • Methoxsalen
  • Modafinil
  • Nilotinib
  • NSAIDs, medications for pain and inflammation, like ibuprofen or naproxen
  • Oxandrolone
  • Phenylpropanolamine
  • Prasugrel
  • Rifampin
  • Steroid medications like prednisone or cortisone
  • Stomach acid blockers like cimetidine, famotidine, ranitidine, or omeprazole
  • Sulfinpyrazone
  • Thiabendazole
  • Ticlopidine
  • Vitamin K
  • Zafirlukast
  • Zileuton

This list may not describe all possible interactions. Give your health care provider a list of all the medicines, herbs, non-prescription drugs, or dietary supplements you use. Also tell them if you smoke, drink alcohol, or use illegal drugs. Some items may interact with your medicine.


What should I watch for while using this medication?

Visit your care team for regular checks on your progress. You will need to have a blood test called a PT/INR regularly. The PT/INR blood test is done to make sure you are getting the right dose of this medication. It is important to not miss your appointment for the blood tests. When you first start taking this medication, these tests are done often. Once the correct dose is determined and you take your medication properly, these tests can be done less often.

Wear a medical ID bracelet or chain, and carry a card that describes your disease and details of your medication and dosage times.

Do not start taking or stop taking any medications or over-the-counter medications except on the advice of your care team.

You should discuss your diet with your care team. Do not make major changes in your diet. Vitamin K can affect how well this medication works. Many foods contain vitamin K. It is important to eat a consistent amount of foods with vitamin K. Other foods with vitamin K that you should eat in consistent amounts are asparagus, basil, black-eyed peas, broccoli, brussel sprouts, cabbage, green onions, green tea, parsley, green leafy vegetables like beet greens, collard greens, kale, spinach, turnip greens, or certain lettuces like green leaf or romaine.

This medication can cause birth defects or bleeding in an unborn child. Women of childbearing age should use effective birth control while taking this medication. If a woman becomes pregnant while taking this medication, she should discuss the potential risks and her options with her care team.

Avoid sports and activities that might cause injury while you are using this medication. Severe falls or injuries can cause unseen bleeding. Be careful when using sharp tools or knives. Consider using an electric razor. Take special care brushing or flossing your teeth. Report any injuries, bruising, or red spots on the skin to your care team.

If you have an illness that causes vomiting, diarrhea, or fever for more than a few days, contact your care team. Also, check with your care team if you are unable to eat for several days. These problems can change the effect of this medication.

Even after you stop taking this medication, it takes several days before your body recovers its normal ability to clot blood. Ask your care team how long you need to be careful. If you are going to have surgery or dental work, tell your care team that you have been taking this medication.

What side effects may I notice from receiving this medication?

Side effects that you should report to your care team as soon as possible:

  • Allergic reactions—skin rash, itching, hives, swelling of the face, lips, tongue, or throat
  • Bleeding—bloody or black, tar-like stools, vomiting blood or brown material that looks like coffee grounds, red or dark brown urine, small red or purple spots on skin, unusual bruising or bleeding
  • Bleeding in the brain—severe headache, stiff neck, confusion, dizziness, change in vision, numbness or weakness of the face, arm or leg, trouble speaking, trouble walking, vomiting
  • Dark or purple painful toes
  • Heavy periods
  • Painful swelling, warmth, or redness of the skin, blisters or sores

Side effects that usually do not require medical attention (report to your care team if they continue or are bothersome):

  • Diarrhea
  • Hair loss

This list may not describe all possible side effects. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

Where should I keep my medication?

Keep out of the reach of children and pets.

Store at room temperature between 15 and 30 degrees C (59 and 86 degrees F). Protect from light. Throw away any unused medication after the expiration date. Do not flush down the toilet.

NOTE: This sheet is a summary. It may not cover all possible information. If you have questions about this medicine, talk to your doctor, pharmacist, or health care provider.

Copyright ©2024 Elsevier Inc. All Rights Reserved.

Terms of use.

Note: Introduction and Additional Common Questions written and medically approved by Cleveland Clinic professionals.

Call Appointment Center 866.320.4573
Questions 216.444.2200