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Blood Clot Prevention: Coumadin® (warfarin)

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Your doctor has prescribed a medicine to prevent blood clots. The generic name for this medicine is warfarin. Coumadin® (COO-ma-din) is the name of the first brand of warfarin that was available. In this sheet, the name “Coumadin®” will be used because that is the name that many patients are most likely to hear. Warfarin and Coumadin® are the same medicine. All of this information applies to warfarin and to Coumadin®.

Coumadin® is an anticoagulant (an-tih-ko-AG-you-lent). Coumadin® is also referred to as a blood thinner. While it does not actually thin your blood, it will prevent blood clots from forming in the blood vessels. If you already have a blood clot, Coumadin® helps to keep the blood clot from getting larger and will protect you from forming new clots.

Your doctor may also prescribe Coumadin® even if you don’t currently have a blood clot. This is to protect you from developing blood clots if you have certain medical conditions.

Taking your medicine

It is very important to follow the instructions for your anticoagulant. Coumadin® is a medication that you take by mouth once a day. You should try to take your Coumadin® at the same time every day, preferably in the evening.

Your doctor will prescribe the dose of Coumadin® that is best for you. Coumadin® tablets are made in several strengths. Each tablet strength comes in a different color. This is called “color coding.” Several companies make generic warfarin tablets, but some use different color codes and often different shapes.

Do not rely on the color of your tablet to check the dose strength. Always check the dosage numbers on the tablet or the strength listed on the bottle. If your medicine looks different from what you had before or you are in doubt about the strength of your Coumadin® tablets, ask your pharmacist.

While you take Coumadin®, your doctor will order a blood test called PT/INR to see how long it takes your blood to clot. “PT” stands for protime. “INR” stands for international normalized ratio. The test results show if your dose needs to be adjusted. If your dose must be changed, your doctor or health care provider will call you and tell you the new dose to take.

It is very important that you keep all your appointments for blood tests and follow-up visits with your doctor. Your doctor will decide how long you need to take your anticoagulant.

If you miss a dose

If you miss a dose of Coumadin®, take the missed dose as soon as possible on the same day. Do not take a double dose the next day to make up for a missed dose. Call your health care provider any time you have missed a dose.


You will be able to do most of your normal activities while taking this medicine. You need to follow some precautions.

  • If possible, use an electric shaver instead of a blade razor when you shave.
  • Do not engage in contact sports.
  • Do not drink alcohol while taking anticoagulants.
  • Avoid drinking cranberry juice or eating cranberry products.
  • Anticoagulants may be dangerous in pregnancy. Call your doctor immediately if you are pregnant or think you may be pregnant. If you plan to become pregnant, discuss this with your doctor or health care provider first.

Be careful about medicines

  • Tell all of your doctors and dentists at all of your appointments that you are taking an anticoagulant.
  • Make sure to review your medicine list with your doctor or health care provider when you start an anticoagulant. Some medicines may keep your anticoagulant from working well.
  • Do not take any aspirin or aspirin products unless your doctor tells you that you may.
  • Do not take any over-the-counter medicines until you check with your doctor or health care provider. This includes over-the-counter cold and pain medicines, herbal products, vitamins, and supplements.
  • Carry a card in your purse or wallet that lists the medicines you take. Be sure to change the card when you stop taking a medicine, or get a new one.
  • Think about getting a medical alert bracelet that says you are taking Coumadin® or warfarin.

When to call the doctor

If you have any of the following, call your doctor or anticoagulation provider:

  • Bleeding of the gums or nose that does not stop within a couple of minutes
  • A wound that does not stop bleeding after pressure is applied
  • Blood in your urine or stool
  • Stools that are black or look like tar
  • Vomiting or coughing up blood
  • Bruises that appear for no reason, get larger or more painful, or are sudden or severe
  • Falling and hitting your head
  • Pain, swelling, redness, or warmth in your legs or arms
  • Shortness of breath
  • Chest pain or rapid heart beat
  • Feeling faint or weak
  • Pain, color, or temperature change in any area of the body

Pay attention to Vitamin K

Vitamin K from food and dietary supplements can interfere with the blood-thinning effects of Coumadin®. It is important to keep your intake of Vitamin K the same every day. Changing the amount of Vitamin K you get could result in bleeding or an unwanted blood clot.  

1.  Eat the same amount of high Vitamin K foods each day.

It is very important to be consistent. For instance, if you eat a half-cup of a high Vitamin K food daily, continue to eat this same amount each day.

High Vitamin K foods (listed with the highest first)

  • Broccoli
  • Brussels sprouts
  • Kale
  • Greens: collard, turnip, beet, mustard, dandelion
  • Green onions or scallions
  • Spinach

2.  Eat about the same amount of medium Vitamin K foods each day

For example, it would not be wise to eat leaf lettuce at every meal and then stop eating it entirely. It would be better to substitute another medium Vitamin K food from the list below for the leaf lettuce.

Medium Vitamin K foods (listed with the highest first)

  • Asparagus
  • Black-eyed peas
  • Cabbage or cole slaw
  • Okra
  • Prunes or dried plums
  • Dark green lettuce or salad greens, like Bibb, Boston, leaf lettuce, or endive
  • Parsley
  • Tofu

3.   Dietary Supplements

  • You may take a daily multivitamin. Many contain 25 micrograms of Vitamin K per tablet. If you do take a multivitamin supplement, you must take it every day.
  • Read the label of any dietary supplement. Do not take supplements that contain more than 100 micrograms of Vitamin K per day.
  • Avoid supplements that may affect how your blood clots. These include Vitamin E tablets, ginkgo, and garlic.