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What you need to know about Warfarin

(Coumadin® or Jantoven®)


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Warfarin (Coumadin or Jantoven) is a medicine used to prevent unwanted blood clots from forming. It is a type of medicine known as an anticoagulant (blood thinner). While often called a blood thinner, the blood does not truly get more thin.


Warfarin may be prescribed if you:

  • had a stroke caused by a blood clot
  • had a blood clot in your legs or lungs
  • have heart problems (such as abnormal heart rhythm, heart valve replacement or repair, heart failure or blocked arteries)
  • had surgery

What to tell your doctor

Tell your doctor before you start taking warfarin:

  • all prescription medicines you take
  • all over-the-counter medicines you take including:
    • aspirin
    • nonsteroidal anti-inflammatory medicines (ibuprofen: Advil®, Motrin® or naproxen: Aleve®)
    • acetaminophen (Tylenol®)
    • cold or cough medicine
    • antacids
    • heartburn relief (Tagamet®, cimetidine; Zantac®, ranitidine; or Prilosec®, omeprazole)
    • herbal supplements
    • vitamins and nutritional supplements
  • if you are pregnant, planning to become pregnant or are currently breastfeeding
  • your medical history

Your dose

Your doctor wants to make sure that the amount of warfarin in your blood is at a steady level to prevent clotting. This is done with a blood test called the INR (international normalized ratio) or CFX (chromogenic factor X).

Your warfarin dose will be adjusted to keep your INR/CFX at a goal range set by your doctor. Your goal INR/CFX will depend on your medical condition.

You will need to have your INR/CFX checked at least every month. You may need to have it checked more often when you first start taking warfarin, if your INR/CFX is not in the goal range, or if you have changes in your health, other medicines or diet.

Your INR/CFX goal is ______________________________________.

Your doctor, pharmacist or nurse will tell you when you need an INR/CFX test. Call the lab or INR/CFX clinic at the phone number given to you to schedule the test.

It is important that you make and keep all of your INR/CFX appointments. Your doctor may need to change your warfarin dose to keep your INR/CFX within a goal range.

Keep a record of your INR/CFX test results and your dosage changes. Use the dosage calendars in this booklet.

Side effects of warfarin

Side effects of warfarin include:

  • nosebleeds
  • bleeding from the gums when you brush your teeth
  • bleeding from cuts or other breaks in your skin
  • increased bruising
  • increased menstrual flow
  • blood in your stool or urine

How to take warfarin

  • Take warfarin as directed.
  • Take your dose every day at the same time.
  • If you miss a dose, take it as soon as you can. Do not add it to your next dose. Instead, call your doctor, who may want to adjust your next dose.
    If you have an INR/CFX test scheduled in the next few days, call your doctor or clinic to see if you should re-schedule.
  • Do not stop taking warfarin without talking to your doctor.
  • Do not take warfarin if you are pregnant, may become pregnant or if you are breastfeeding. Warfarin may be harmful to unborn babies and infants.

How to store warfarin

  • Keep warfarin in its original container. Keep it away from heat, light and humidity. Do not store it in the bathroom or near the kitchen sink.
  • Try to refill all of your prescriptions at the same pharmacy. Your pharmacist will have a record of all of your medicines and can tell you if your medicines will interact or interfere with each other.

What to expect after stopping warfarin

If your doctor tells you to stop taking warfarin, you can expect its effects to last up to five days after you stop taking it. Keep following bleeding precautions during this time.

Using other medicines with warfarin

Some medicines may interact with warfarin to cause side effects or interfere with how well the warfarin works. Tell each of your health care providers when you start, stop or change the doses of herbal products and other medicines you take.

  • When using any over-the-counter product, read the ingredients label. Do not use aspirin and products that contain aspirin or acetylsalicylic acid (another name for aspirin) without talking with your doctor.
    • Aspirin can increase the effects of warfarin or can irritate your stomach lining and cause bleeding.
    • Check the ingredients of generic products for aspirin or acetylsalicylic acid.
  • Common brand name products that contain aspirin are:
    • Alka Seltzer®
    • Anacin®
    • Ascriptin®
    • Aspergum®
    • Bufferin®
    • Excedrin®
    • Pepto Bismol®
  • Avoid using nonsteroidal anti-inflammatory medicines, unless your doctor tells you it is OK. Common products are:
    • ibuprofen (such as Advil®, Motrin®, Nuprin®)
    • naproxen (such as Aleve®, Naprosyn®)
    • ketoprofen (Orudis®)
  • You may use acetaminophen (Tylenol®) once in a while for headaches, muscle aches or fever. If you regularly take doses for several days, it may affect your INR/CFX results. Talk with your doctor if you need regular use of acetaminophen for any symptoms.
  • Ask your doctor or pharmacist for suggested medicines for colds or allergies. Products that may be safe to use include do not include aspirin or acetylsalicylic acid but may include ingredients such as:
    • acetaminophen
    • chlorpheniramine
    • dextromethorphan
    • diphenhydramine
    • phenylephrine
    • pseudoephedrine
  •  Take these medicines for heartburn at least two hours before or after you take your warfarin dose:
    • aluminum hydroxide and magnesium hydroxide (such as Maalox®)
    • aluminum hydroxide and simethicone (such as Mylanta®).

Vitamin E

High doses of vitamin E — received only through a supplement — have been shown to increase the risk of bleeding. Talk with your doctor before taking any vitamin E supplements.

Fish oil supplements

Omega-3 fatty acids supplements may increase the anticoagulant effect of warfarin. This means they may slow blood clotting. Omega-3 fatty acid supplements may be used in consistent amounts. Talk with your doctor before taking omega-3 fatty acid supplements.

Vitamins, herbs and other nutritional supplements

There are many medicines, vitamins, herbs and nutritional supplements that can change how well warfarin works in your body. Talk with your doctor before you make any changes to your medicines.

Call your doctor if you are currently taking, or are thinking about taking, any of the following (not a complete list):

  • ginseng
  • coenzyme Q10
  • feverfew
  • papain
  • dong quai
  • devil’s claw
  • St. John’s wort
  • danshen
  • seaweed
  • Viactiv ™ calcium supplements
  • salvia root
  • gingko biloba
  • garlic (in large amounts)
  • kava
  • ginger
  • home brewed teas with tonka beans, melilot (sweet clover) or sweet woodruff
  • multivitamins with vitamin K
  • any other supplements not on this list

Information about herbal products is always changing. Important: talk with your doctor about any herbal product or dietary supplement you are taking or thinking about taking. Your doctor can tell you if the supplement may interact with your medicine(s).

Vitamin K

There are many foods that can change how warfarin works in your body, especially those that have high amounts of vitamin K. Warfarin and vitamin K work against each other. Warfarin slows down blood clotting and vitamin K helps blood to clot. 

  • The highest sources of vitamin K include:
    • broccoli
    • brussels sprouts
    • cabbage
    • collard greens
    • endive
    • green onions
    • kale (raw leaf)
    • lettuce (Bibb, Romaine, red leaf or other dark, leafy lettuces)
    • spinach
    • Swiss chard
    • turnip greens
    • watercress
  • Limit these foods to small amounts if you do not normally eat them. 
  • If you do normally eat these foods, do not change the amount you eat.
  • One serving size is one-half to one cup.
  • If you want to make a major change in your diet, talk with your doctor. You may need to have your INR/CFX tested more often for a while.
  • Canola, olive and soybean oils are high in vitamin K. Limit them to two tablespoons each day.
  • Green tea has high levels of vitamin K. If you drink green tea, be consistent with how much you drink each day.
  • A dietitian can help you choose foods to keep your INR/CFX stable.


      Alcohol may change the effects of warfarin. Remember, have no more than one alcoholic beverage a day. One drink equals:

      • 12 ounces beer
      • four ounces wine
      • one ounce hard liquor

      Cranberry juice

      There have been reports that cranberry juice may affect the anticoagulant effects of warfarin. Talk with your doctor before adding cranberry juice to your diet or if you regularly drink cranberry juice.

      Tobacco use

      You should not use tobacco products while you are taking warfarin. Smoking can affect your INR/CFX levels. Chewing tobacco has high levels of vitamin K and can affect the action of warfarin.

      All tobacco use increases your chances for a variety of cancer and heart-related illnesses. If you are ready to quit, please talk with your doctor. If you can't quit, keep your use consistent and try to cut down.

      Traveling with warfarin

      • Tell your doctor when you plan to travel. You may need an INR/CFX test before you leave. Your doctor will tell you if you will need to take a test while traveling. Bring this booklet on your trip so you can fill in your dosage chart.
      • Fill your prescription ahead of time and bring it with you so you do not run out of warfarin.
      • Keep your medicines with you in a purse or carry-on bag instead of your luggage. If your luggage becomes lost, you will still have your medicines.
      • Remember to keep to your everyday diet and exercise routines.
      • Try to take warfarin at the same time each day. If you are traveling across time zones, ask your doctor when you should take your daily dose.
      • If you need medical or dental services while traveling, be sure to tell the doctor or dentist you take warfarin.


      If an illness keeps you from eating your normal diet, call your doctor. Vomiting and diarrhea can decrease your body's supply of vitamin K and cause your INR/CFX level to rise. This can lead to bleeding.

      Fever and infection can also affect how well the warfarin works. You may need to have more blood tests while you are ill and while you recover.

      Physical activity

      Talk with your doctor about which sports or physical activities will be safe for you. In general, avoid sports or activities that may result in a fall or injury. Your doctor may give you activity restrictions or talk with you about adapting a current sport or activity so it is safe for you.

      Wear a helmet while doing activities that increase your risk for a head injury, such as inline skating, biking or motorcycle riding. Please follow your doctor’s orders.


      • Be extra careful to avoid injuries while taking warfarin. You could bleed more easily from cuts or wounds. Use caution around sharp objects. Use an electric razor. Be especially careful when working with knives and scissors.
      • Wear slippers or shoes at all times, even in the house.
      • Trim your nails carefully. Trim them straight across with a nail clippers. Do not pick at the cuticle.
      • Use a soft toothbrush. Gently brush and floss your teeth.
      • Avoid activities that may increase your risk for injury, such as hunting and contact sports.
      • Tell your dentist, doctors and other health care providers you take warfarin before planning any dental work or medical surgery or procedure.

        Your doctor will tell you if you need to stop taking warfarin and when to resume taking it. He or she may also want you to take another anticoagulant to reduce the risk of blood clots while you are not taking warfarin.
      • Consider wearing an identification necklace or bracelet that says you take anticoagulant medicine. Ask your nurse or doctor for an identification card you can keep in a purse or wallet.

      Who else needs to know you take warfarin

      Tell your dentist, doctors and other health care providers you take warfarin before planning any dental work, surgery or procedure.

      When to call your doctor

      Call your doctor if you have:

      • unusual, unexplained or large areas of bruising
      • increased bruising
      • spitting or coughing up blood
      • pink, red or dark brown urine
      • red or tarry black stools
      • bleeding from cuts or other breaks in your skin that continues after applying pressure to the area for five minutes
      • nosebleeds that last longer than five minutes or that occur three or more times a week
      • bleeding from your gums when brushing your teeth
      • dizziness or weakness
      • unusually heavy or long menstrual periods
      • headaches that don’t go away with medicine, rest or both
      • swelling or pain anywhere (with or without bruising)
      • any blow to your head or abdomen (belly) that may cause internal bleeding

        When to call 911

        Call 911 or have someone take you to a hospital Emergency Department if you have:

        • symptoms of stroke:
          • sudden or temporary weakness
          • numbness or paralysis in an arm, hand, leg or facial muscles (usually on one side of the body)
          • sudden blurred double vision or dimness in your eye(s)
          • sudden confusion
          • trouble speaking or understanding language, or thinking
          • sudden clumsiness
          • loss of balance
          • dizziness
          • sudden severe headache
        • other emergency

        Content Source: What You Need To Know About Warfarin (Coumadin®) med-ahc-21924
        Review Date: 12/1/2017
        Reviewed By: Allina Health Patient Education experts

        The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed medical professional should be consulted for diagnosis and treatment of any and all medical conditions. Call 9-1-1 for all medical emergencies. Links to other sites are provided for information only—they do not constitute endorsements of those other sites.