Warfarin (Coumadin®)

(complete brochure)


What is Warfarin?

Warfarin (Coumadin©) is an anticoagulant (blood thinner) that will slow down blood clotting to an extent that prevents abnormal blood clots from developing or worsening.


Why is Warfarin used?

  • To prevent an abnormal blood clot from developing
  • To treat an abnormal blood clot in the legs or lung
  • To prevent clots from developing around your mechanical heart valve or heart


What dose of Warfarin will be prescribed?

  • Your Warfarin dose may be managed by your doctor, a pharmacist, nurse practitioner or a local anticoagulation clinic. In this document, we will refer to the person who is helping you manage your warfarin therapy as your health care provider.
  • A blood test called an INR is required to ensure your Warfarin is working safely and effectively. An INR is required frequently at the start of therapy and will be become less frequent once your regular warfarin dose has been found. It should typically be done no more often than once per week unless there are unusual circumstances.
  • If you are not taking Warfarin your INR is around 1.0 (0.9-1.2).
  • Your Warfarin dose may change from time to time depending on your on INR.
  • Keep a record of every INR result and warfarin dose that you have taken. Write down all Warfarin doses and the date of the next INR test.


How should warfarin be taken?

  • Warfarin should be taken around the same time every day. It may be taken with food or on an empty stomach and may be taken with other medications; in other words, warfarin does NOT need its own administration time.
  • The amount of warfarin that each person needs is different. Changes to your dose, based on your blood test, are sometimes needed.
  • Warfarin will come in different colours; each colour represents a different dose.

  • Depending on your dose you may need to break the tablets into halves. A pill cutter is recommended.
  • If you take a half of a tablet; take the other half the next day.
  • If you miss a dose, take it if you remember it later that day. If you don’t remember it until the next day, skip it.
  • If you have missed more than 2 doses, inform your health care provider as many missed doses may affect your INR.
  • Check your tablet color before leaving the pharmacy. If your tablets look different than usual, talk to the pharmacist.


What can change the effect of Warfarin?


D – Diet changes – green vegetables can affect your INR – but don’t stop eating them. Just try to eat the same amount every week.

  • Alcohol – one or two alcoholic drinks a day is ok, but do not binge drink

I – Illness – if you get sick with a cold, flu, nausea, vomiting or diarrhea, or any other illness, it may affect your INR. Call your doctor if you have stomach problems, vomiting or diarrhea for more than one day as this could affect your INR.

M – Medications – any change in medications, including dose changes may affect your INR. This includes prescription medicines, over-the counter medicines, vitamins, and herbal products. Be sure your health care provider is aware that you are taking warfarin. If you have any medication changes, including dose changes or starting antibiotics, check your INR within 3 days. Any product containing Aspirin or medicines similar to Aspirin may be harmful when taking warfarin, as it can increase the risk of bleeding.

  • Any product containing Aspirin or medicines similar to Aspirin may be harmful when taking Warfarin as it can increase the risk of bleeding
  • Avoid over the counter pain relievers until you have discussed whether it is safe to use them with your doctor.

E – Error (missed dose) – if you miss a dose it may affect your INR. If you miss a dose, take the missed dose as soon as you remember. Do NOT take a double dose the next day to make up for the missed dose

Keep record of your INR and Warfarin. Include date, warfarin dose, any changes in DIME (Diet, Illness, Medications, or Error (missed doses)). Provide your health care provider with this information and to let them know you have had an INR test drawn. Write down any warfarin dose changes and the date of next INR provided to you by your health care provider.


Are there side effects?

  • If your INR is above your target you have an increased chance of bleeding
  • If your INR is below your target, you have an increased chance of developing a clot

The major side effect of warfarin is bleeding

  • Warfarin does not make you bleed but will make any source of bleeding bleed more. It is important to monitor your INR level so it is in the right range for you.
  • If you become pregnant, or if you plan to become pregnant while taking Warfarin, contact your health care provider:
  • Slight Bleeding:
    • Nose bleeds and gum bleeds
    • If your nose starts bleeding, pinch and hold tightly for 10 minutes without stopping. If still bleeding, pinch and hold for another 10 minutes. If still bleeding, contact your health care provider or go to a health clinic or emergency room
    • A soft toothbrush may help decrease bleeding of the gums
  • Easy bruising
  • Bleeding after a cut that take a little longer to stop
  • Do not stop taking warfarin if you experience minor bleeding
  • Major bleeding:
    • Red, dark or coffee coloured urine
    • Red or black bowel movements
    • Coughing or vomiting bright red blood or “coffee grounds”
    • A cut that does not stop after 10 minutes of pressure
    • A serious fall or hit to the head
    • A severe headache with nausea or vomiting


Tips to reduce your chances of bleeding

Exercise is important to staying healthy. Continue your regular exercise but remember that when you are taking warfarin your risk of bleeding with injury is higher.

  • Be sure to wear appropriate protective gear and receive appropriate training with sports (i.e. helmet with biking).
  • Use your common sense. Do not do dangerous activities like extreme sports.
  • You may have your immunizations and flu shots – apply pressure for 10 minutes after the injection site to decrease bruising.
  • Wear a medical alert bracelet.


Take Away Message

  • Take your Warfarin around the same time very day.
  • Regular blood testing (INR) in important to keep you safe on Warfarin.
  • Major changes in DIME (Diet, Illness, Medications, or Error (missed doses)).
  • Warfarin will make any source of bleeding worse.
  • Contact your health care provider if you become pregnant on Warfarin.
  • Continue healthy exercise – but be safe in doing so!



The above information was directly obtained from the Thrombosis Canada website (thrombosiscanada.ca).


Did you know?

H1 Icon

Did you know that certain oral anticoagulants (blood thinners) don’t require regular blood tests and can be taken instead of warfarin (Coumadin) in patients with:


-Deep Vein Thrombosis or Pulmonary Embolism

-Atrial Fibrillation in patients who never had a  heart valve replacement

Did you know that there is an information video playing in CETAC about warfarin (Coumadin) that can also be viewed on this website?

Did you know that our Anticoagulation and Thrombosis clinic is now called CETAC ? It stands for  “Centre of Excellence in Thrombosis and Anticoagulation.”

Did you know that CETAC is heavily involved in research to advance the care and lifestyle of our patients? You can look on this website to see what studies we are doing and if you are a potential participant.