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Warfarin: Taking Your Medicine Safely


Warfarin is a medicine that helps prevent blood clots. It is often called a blood thinner. Doctors give warfarin to reduce the risk of blood clots.

Warfarin slows the time it takes for your blood to clot. That means it can cause bleeding problems. So it's important to know how to take it safely.

Foods and other medicines can affect the way warfarin works. Some can make warfarin work too well, which can cause bleeding. Others can make it work poorly, so that it doesn't prevent clots very well.

You'll also need regular blood tests to check how long it takes for your blood to form a clot. Depending on the results, your doctor may adjust your dose of warfarin.

How do you take warfarin safely?

These steps can help you take warfarin safely.

  • Follow the instructions for taking warfarin properly.
    • Take your medicine at the same time each day.
    • If you miss a dose, don't take an extra dose to make up for it. Your doctor can tell you exactly what to do so you don't take too much or too little.
  • Get regular blood tests.

    The test results tell your doctor whether your dose needs to be changed. Do not change your dose unless your doctor tells you to.

  • Prevent falls and injuries.

    For example:

    • Wear slippers or shoes with non-skid soles.
    • Remove throw rugs and clutter.
    • Rearrange furniture and electrical cords to keep them out of walking paths.
    • Keep stairways, porches, and outside walkways well lit. Use night-lights in hallways and bathrooms.
    • Be extra careful when you work with sharp tools or knives.
  • Be careful with other medicines.

    Many medicines can affect how warfarin works.

    • Tell all of your doctors, dentists, and pharmacists that you take warfarin.
    • Give your list of medicines to every doctor and dentist who treats you. Include all of the prescription medicines, over-the-counter medicines, antibiotics, and natural health products that you take.
    • Talk to your doctor before you start or stop taking any medicines or natural health products.
  • Don't smoke.

    Smoking affects how the body uses medicine, and it increases the blood's clotting effects.

  • Eat a similar amount of vitamin K every day.
    • Do not suddenly eat a lot more or a lot less food that is rich in vitamin K than you usually do. Vitamin K affects how warfarin works and how your blood clots.
    • Foods that have a lot of vitamin K include cooked green vegetables, such as:
      • Kale, spinach, turnip greens, collard greens, Swiss chard, and mustard greens.
      • Brussels sprouts, broccoli, and cabbage.
  • Talk with your doctor before making big changes in your diet.
    • Check with your doctor before you start a diet to lose weight.
    • Check with your doctor before you take any natural health products. Some may contain vitamin K.
  • Limit alcohol.

    It can change how warfarin works.

  • Wear medical alert jewellery.

    These are bracelets, pendants, or charms that let others know you take warfarin.

  • Don't take warfarin if you are pregnant or planning to get pregnant.

    Talk to your doctor about how you can prevent getting pregnant while you are taking it. If you think you might be pregnant, call your doctor.

  • Know when to get help for signs of bleeding.

    Call 911 or other emergency services right away if:

    • You have a sudden, severe headache that is different from past headaches.
    • You cough up blood.
    • You vomit blood or what looks like coffee grounds.
    • Your stools are maroon or very bloody.

    Call your doctor now or seek medical care right away if:

    • You have new bruises or blood spots under your skin.
    • You have a nosebleed.
    • Your gums bleed when you brush your teeth.
    • You have blood in your urine.
    • Your stools are black.
    • You have blood in your stools.
    • You have vaginal bleeding that is different (heavier, more frequent, at a different time of the month) than what you are used to.


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