How warfarin works and how to take it

How does warfarin work?

Vitamin K is found naturally in foods. Your body needs vitamin K to make clotting factors in your liver. These clotting factors help blood to clot and stop bleeding under normal conditions. Warfarin blocks vitamin K from making these clotting factors. This lowers the number of clotting factors in your blood. This makes your blood less likely to form dangerous clots and keeps clots you have from getting bigger. Warfarin does not break up a clot that has already formed.

How do I take warfarin?

Warfarin comes as a tablet. You take it by mouth. Your provider will figure out the amount you need to take by testing your blood.

When taking warfarin:

  • Take it at the same time each day. Most people take it in the evening.
  • Write down your current dose and when a change is made by your provider.
  • Use a pill box to organize your doses.
  • If you miss a dose, take the dose as soon as you can on the same day.
  • If you do not remember until more than 12 hours after you missed a dose, do not take the dose you missed. Instead, keep with your usual daily dose.
  • Unless told to do so, do not take extra warfarin in 1 day to make up for a missed dose.
  • Since missing a dose of warfarin can change your blood tests, record the date you missed the dose. Tell your provider at your next visit.
  • Call your provider right away if you miss warfarin doses for 2 or more days.

How long do I have to take warfarin?

The length of time you need to take warfarin will depend on the medical reason you take it. Some people have to take warfarin their whole life. Others need it for a few months.

Never stop taking your medicine without talking to your doctor.

How should I store warfarin?

Keep this medicine away from children. Store it at room temperature. Keep it away from too much heat and moisture, such as in the bathroom. Get rid of any medicine that is expired or no longer needed.

Last reviewed: 
December 2021

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