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. Making your blood less likely to form dangerous clots and keeps clots you have from getting bigger. Warfarin does not break up clots you already have.

How do I take warfarin?

You can get warfarin as a generic or brand name (Coumadin®) tablet taken by mouth. Your health-care provider will figure out the amount you need to take by testing your blood.

Here are some important things to know about taking your warfarin:

  • Take your warfarin at the same time every day. Usually this is in the evening.
  • Write down your current dose and whenever a change is made by your care 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 the next day after you missed a dose, do not take the dose that you missed. Instead, keep with your usual daily dose.
  • Unless told to do so, do not take extra warfarin in one day to make up for a missed dose.
  • Since missing a dose of warfarin can change your blood tests, it is important to record the date you missed the dose. Tell your health-care provider at your next visit.
  • If you miss warfarin doses for two or more days, call your health-care provider right away.

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 only need it for a few months.

You should never stop taking your medicine without talking to your doctor.

Last reviewed: 
August 2017

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