Warfarin helps prevent the
formation of blood clots by increasing the time it takes a blood clot to form.
This also prevents an existing clot from getting larger.
Why It Is Used
Warfarin is used to lower the
risk of stroke in people who have
atrial fibrillation. Your doctor may recommend
warfarin based on your risk factors and on whether you can take
warfarin safely. Anything that increases your risk for a disease or
problem is called a risk factor. The more risk factors you have, the greater
your risk of stroke.
Warfarin can reduce the risk of stroke in anyone who has
atrial fibrillation. Even after your heart rhythm is under control, you may
still take warfarin. Some people go in and out of atrial fibrillation without
even knowing it. Taking warfarin can lower your chances of having a blood clot
or a stroke.
Your doctor may have you take an anticoagulant for a few
weeks after cardioversion for atrial fibrillation.
How Well It Works
Warfarin lowers the risk of stroke in people
who have atrial fibrillation. But how much your risk
will be lowered depends on how high your risk was to start with. Not everyone
with atrial fibrillation has the same risk of stroke. It's a good idea to talk
with your doctor about your risk.
You will want to weigh the
benefits of reducing your risk of stroke against the risks of taking
warfarin. Warfarin works well to prevent stroke. But warfarin also
raises the risk of bleeding. Each year 1 to 2 out of 100 people who take
warfarin will have a problem with severe bleeding, and 98 to 99 will not.1 But this is an average risk. Your own risk may be higher or
lower than average, based on your own health.
All medicines have side effects. But many people don't feel the side effects, or they are able to deal with them. Ask your pharmacist about the side effects of each medicine you take. Side effects are also listed in the information that comes with your medicine.
Here are some important things to think about:
Usually the benefits of the medicine are more important than any minor side effects.
Side effects may go away after you take the medicine for a while.
If side effects still bother you and you wonder if you should keep taking the medicine, call your doctor. He or she may be able to lower your dose or change your medicine. Do not suddenly quit taking your medicine unless your doctor tells you to.
Bleeding: Call 911 or other emergency services right away if:
You cough up blood.
You vomit blood or what looks like coffee grounds.
You pass maroon or very bloody stools.
You have a sudden, severe headache that is different from past headaches. (It may be a sign of bleeding in the brain.)
Call your doctor right away if:
You have new bruises or blood spots under your skin.
You have a nosebleed that doesn't stop quickly.
Your gums bleed when you brush your teeth.
You have blood in your urine.
Your stools are black and look like tar or have streaks of blood.
You have heavy period bleeding or vaginal bleeding when you are not having your period.
If you are injured, apply pressure to stop the bleeding. Realize that it
will take longer than you are used to for the bleeding to stop. If you can't get the bleeding to stop, call your doctor.
Allergic reaction: Call 911 or other emergency services right away if you have:
Swelling of your face, lips, tongue, or throat.
Call your doctor if you have:
Other side effects of warfarin include:
See Drug Reference for a full list of side effects. (Drug
Reference is not available in all systems.)
What To Think About
When you take warfarin, you need to take extra steps to avoid bleeding problems.
Get regular blood tests.
Prevent falls and injuries.
Eat a steady diet, and pay attention to foods that contain vitamin K.
Tell your doctors about all other medicines and vitamins that you take.
Medicine is one of the many tools your doctor has to treat a health problem. Taking medicine as your doctor suggests will improve your health and may prevent future problems. If you don't take your medicines properly, you may be putting your health (and perhaps your life) at risk.
There are many reasons why people have trouble taking their medicine. But in most cases, there is something you can do. For suggestions on how to work around common problems, see the topic Taking Medicines as Prescribed.
Advice for women
Do not take warfarin if you are pregnant. Warfarin can cause miscarriage or birth defects. If you are taking warfarin, talk to your doctor about how you can prevent pregnancy.
If you think you might be pregnant: Call your doctor. If you are pregnant, you will take heparin during your pregnancy.
If you plan on getting pregnant: Talk with your doctor. You and your doctor will decide which medicine you will take—warfarin or heparin—while trying to get pregnant.
Follow-up care is a key part of your treatment and safety. Be sure to make and go to all appointments, and call your doctor if you are having problems. It's also a good idea to know your test results and keep a list of the medicines you take.
Antithrombotic drugs (2011). Treatment Guidelines From The Medical Letter, 9(110): 61–66.
How this information was developed to help you make better health decisions.