Normally, when an injury that causes
bleeding occurs, the body sends out signals that cause blood to clot at the
wound, and then the clot naturally breaks down as the wound heals. A person prone to
abnormal clotting has an imbalance between clot formation and clot breakdown.
Warfarin prevents new clots from forming and
prevents existing clots from growing by stopping the production of certain
proteins that are needed for blood to clot. Warfarin does not break up or dissolve
existing blood clots. Warfarin is a type of anticoagulant medicine.
If you have a high risk of these problems, such as having a recent surgery, you might take warfarin for a short time, about a few weeks.
If you have had deep vein thrombosis or pulmonary embolism, you might take warfarin for a longer time, such as 3 months or longer. The
length of time will vary based on your health.
How Well It Works
Warfarin reduces the chance that a
new blood clot will form or that an existing blood clot will get larger.
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
If you are pregnant, do not take warfarin. 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.