Warfarin may cause severe bleeding that can be life-threatening and even cause death. Tell your doctor if you have or have ever had a blood or bleeding disorder; bleeding problems, especially in your stomach or your esophagus (tube from the throat to the stomach), intestines, urinary tract or bladder, or lungs; high blood pressure; heart attack; angina (chest pain or pressure); heart disease; pericarditis (swelling of the lining (sac) around the heart); endocarditis (infection of one or more heart valves); a stroke or ministroke; aneurysm (weakening or tearing of an artery or vein); anemia (low number of red blood cells in the blood); cancer; chronic diarrhea; or kidney, or liver disease. Also tell your doctor if you fall often or have had a recent serious injury or surgery. Bleeding is more likely during warfarin treatment for people over 65 years of age, and it is also more likely during the first few weeks of warfarin treatment. Bleeding is also more likely to occur for people who take high doses of warfarin, or take this medication for a long time. The risk for bleeding while taking warfarin is also higher for people participating in an activity or sport that may result in serious injury. Tell your doctor and pharmacist if you are taking or plan to take any prescription or nonprescription medications, vitamins, nutritional supplements, and herbal or botanical products (See SPECIAL PRECAUTIONS), as some of these products may increase the risk for bleeding while you are taking warfarin. If you experience any of the following symptoms, call your doctor immediately: pain, swelling, or discomfort, bleeding from a cut that does not stop in the usual amount of time, nosebleeds or bleeding from your gums, coughing up or vomiting blood or material that looks like coffee grounds, unusual bleeding or bruising, increased menstrual flow or vaginal bleeding, pink, red, or dark brown urine, red or tarry black bowel movements, headache, dizziness, or weakness.
Some people may respond differently to warfarin based on their heredity or genetic make-up. Your doctor may order a blood test to help find the dose of warfarin that is best for you. Keep all appointments with your doctor and the laboratory. Your doctor will order certain tests to check your body's response to warfarin.
Warfarin prevents blood from clotting so it may take longer than usual for you to stop bleeding if you are cut or injured. Avoid activities or sports that have a high risk of causing injury. Call your doctor if bleeding is unusual or if you fall and get hurt, especially if you hit your head.
If your doctor tells you to stop taking warfarin, the effects of this medication may last for 2 to 5 days after you stop taking it.
Your doctor or pharmacist will give you the manufacturer's patient information sheet (Medication Guide) when you begin treatment with warfarin and each time you refill your prescription. Read the information carefully and ask your doctor or pharmacist if you have any questions. You can also visit the Food and Drug Administration (FDA) website ( Web Site) or the manufacturer's website to obtain the Medication Guide.
Talk to your doctor about the risk(s) of taking warfarin.
Warfarin is used to prevent blood clots from forming or growing larger in your blood and blood vessels. It is prescribed for people with certain types of irregular heartbeat, people with prosthetic (replacement or mechanical) heart valves, and people who have suffered a heart attack. Warfarin is also used to treat or prevent venous thrombosis (swelling and blood clot in a vein) and pulmonary embolism (a blood clot in the lung). Warfarin is in a class of medications called anticoagulants ('blood thinners'). It works by decreasing the clotting ability of the blood.
Warfarin comes as a tablet to take by mouth. It is usually taken once a day with or without food. Take warfarin at around the same time every day. Follow the directions on your prescription label carefully, and ask your doctor or pharmacist to explain any part you do not understand. Take warfarin exactly as directed. Do not take more or less of it or take it more often than prescribed by your doctor. Call your doctor immediately if you take more than your prescribed dose of warfarin.
Your doctor will probably start you on a low dose of warfarin and gradually increase or decrease your dose based on the results of your blood tests. Make sure you understand any new dosing instructions from your doctor.
Continue to take warfarin even if you feel well. Do not stop taking warfarin without talking to your doctor.
This medication may be prescribed for other uses; ask your doctor or pharmacist for more information.
Before taking warfarin,
- tell your doctor and pharmacist if you are allergic to warfarin or any other medications.
- do not take two or more medications that contain warfarin at the same time. Be sure to check with your doctor or pharmacist if you are uncertain if a medication contains warfarin or warfarin sodium.
- tell your doctor and pharmacist what prescription and nonprescription medications, vitamins, and nutritional supplements you are taking or plan to take, especially antibiotics; aspirin or aspirin-containing products and other nonsteroidal anti-inflammatory drugs such as ibuprofen (Advil, Motrin) and naproxen (Aleve, Naprosyn); heparin; medications for cancer, cholesterol, colds and allergies, depression, diabetes, digestive problems (including ulcers and heartburn), gout, heart disease, mental illness, pain,seizures, thyroid problems, and tuberculosis; oral contraceptives (birth control pills); streptokinase; ticlopidine; or urokinase. Many other medications may also interact with warfarin, so be sure to tell your doctor about all the medications you are taking, even those that do not appear on this list. Do not take any new medications or stop taking any medication without talking to your doctor.
- tell your doctor and pharmacist what herbal or botanical products you are taking, especially bromelains, coenzyme Q10 (Ubidecarenone), cranberry products, danshen, dong quai, garlic, Ginkgo biloba, ginseng, and St. John's wort. There are many other herbal or botanical products which might affect your body's response to warfarin. Do not start or stop taking any herbal products without talking to your doctor.
- tell your doctor if you have or have ever had a thyroid condition or diabetes. Also tell your doctor if you have an infection, a gastrointestinal illness such as diarrhea, or sprue (an allergic reaction to protein found in grains that causes diarrhea), or an indwelling catheter (a flexible plastic tube that is placed into the bladder to allow the urine to drain out).
- Tell your doctor if you are pregnant, think you might be pregnant, or plan to become pregnant while taking warfarin. You should not take warfarin if you are pregnant. Talk to your doctor about the use of effective birth control while taking warfarin. If you become pregnant while taking warfarin, call your doctor immediately. Warfarin may harm the fetus.
- tell your doctor if you are breast-feeding.
- if you are having surgery, including dental surgery, or any type of medical or dental procedure, tell the doctor or dentist that you are taking warfarin. Your doctor may tell you to stop taking warfarin before the surgery or procedure or change your dosage of warfarin before the surgery or procedure. Follow your doctor's directions carefully and keep all appointments with the laboratory if your doctor orders blood tests to find the best dose of warfarin for you.
- tell your doctor if you drink or have ever drunk large amounts of alcohol. Your doctor will probably tell you not to take warfarin. Avoid drinking alcohol while you are taking this medication.
- If you are going to receive an immunization, such as a flu shot, or any other injection into a muscle, tell the health care professional that you are taking warfarin.
Eat a normal, healthy diet with the same amount of foods that contain vitamin K; ask your doctor or pharmacist for a list of foods that contain vitamin K. Be sure to talk to your doctor before you make any changes in your diet or try to gain or lose weight. Do not eat large amounts of leafy, green vegetables or certain vegetable oils, such as soybean or canola, that contain large amounts of vitamin K. Avoid juice or products that contain cranberries. Ask your doctor about eating licorice while taking warfarin.
Tell your doctor if you drink nutritional supplements or receive supplements by a feeding tube.
Take the missed dose as soon as you remember it, if it is the same day that you were to take the dose. Do not take a double dose the next day to make up for a missed one. Talk to your doctor if you miss a dose of warfarin.
Warfarin may cause side effects. Tell your doctor if any of these symptoms are severe or do not go away:
- change in the way things taste
- pale skin
- loss of hair
- feeling cold or having chills
If you experience any of the following symptoms, or those listed in the IMPORTANT WARNING section, call your doctor immediately:
- difficulty breathing or swallowing
- swelling of the face, throat, tongue, lips, or eyes
- chest pain or pressure
- swelling of the hands, feet, ankles, or lower legs
- loss of appetite
- pain in the upper right part of the stomach
- yellowing of the skin or eyes
- flu-like symptoms
- joint or muscle pain
- difficultly in moving any part of your body
- feelings of numbness, tingling, pricking, burning, or creeping on the skin
- painful erection of the penis that lasts for hours
You should know that warfarin may cause necrosis or gangrene (death of skin or other body tissues). Call your doctor immediately if you notice a purplish or darkened color to your skin, skin changes, ulcers, or an unusual problem in any area of your skin or body, or if you have a severe pain that occurs suddenly, or color or temperature change in any area of your body. Call your doctor immediately if your toes become painful or become purple or dark in color. You may need medical care right away to prevent amputation (removal) of your affected body part.
Warfarin may cause other side effects. Call your doctor if you have any unusual problems while taking this medication.
Keep this medication in the container it came in, tightly closed, and out of reach of children. Store it at room temperature and away from excess heat, moisture (not in the bathroom), and light. Throw away any medication that is outdated or no longer needed. Talk to your pharmacist about the proper disposal of your medication.
In case of overdose, call your local poison control center at 1-800-222-1222. If the victim has collapsed or is not breathing, call local emergency services at 911.
Symptoms of overdose may include:
- bloody or red, or tarry bowel movements
- spitting or coughing up blood
- heavy bleeding with your menstrual period
- pink, red, or dark brown urine
- coughing up or vomiting material that looks like coffee grounds
- small, flat, round red spots under the skin
- unusual bruising or bleeding
- continued oozing or bleeding from minor cuts
Carry an identification card or wear a bracelet stating that you take warfarin. Ask your pharmacist or doctor how to obtain this card or bracelet. List your name, medical problems, medications and dosages, and doctor's name and telephone number on the card.
Tell all your healthcare providers that you take warfarin.
Do not let anyone else take your medication. Ask your pharmacist any questions you have about refilling your prescription.
It is important for you to keep a written list of all of the prescription and nonprescription (over-the-counter) medicines you are taking, as well as any products such as vitamins, minerals, or other dietary supplements. You should bring this list with you each time you visit a doctor or if you are admitted to a hospital. It is also important information to carry with you in case of emergencies.
AHFS® Consumer Medication Information. © Copyright, The American Society of Health-System Pharmacists, Inc., 7272 Wisconsin Avenue, Bethesda, Maryland. All Rights Reserved. Duplication for commercial use must be authorized by ASHP.
Last Reviewed: September 1, 2010.