Skip to Content

Warfarin

Brand Name(s): Coumadin®, Jantoven®; also available generically

IMPORTANT WARNING:

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 month 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.

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.

Keep all appointments with your doctor and the laboratory. Your doctor will order a blood test (PT [prothrombin test] reported as INR [international normalized ratio] value) regularly to check your body's response to warfarin.

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 (https://www.fda.gov/downloads/Drugs/DrugSafety/ucm088578.pdf) or the manufacturer's website to obtain the Medication Guide.

Talk to your doctor about the risk(s) of taking warfarin.

WHY is this medicine prescribed?

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.

HOW should this medicine be used?

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.

Are there OTHER USES for this medicine?

This medication may be prescribed for other uses; ask your doctor or pharmacist for more information.

What SPECIAL PRECAUTIONS should I follow?

Before taking warfarin,

  • tell your doctor and pharmacist if you are allergic to warfarin, any other medications, or any of the ingredients in warfarin tablets. Ask your pharmacist or check the Medication Guide for a list of the ingredients.
  • 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 while taking warfarin. Your doctor may change the doses of your medications or monitor you carefully for side effects.
  • the following nonprescription or herbal products may interact with warfarin: coenzyme Q10 (Ubidecarenone), Echinacea, garlic, Ginkgo biloba, ginseng, goldenseal, and St. John's wort; omeprazole (Prilosec); famotidine (Pepcid AC); aspirin and nonsteroidal anti-inflammatory drugs (NSAIDS) such as ibuprofen (Advil, Motrin, others) and naproxen (Aleve). Be sure to let your doctor and pharmacist know that you are taking these medications before you start taking warfarin. Do not start any of these medications while taking warfarin without discussing with your healthcare provider.
  • tell your doctor if you have or have ever had 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. Pregnant women should not take warfarin unless they have a mechanical heart valve. 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.
  • ask your doctor about the safe use of alcoholic beverages while you are taking warfarin.
  • tell your doctor if you use tobacco products. Cigarette smoking may decrease the effectiveness of this medication.

What SPECIAL DIETARY instructions should I follow?

Eat a normal, healthy diet. Some foods and beverages, particularly those that contain vitamin K, can affect how warfarin works for you. Ask your doctor or pharmacist for a list of foods that contain vitamin K. Eat consistent amounts of vitamin K-containing food on a week-to-week basis. Do not eat large amounts of leafy, green vegetables or certain vegetable oils that contain large amounts of vitamin K. Be sure to talk to your doctor before you make any changes in your diet. Talk to your doctor about eating grapefruit and drinking grapefruit juice while taking this medication.

What should I do IF I FORGET to take a dose?

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. Call your doctor if you miss a dose of warfarin.

What SIDE EFFECTS can this medicine cause?

Warfarin may cause side effects. Tell your doctor if any of these symptoms are severe or do not go away:

  • gas
  • abdominal pain
  • bloating
  • change in the way things taste
  • 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:

  • hives
  • rash
  • itching
  • difficulty breathing or swallowing
  • swelling of the face, throat, tongue, lips, or eyes
  • hoarseness
  • chest pain or pressure
  • swelling of the hands, feet, ankles, or lower legs
  • fever
  • infection
  • nausea
  • vomiting
  • diarrhea
  • extreme tiredness
  • lack of energy
  • loss of appetite
  • pain in the upper right part of the stomach
  • yellowing of the skin or eyes
  • flu-like symptoms

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.

What should I know about STORAGE and DISPOSAL of 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.

Unneeded medications should be disposed of in special ways to ensure that pets, children, and other people cannot consume them. However, you should not flush this medication down the toilet. Instead, the best way to dispose of your medication is through a medicine take-back program. Talk to your pharmacist or contact your local garbage/recycling department to learn about take-back programs in your community. See the FDA's Safe Disposal of Medicines website (https://goo.gl/c4Rm4p) for more information if you do not have access to a take-back program.

It is important to keep all medication out of sight and reach of children as many containers (such as weekly pill minders and those for eye drops, creams, patches, and inhalers) are not child-resistant and young children can open them easily. To protect young children from poisoning, always lock safety caps and immediately place the medication in a safe location – one that is up and away and out of their sight and reach. https://www.upandaway.org

What should I do in case of OVERDOSE?

In case of overdose, call the poison control helpline at 1-800-222-1222. Information is also available online at https://www.poisonhelp.org/help. If the victim has collapsed, had a seizure, has trouble breathing, or can't be awakened, immediately call emergency services at 911.

Symptoms of overdose may include the following:

  • 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

What OTHER INFORMATION should I know?

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.

This report on medications is for your information only, and is not considered individual patient advice. Because of the changing nature of drug information, please consult your physician or pharmacist about specific clinical use.

The American Society of Health-System Pharmacists, Inc. represents that the information provided hereunder was formulated with a reasonable standard of care, and in conformity with professional standards in the field. The American Society of Health-System Pharmacists, Inc. makes no representations or warranties, express or implied, including, but not limited to, any implied warranty of merchantability and/or fitness for a particular purpose, with respect to such information and specifically disclaims all such warranties. Users are advised that decisions regarding drug therapy are complex medical decisions requiring the independent, informed decision of an appropriate health care professional, and the information is provided for informational purposes only. The entire monograph for a drug should be reviewed for a thorough understanding of the drug's actions, uses and side effects. The American Society of Health-System Pharmacists, Inc. does not endorse or recommend the use of any drug. The information is not a substitute for medical care.

AHFS® Patient Medication Information™. © Copyright, 2024. The American Society of Health-System Pharmacists®, 4500 East-West Highway, Suite 900, Bethesda, Maryland. All Rights Reserved. Duplication for commercial use must be authorized by ASHP.

Selected Revisions: June 15, 2017.


AHFS® Patient Medication Information™. © Copyright, 2024