What is warfarin?

Warfarin sodium is an anticoagulant medication. "Anti" means against and "coagulant" means causing blood clotting. Warfarin controls the way that blood clots (thickens into a lump) inside your blood vessels. The brand names of warfarin are Coumadin® and Jantoven®.

What do anticoagulants like warfarin do?

An anticoagulant helps your body control how fast your blood clots, which helps prevent unwanted clots from forming inside your arteries, veins, or heart during certain medical conditions and during long periods of physical inactivity.

If you have a blood clot, an anticoagulant may keep the clot from getting larger. It also may prevent a piece of the clot from breaking off and traveling to your lungs, brain or heart. An anticoagulant also helps prevent new clots from forming.

An anticoagulant does not dissolve the blood clot. With time, however, a clot may dissolve on its own.

How do I take warfarin?

You will take warfarin every day. The dose usually ranges from 1 mg to 10 mg. Your healthcare provider will prescribe a specific dosage strength, however, keep in mind that this dosage may change based on the results of each laboratory test.

Other instructions for taking warfarin include:

  • Take your dose of warfarin as instructed once a day.
  • Take the dose at the same time each day. We recommend 5:00 p.m.
  • Warfarin can be taken before or after eating.
  • If you forget to take your dose and remember within eight hours of the time you were supposed to take your dose, take the dose. If it is past eight hours, wait until the next day and take only the prescribed dose for that day. DO NOT TAKE A DOUBLE DOSE.
  • If you forget to take your warfarin two or more days in a row, call your healthcare provider. The dose may need to be changed. (Never change the dose yourself without calling your provider first.)
  • Consider using a pillbox to help you remember to take your medication or get a calendar and check off every day after you take your dose.
  • Refill your prescription one week before your supply runs out to avoid missing a dose.
  • Continue to take warfarin as long as your provider prescribes it. Never stop taking warfarin on your own without discussing this with your provider.

Tablet appearance

Warfarin is made by several drug manufacturers and is available as a tablet in many different shapes, sizes and colors. Each tablet color represents a different strength, measured in milligrams (mg). All manufacturers follow the same color code for the different strengths of their tablets, however, the size and shape of the tablets may differ from one manufacturer to the next.

Dosage StrengthTablet Color
1 mgpink
2 mglavender
2.5 mggreen
3 mgtan
4 mgblue
5 mgpeach
6 mgteal or blue-green
7.5 mgyellow
10 mgwhite

Each tablet has its strength stamped on one side and is scored (has an indent across the tablet) so it can easily be broken in half if your healthcare provider adjusts your dose. For example: if your provider prescribes a 5-mg tablet and then changes your dose to 2.5 mg (2½ mg), which is half the strength, you should break one of the 5-mg tablets in half and take the half-tablet. If you have any questions about your dose of warfarin, contact your provider.

What blood tests will I need while I am on warfarin?

You will need to have your blood tested to tell how well the medication is working. The blood test, called prothrombin time (PT or protime), is used to calculate your International Normalized Ratio (INR). Your INR helps your healthcare provider determine how well warfarin is working to prevent blood clots and if the dose needs to be adjusted.

Blood tests are done at a laboratory or anticoagulation clinic, in a medical office or at home. Blood tests are typically done from one or more times a week to once a month (if your results have been stable). Follow your provider’s instructions for how often you need to get blood tests and when to adjust your daily warfarin dose.

Other information about your blood tests:

  • Illness, health status, diet or medication changes can affect your INR. Tell your healthcare provider about changes in your health, medications (prescription and over-the-counter) or lifestyle so appropriate dosage adjustments can be made.
  • If you are planning a trip, talk with your provider about using another laboratory for your blood tests while traveling.

Where should I store warfarin?

Store warfarin at room temperature, away from extreme cold, heat, light and moisture. Never store medications in bathroom cabinets because of the moisture found in bathrooms.

Always keep medications out of the reach of children and pets.

What precautions should I take while taking warfarin?

It is important that you follow these precautions when taking warfarin.


It is important to avoid getting pregnant while on warfarin. Use reliable birth control methods to prevent pregnancy if you are a female and have not yet reached menopause.

If you are taking warfarin and planning to become pregnant, talk with your doctor about the possible risks and ways to reduce those risks. Tell your doctor right away if you become pregnant or think you might be pregnant.

Surgery and dental work

Before receiving any treatment, tell all of your doctors and dentists you are taking warfarin. You may need to have a blood test and stop taking warfarin for a few days before having surgery or a dental procedure.

Be sure to contact your healthcare provider who monitors your warfarin at least two weeks before any dental or surgical procedure if possible. Do not stop taking warfarin without talking to your healthcare provider first.


Check with your provider before starting any exercise or sports program. Talk with your provider if you are planning any major diet changes such as a weight-reducing diet, or if you plan to add any nutritional supplements.


Foods and vitamin K. Vitamin K is needed for normal blood clotting. However, large changes in the amount of vitamin K in your diet can change the way warfarin works. If you eat foods high in vitamin K, it’s important to keep your weekly intake of vitamin K-containing foods consistent.

Tell your provider if you are thinking about changing your current eating habits. Tell your provider if you are planning to:

  • Eat more or fewer vegetables.
  • Change to a vegetarian style of eating.
  • Follow a special meal plan to lose or gain weight.

Changing your eating habits may mean that you will be getting more or less Vitamin K in the foods you eat. If you change your eating habits, your provider may want to check your blood more frequently to see how warfarin is working.

The vegetables listed below are known to have high amounts of vitamin K per serving. Although it is important to be aware of foods high in vitamin K, it is also important that you eat a well-balanced diet.

Green Leafy Vegetables
Collard, mustard and turnip greens
Endive, lettuce (Boston, bib, head, red leaf and romaine)

Cruciferous Vegetables
Brussels sprouts

If you want more servings of vegetables in your daily meal plan, choose vegetables that are not high in Vitamin K, such as corn, squash, potatoes, onions, carrots, cucumbers, celery, peppers, pumpkin, and tomatoes.

Herbal teas. Do not start consuming the following herbal teas and supplements because they may affect the INR, causing it to be too high or too low. If you drink tea, black tea (such as orange pekoe tea) is acceptable because it is not high in Vitamin K.

Herbal Teas
Melitot (sweet clover)
Sweet woodruff
Green tea
Mint tea
Tonka beans

Herbal supplements. The following herbal supplements may affect the INR, causing it to be too high or too low. Certain foods like celery, clove, garlic, ginger, and parsley are usually safe if they are used in small amounts in cooking or as a seasoning (these are marked by an asterisk [*].) They should not be used in the form of a supplement.

Herbal Supplements
Alfalfa/alfalfa sproutsFenugreekMeadow
Angelica (dong quai)FeverfewPapain
BromelainGinger*Passion flower
Celery*Gingko bilobaQuassia
Coenzyme Q-10 (ubiquinone, CoQ10)Green teaRed clover
DanshenHorse chestnut (buckeye, aesulus)Reishi mushroom
Devil's clawKelpwareRue
EchinaceaLicoriceSt. John's wort

Other dietary tips:

  • Avoid grapefruit, pomegranate, and cranberry products.
  • Eat all other foods as you normally would.
  • The following herbal supplements may keep your blood from clotting and should not be used when you are taking anticoagulant medications before surgery:
    • Garlic.
    • Ginger.
    • Gingko biloba.
    • Ginseng.
    • Feverfew.
    • Fish oil.
    • Turmeric.
    • St. Johns Wort.
    • Chondroitin sulfate.
  • Do not take any vitamin supplements that provide more than 100 percent of the Recommended Daily Allowance (RDA). Tell your doctor if you are currently taking more than the RDA of any vitamins (especially vitamins A, C or E).
  • Nutritional supplements including Boost® and Ensure® can also affect warfarin levels. Ask your healthcare provider about the suitability of taking these products.
  • Alcohol increases the risk of major bleeding. Ask your healthcare provider if it's safe for you to drink alcoholic beverages while you are taking warfarin.


Some medications may increase the anticoagulant effect of warfarin; others may decrease the effect. You might need to get blood tests more often when you stop, start or increase the dose of medications that are likely to affect the way warfarin works. The dosage of warfarin may need to be adjusted too. Talk to your healthcare provider who manages your warfarin if you have any changes in your other prescription medications.

Medicines that May DECREASE the Effectiveness of Warfarin
Carbamazepine (Tegretol®)
Phenobarbital (Luminal®)
Phenytoin (Dilantin®)
Rifampin (Rifadin®)
Vitamin K Multiple brands
Cholestyramine (Questran® Questran Light®)
Sucralfate (Carafate®)
This is a sample list and does not include all drugs that may interfere with warfarin.

Medicines that May INCREASE the Effectiveness of Warfarin
Amiodarone (Cordarone®, Pacerone®)
Co-trimoxazole (Bactrim®, Septra®)
Ciprofloxacin (Cipro®)
Clarithromycin (Biaxin®)
Erythromycin Multiple brands
Fluconazole (Diflucan®)
Itraconazole (Sporanox®)
Ketoconazole (Nizoral®)
Lovastatin (Mevacor®)
Metronidazole (Flagyl®)
This is a sample list and does not include all drugs that may interfere with warfarin.

This is NOT a complete listing of medications that can affect the way warfarin works. In fact, many non-prescription medications can also affect how warfarin works. Some examples include acetaminophen (Tylenol®), aspirin, nonsteroidal anti-inflammatory drugs (NSAIDs) (such as ibuprofen, naproxen or ketoprofen and cold and cough medicines that contain NSAIDS), antacids, laxatives, or other medications for pain or discomfort.

Always check with the healthcare provider who monitors your warfarin BEFORE taking any over-the-counter medication, herbal product, natural remedy, nutritional supplement or prescription medication from another healthcare provider or dentist. Your healthcare provider may need to adjust your warfarin dose or may recommend another medication or product less likely to interfere with warfarin. Do not stop or start any medications without first talking to your healthcare provider.

Daily activities

  • Be careful when using razors. Use an electric razor or hair-removing creams to lessen the chance of cuts.
  • Use a soft toothbrush. Brush and floss gently to prevent bleeding from the gums.

Illness and emergencies

  • Keep your healthcare provider’s phone number with you in the event of an emergency.
  • Call your healthcare provider if you have any symptoms of illness, such as vomiting, diarrhea, infection, or fever. Illness can change the way warfarin works.
  • Always carry or wear identification that states you are taking warfarin. In an emergency, you may not be able to speak for yourself.
  • Avoid situations at home or work that might lead to an injury. Even minor injuries must be watched for bleeding because warfarin affects clotting. Falls that cause bruising (bleeding under the skin) and cuts from sharp objects are more serious when you are taking warfarin. Call your doctor if you have any injuries from falls or blows to your body or head.


  • Check with your doctor before you travel. You may need to have a blood test and an adjustment to your warfarin dose before you leave.
  • While traveling, carry your medications with you at all times. Do not put medications in checked baggage and do not leave them in the car.
  • If seated for long periods of time during travel, get up and walk if possible or perform foot and leg raises.

What should I do if I cut myself while on warfarin?

If you cut yourself and the cut is small, apply constant pressure over the cut until the bleeding stops. This may take up to 10 minutes. If the bleeding doesn't stop, continue to apply pressure and go to the nearest emergency room.

If you cut yourself and the cut is large, apply constant pressure and get help immediately either by calling 911 or your local emergency number or by having someone drive you to the nearest emergency room.

What are the side effects of warfarin?

Bleeding is the most common side effect of warfarin and can appear as any of several different symptoms. Call your doctor if you notice any of the following signs of bleeding:

  • Feeling more cold, weak, or tired than usual or looking pale (symptoms of anemia).
  • Bleeding from cuts that won't stop after applying pressure for 10 minutes.
  • Bleeding from the nose, gums, or ears that will not stop after 10 minutes.
  • A fever or illness that gets worse.
  • Menstrual bleeding (period) that is heavier or lasts longer than normal.
  • Reddish or rusty-colored urine.
  • Bowel movements that look bright red, black or tarry.
  • Bruises that appear without reason or become swollen or painful; purplish spots on your skin.
  • Coughing up blood.
  • Vomiting blood (which may look like coffee grounds).
  • Unusual bleeding from hemorrhoids.
  • Unusual pain or swelling, especially in the joints.
  • Unusual headache.
  • Stomach or abdominal pain.
  • Sudden changes in speech or vision.
  • Numbness/tingling on one side of the face or in the arm.
  • Dizziness.
  • Difficulty breathing.

If you have any of these symptoms, your provider may want to do a blood test, change your dose, stop the medication, or give you medicine to stop the bleeding.

Summary of important points to remember

  • Take your warfarin as instructed and at the same time each day.
  • Have your blood tested as instructed to check how your blood is clotting.
  • Discuss all medications you are taking -- even over-the-counter medicines -- with your doctor and pharmacist since many drugs can interact with warfarin.
  • Do NOT stop or start taking any medications, herbal products, natural remedies, or nutritional supplements without first talking to the provider who monitors your warfarin medication.
  • Tell anyone providing medical or dental care that you are taking warfarin.
  • Eat about the same amount of vitamin K-containing foods each week, as these foods can affect the way warfarin works.
  • If you forget to take a pill, DO NOT take a double dose. Take the missed dose as soon as possible on the same day. DO NOT take a double dose of warfarin the next day to make up for the missed dose.
  • Watch for signs of abnormal or excessive bleeding and bruising. Call your healthcare provider right away if you suspect something is wrong.
  • DO NOT change warfarin products without first checking with your doctor. Different brands of warfarin products may NOT be identical, and you may need to have your dose checked and adjusted more frequently if you change brands.
  • DO NOT STOP your warfarin even for a minor procedure like dental work without first checking with the doctor who monitors your therapy.
  • Alcohol can increase your risk of bleeding. Ask your healthcare professional if it's safe for you to drink alcoholic beverages while you are taking warfarin.

Last reviewed by a Cleveland Clinic medical professional on 12/05/2019.


  • Coumadin package insert. Bristol-Myers Squibb. Coumadin. (https://packageinserts.bms.com/pi/pi_coumadin.pdf) Accessed 1/3/2020.
  • Jantoven warfarin sodium tablets. Upsher-Smith. Jantoven. (https://www.upsher-smith.com/products/jantoven/) Accessed 1/3/2020.
  • Agency for Healthcare Research and Quality. Blood Thinner Pills: Your Guide to Using Them Safely. (http://www.ahrq.gov/sites/default/files/wysiwyg/patients-consumers/diagnosis-treatment/treatments/btpills/btpills.pdf) Accessed 1/3/2020.
  • American Heart Association. A Patient's Guide to Taking Warfarin. (https://www.heart.org/en/health-topics/arrhythmia/prevention--treatment-of-arrhythmia/a-patients-guide-to-taking-warfarin) Accessed 1/3/2020.
  • American Heart Association. Anticoagulation. (http://www.heart.org/HEARTORG/Conditions/CongenitalHeartDefects/TheImpactofCongenitalHeartDefects/Anticoagulation_UCM_307110_Article.jsp) Accessed 1/3/2020.

Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy