Font Size

Warfarin: Taking Your Medicine Safely

What is an Actionset?

Warfarin is a medicine that helps prevent blood clots. Because it prevents clots, it also helps prevent heart attacks, strokes, and other problems caused by blood clots.

It's important to know how to take warfarin safely.

Return to topic:

Warfarin is a pill that you take regularly to help prevent blood clots. Coumadin is the common brand name for warfarin.

Warfarin is often called a "blood thinner," although it doesn't really thin your blood. It works by increasing the time it takes for blood clots to form. Warfarin also keeps an existing clot from getting larger.

Warfarin is taken to prevent serious problems that are caused by blood clots. These problems can be life-threatening. They include stroke, heart attack, and pulmonary embolism. If you are at risk for one of these problems, your doctor may prescribe warfarin for you. For example, warfarin is taken by people who:

Some people also take warfarin while they recover from certain types of surgery, such as a hip replacement.

Test Your Knowledge

When I take warfarin, my blood takes longer to clot.


Taking warfarin safely is important, because it can cause bleeding problems. You will get regular blood tests to make sure you are getting the safest dose possible.

But because warfarin slows the amount of time it takes for your blood to clot, you need to be extra careful. Bleeding problems can happen when you:

  • Fall or are injured. An injury could cause bleeding that is hard to control. It's very important to take extra care to prevent injuries and falls.
  • Take other medicines. Taking certain other medicines along with warfarin can cause a bad reaction. For example, some medicines can change the way warfarin works so you bleed too easily. Or warfarin can change the way the other medicine works. Don't start or stop taking any other medicines, vitamins, or other supplements unless you talk to your doctor first.
  • Suddenly change how much vitamin K you eat.Vitamin K in the foods you eat helps your blood to clot and keeps your bones strong. If you are taking warfarin, it's important to keep the amount of vitamin K in your diet steady.

Test Your Knowledge

I need to be careful to avoid injury when I take warfarin.


Warfarin causes you to bleed more quickly when you're injured. So be sure to avoid doing things that increase your chances of bleeding. These are the four main steps you need to take:

  1. Get regular blood tests.
  2. Prevent falls and injuries.
  3. Be careful with other medicines.
  4. Eat a similar amount of vitamin K every day.

1. Get regular blood tests.

Regular blood tests will help your doctor make sure you are taking the right amount of warfarin.

Things like an infection or a small change in your diet can change the way warfarin works. So can other medicines that you are taking. That's why regular testing is so important. The tests tell your doctor whether your dose needs to be changed.

Don't change your dose or stop taking warfarin unless your doctor tells you to.

2. Prevent falls and injuries.

Make these changes in your life to prevent falls:

  • Wear slippers or shoes that have nonskid soles.
  • Use a cane or walker if you need one.
  • Put things within easy reach so that you don't need to reach over your head for them.
  • Keep a cordless phone and a flashlight with new batteries by your bed.

Make these changes in your home to prevent falls:

  • Remove raised doorway thresholds, throw rugs, and clutter.
  • Rearrange furniture and electrical cords to keep them out of walking paths.
  • Keep stairways, porches, and outside walkways well lit. Use night-lights in hallways and bathrooms.
  • Install sturdy handrails on stairways. Install grab handles and nonskid mats inside and outside your shower or tub and near the toilet.
  • Add extra light switches if needed or use remote switches, such as sound-activated switches, on lights by doors and near your bed. Then you will not have to get up quickly to turn on the light or walk across the room in the dark.
  • Repair loose carpet or raised areas in the floor that may cause you to trip.
  • Use shower chairs and bath benches.
  • Use nonskid floor wax. Wipe up spills right away, especially on ceramic tile floors.
  • If you live in an area that gets snow and ice in the winter, have a family member or friend sprinkle salt or sand on slippery steps and sidewalks.

Make these changes to prevent injuries:

  • Enjoy activities that have a lower risk of injury, like swimming and walking. Try to avoid activities or sports that put you at risk of injury. But if you take part in activities that put you at risk of falling or injury, be as safe as possible and wear protective equipment like helmets.
  • Be extra careful when you work with sharp tools or power tools, such as saws.
  • Use an electric razor, not a razor blade.
  • Use waxed dental floss and a toothbrush with soft bristles.
  • When you work outside, wear clothing that protects you, such as gloves, shoes, and long sleeves.

3. Be careful with other medicines.

Taking other medicines along with warfarin can cause a bad reaction. For example, some medicines can change the way warfarin works so you bleed too easily. Or warfarin can change the way the other medicine works.

Talk to your doctor before you start or stop taking any prescription medicines, over-the-counter medicines, vitamins, or herbal products. If other doctors prescribe something for you, be sure they know that you take warfarin. Here are some examples of medicines that you need to be careful of:

  • Over-the-counter medicines
  • Vitamins and herbal products
    • Cranberry products
    • Garlic pills
    • Green tea leaves. (Green tea leaves contain vitamin K before they are steeped in water, but a small serving of the hot tea itself does not.)
    • Ginkgo biloba
    • Multivitamins
  • Prescription medicines
    • Many medicines affect warfarin or are affected by warfarin.
    • Make sure your doctor knows everything you are taking.

Follow these safety tips for taking medicines:

  • Take your medicine at the same time each day. Most people take their warfarin in the evening.
  • Don't start or stop taking any medicines, vitamins, or natural remedies unless you first talk to your doctor.
  • If you take several medicines, use a daily medicine planner to keep track of them. It's a list of every medicine and vitamin you take, along with when and how often you take each one. You can make your own list or use this medicine planning sheetClick here to view a form.(What is a PDF document?).
  • Make sure that every doctor and dentist you see knows that you are taking warfarin.

What to do if you miss a dose of your warfarin

If you miss a dose of warfarin, the best thing to do is call your doctor. He or she can tell you exactly what to do so you don't take too much or too little. That way you'll stay as safe as possible.

But here are some general rules:

  • If you remember it in the same day, take the missed dose. Then go back to your regular schedule.
  • If it is the next day or almost time to take the next dose, do not take the missed dose. Do not double the dose to make up for the missed one. At your next regularly scheduled time, take your normal dose.
  • If you miss your dose for 2 or more days, call your doctor.

4. Eat a similar amount of vitamin K every day.

Most people who take warfarin can eat normally. But make sure that you don't suddenly eat a lot more or a lot less food that is high in vitamin K than you usually do.

Vitamin K helps your blood to clot so wounds don't bleed too much. Warfarin makes blood clots form more slowly. Suddenly changing the amount of vitamin K you eat each day could keep warfarin from working well.

How to get a steady amount of vitamin K

  • Don't suddenly change the amount of vitamin K in your diet. Try to keep the amount you eat about the same from day to day. For example, if you don't regularly eat leafy greens, such as spinach, don't suddenly add them to your diet or eat a lot at once.
  • Learn which foods contain vitamin K.
  • If you are used to eating foods that are high in vitamin K, you don't need to change your diet. What is important is to try to keep the amount about the same from day to day.
  • If you take a multivitamin that contains vitamin K, be sure you take it every day.
  • Check with your doctor before you take any supplements or herbal products. Some of these may contain vitamin K.
  • Check with your doctor before you make big changes in what you eat, such as starting a diet to lose weight.

Foods that are medium-high to high in vitamin K

  • Leafy green vegetables, such as kale, cabbage, spinach, turnip greens, collard greens, Swiss chard, mustard greens, seaweed, beet greens, lettuce, and endive
  • Canola and soybean oils
  • Brussels sprouts
  • Cauliflower
  • Broccoli
  • Asparagus
  • Parsley

More safety tips

Follow these general rules when you take warfarin:

  • Wear a medical alert IDClick here to see an illustration.. These are bracelets, pendants, or charms that let others know you take warfarin. Ask your pharmacist for information about ordering one. Medical alert jewelry is also easy to find on the Internet.
  • Don't smoke. Smoking affects how the body uses medicine, and it increases the blood's clotting effects.
  • Know what beverages to limit or avoid. Some beverages can change how warfarin works.
    • Limit alcohol to 2 drinks a day if you are a man, or 1 drink a day if you are a woman.
    • Avoid cranberry juice.
  • Tell your doctor if you are not able to eat for several days or if you have an upset stomach, diarrhea, or fever.
  • Before a surgery or procedure, tell your doctors that you take warfarin. Your doctor will tell you if you should stop taking it before your surgery. Make sure that you understand exactly what your doctor wants you to do. Your doctor will tell you when it is safe to start taking warfarin again.

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.

Know the signs of bleeding

Call 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.)

Be on the alert for signs of bleeding, and 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 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.

Test Your Knowledge

I should stop eating anything that contains vitamin K.


Now that you have read this information, you are ready to make sure you are taking your warfarin safely.

Talk with your doctor

If you have questions about this information, print it out and take it with you when you visit your doctor. You may want to mark areas or make notes where you have questions.


American Heart Association (AHA)
7272 Greenville Avenue
Dallas, TX 75231
Phone: 1-800-AHA-USA1 (1-800-242-8721)
Web Address:

Visit the American Heart Association (AHA) website for information on physical activity, diet, and various heart-related conditions. You can search for information on heart disease and stroke, share information with friends and family, and use tools to help you make heart-healthy goals and plans. Contact the AHA to find your nearest local or state AHA group. The AHA provides brochures and information about support groups and community programs, including Mended Hearts, a nationwide organization whose members visit people with heart problems and provide information and support.

Web Address:

CardioSmart is an online education and support program that can be your partner in heart health. This website engages, informs, and empowers people to take part in their own care and to work well with their health care teams. It has tools and resources to help you prevent, treat, and/or manage heart diseases.

You can set health and wellness goals and track your progress with online tools. You can track your weight, waist measurement, blood pressure, and activity. You can use calculators to help you find your body mass index (BMI) and check your risk for heart problems. You can search for a cardiologist. And you can find medicine information and prepare for your next appointment. Also, you can join online communities to connect with peers and take heart-healthy challenges.

CardioSmart was designed by cardiovascular professionals at the American College of Cardiology, a nonprofit medical society. Members include doctors, nurses, and surgeons.

Other Works Consulted

  • Agency for Healthcare Research and Quality (2010). Blood Thinner Pills: Your Guide to Using Them Safely (AHRQ Publication No. 09-0086-C). Rockville, MD: Agency for Healthcare Research and Quality. Available online:

ByHealthwise Staff
Primary Medical ReviewerE. Gregory Thompson, MD - Internal Medicine
Specialist Medical ReviewerJeffrey S. Ginsberg, MD - Hematology
Last RevisedApril 10, 2013

eMedicineHealth Medical Reference from Healthwise

This information does not replace the advice of a doctor. Healthwise disclaims any warranty or liability for your use of this information. Your use of this information means that you agree to the Terms of Use. How this information was developed to help you make better health decisions.

To learn more visit

© 1995-2014 Healthwise, Incorporated. Healthwise, Healthwise for every health decision, and the Healthwise logo are trademarks of Healthwise, Incorporated.

Medical Dictionary