Warfarin is a medicine that makes your blood less likely to form clots. This may be important if:
You have already had blood clots in your leg, arm, heart, or brain.
Your doctor is worried that a blood clot may form in your body. People who have a new heart valve, a large heart, a heart rhythm that is not normal, or other heart problems may need to take warfarin.
When you are taking warfarin, you may be more likely to bleed, even from activities you have always done.
Changing how you take your warfarin, taking other medicines, and eating certain foods all can change the way warfarin works in your body. If this happens, you may be more likely to form a clot or have bleeding problems.
It is important that you take warfarin exactly as your doctor told you to.
Take only the dose your doctor has prescribed. If you miss a dose, call you doctor or nurse for advice.
If your pills look different from your last prescription, call your doctor or pharmacist right away. The tablets are different colors, depending on the dose. The dose is also marked on the pill.
Your doctor or nurse will test your blood at regular visits. This is called an INR test or sometimes a PT test. The test helps make sure you're taking the right amount of warfarin to help your body.
Alcohol and some medicines can change how warfarin works in your body.
Do not drink alcohol while you are taking warfarin.
Talk with your doctor before taking any other over-the-counter medicines, vitamins, supplements, cold medicines, antibiotics, or other drugs.
Tell all of your health care providers that you are taking warfarin. This includes doctors, nurses, and your dentist. Sometimes, you may need to stop or take less warfarin before a medical or dental procedure. Always talk to the doctor who prescribed the warfarin before stopping or changing your dose.
Ask your doctor about wearing a medical alert bracelet or necklace that says you are taking warfarin so that health care providers who take care of you in an emergency will know.
Some foods can change the way warfarin works in your body. Make sure you check with your doctor before making any big changes in your diet.
You do not have to avoid these foods, but try to eat or drink only small amounts of them. In the least, do not change much of these foods and products you eat day-to-day or week-to-week:
Mayonnaise and some oils, such as canola, olive, and soybean oils
Broccoli, Brussels sprouts, and raw green cabbage
Endive, lettuce, spinach, parsley, watercress, garlic, and scallions (green onions)
Kale, collard greens, mustard greens, and turnip greens
Cranberry juice and green tea
Fish oil supplements, herbs used in herbal teas
Because being on warfarin can make you bleed more than usual:
You should avoid activities that could cause an injury or open wound, such as contact sports.
Use a soft toothbrush, waxed dental floss, and an electric razor. Be extra careful around sharp objects.
Prevent falls in your home by having good lighting and removing loose rugs and electric cords from pathways. Do not reach or climb for objects in the kitchen. Put things where you can get to them easily. Avoid walking on ice, wet floors, or other slippery or unfamiliar surfaces.
Make sure you look for unusual signs of bleeding or bruising on your body.
Look for bleeding from the gums, blood in your urine, bloody or dark stool, nosebleeds, or vomiting blood.
Women need to watch for extra bleeding during their period or between periods.
Dark red or black bruises may appear. If this happens, call your doctor right away.
When to Call the Doctor
Call your doctor if you have:
A serious fall, or if you hit your head
Pain, discomfort, swelling at an injection or injury site
A lot of bruising on your skin
A lot of bleeding (such as nosebleeds or bleeding gums)
Bloody or dark brown urine or stool
Headache, dizziness, or weakness
A fever or other illness, including vomiting, diarrhea, or infection
You become pregnant or are planning to become pregnant
David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine. Also reviewed by A.D.A.M. Health Solutions, Ebix, Inc., Editorial Team: David Zieve, MD, MHA, Bethanne Black, Stephanie Slon, and Nissi Wang