Warfarin side effects: Watch for interactions

Although commonly used to treat blood clots, warfarin (Coumadin) can have dangerous side effects or interactions that can place you at risk of bleeding. Here are precautions to take to avoid warfarin side effects. By Mayo Clinic Staff

If you've been prescribed warfarin (Coumadin, Jantoven) to prevent blood clots, you probably already know that this powerful drug can save your life if you're at risk of or have had blood clots. But you may not realize how serious warfarin side effects can be. Warfarin, especially if taken incorrectly, increases your risk of dangerous bleeding. Warfarin side effects can also include interactions with some foods, prescription medicines and over-the-counter supplements.

If your doctor prescribes warfarin for you, make sure you understand all the potential warfarin side effects and interactions it could have.

When is warfarin prescribed?

You might be given warfarin if you have:

  • A blood clot in or near your heart that could trigger stroke, heart attack or organ damage
  • A blood clot in your lungs (pulmonary embolism)
  • A blood clot elsewhere in your body (venous thrombosis)
  • A high risk of blood clots forming in the heart, such as in some heart rhythm abnormalities (arrhythmias)
  • A mechanical artificial heart valve that is prone to forming blood clots

What warfarin side effects should you watch for?

When you take warfarin, your blood won't clot as easily. If you accidentally cut yourself while taking warfarin, you may bleed heavily. You're more likely to have bleeding problems if you're older than 75 or take other blood-thinning medications that can further increase your bleeding risk.

Warfarin side effects that require immediate medical attention

  • Severe bleeding
  • Black stool or bleeding from the rectum
  • Skin conditions such as hives, a rash or itching
  • Swelling of the face, throat, mouth, legs, feet or hands
  • Bruising that comes about without an injury you remember
  • Chest pain or pressure
  • Nausea or vomiting
  • Fever or flu-like symptoms
  • Joint or muscle aches
  • Diarrhea
  • Difficulty moving
  • Numbness or tingling in any part of your body
  • Painful erection lasting four hours or longer

Although rare, warfarin can also cause skin tissue death (necrosis) and gangrene requiring amputation. This complication most often happens three to eight days after you start taking warfarin. If you notice any sores, changes in skin color or temperature, or severe pain on your skin, notify your doctor immediately.

Less serious warfarin side effects to tell your doctor about

  • Gas
  • Feeling cold
  • Fatigue
  • Pale skin
  • Changes in the way foods taste
  • Hair loss

What precautions can you take against warfarin side effects?

There are some key steps you can take to reduce your chance of developing warfarin side effects.

  • Tell your doctor about any other medications or supplements you take. Many medications and supplements can have a dangerous interaction with warfarin.
  • Tell your health care provider you take warfarin before you have any medical or dental procedures. Tell providers that you take warfarin even before minor procedures, such as vaccinations and routine dental cleanings. If you're going to have surgery, discuss what dosing changes might be necessary at least 10 days before the procedure. Your doctor may decrease your dose of warfarin or discontinue warfarin altogether before the procedure. Talk to the doctor who prescribed warfarin to find out if it's safe to discontinue for a few days. If you are at high risk of blood clots, you may need a shorter acting blood thinner, heparin, to keep a lower risk of blood clots while you're not taking warfarin.
  • Avoid situations that increase your risk of injury. Avoid contact sports or activities that could result in head injury. Make sure you tell your doctor if you are unsteady while walking or have a history of falling.
  • Consider wearing a bracelet or carrying a card that identifies that you take warfarin. This can be useful if emergency medical personnel need to know what medications you take.
  • Consider a warfarin sensitivity test. About a third of the people who take warfarin are at a higher risk of bleeding because their genes make them more sensitive to warfarin. If you're worried that you might be more sensitive to warfarin because a family member experienced side effects, talk to your doctor about taking a genetic warfarin sensitivity test. The test can tell if you have the genes that can increase your risk of bleeding, although researchers are still looking into whether genetic tests are more effective than carefully monitoring your body's response to warfarin.
  • If you receive new prescriptions from someone other than your usual medical provider, make sure to remind him or her that you're taking warfarin. Ask if you'll need additional blood tests from your regular care provider to make sure your blood clotting hasn't been affected by the new medications you're taking.
Feb. 16, 2012 See more In-depth