Coumadin is known as a blood thinner or anticoagulant. That means it is prescribed to prevent the formation or recurrence of blood clots. People who experience a pulmonary embolism or thrombophlebitis in their legs often receive warfarin to reduce the risk of more serious complications. When clots are feared, this medicine may lower the likelihood of a heart attack or stroke.

Coumadin works by blocking key factors necessary for normal blood coagulation. Vitamin K plays an important role in this process. Getting the right dose can be a very tricky process. Too little warfarin may not allow for adequate clot protection, but too much could lead to life-threatening hemorrhage. Like Goldilocks and the porridge it may take some experimentation to get things just right. That requires frequent blood tests for prothrombin times, especially in the early phase of treatment.

Side Effects and Interactions:

Side effects of Coumadin therapy are uncommon if the dose is appropriate and blood tests are carefully monitored. Some people have occasionally reported hair loss, skin rash, itching, nausea, fever, digestive upset, diarrhea, hepatitis, purple toes, red-orange urine, prolonged, painful erections, and mouth ulcers. Report any such symptoms to your physician promptly.

A large number of over-the-counter and prescription medications may interact with Coumadin in a dangerous way. Some drugs, including barbiturates and the anticonvulsant Tegretol (carbamazepine), can reduce the effectiveness of Coumadin and increase the risk of blood clots. Others, such as the antibiotics metronidazole (Flagyl) or co-trimoxazole (Bactrim, Septra, etc.), can increase the blood thinning potential of Coumadin and thereby raise the risk of dangerous bleeding. The drugs Nolvadex (tamoxifen) and Danocrine (danazol) can also increase susceptibility to hemorrhage when a woman is taking Coumadin.

Because aspirin also acts as an anticoagulant, though it works differently from Coumadin, it should be avoided unless your doctor specifically prescribes it and monitors bleeding time. The heart drug Cordarone (amiodarone), the ulcer drug Tagamet (cimetidine), anabolic steroids such as Anadrol-50 (oxymetholone) and antibiotics such as Biaxin (clarithromycin), erythromycin or tetracycline can also make hazardous bleeding more likely for people on Coumadin. Some individuals may also be vulnerable to increased bleeding when they take the antidepressants Paxil (paroxetine), Prozac (fluoxetine) or Zoloft (sertraline). Also beware of quinine derivatives prescribed for the heart.

Patients should be wary of taking thyroid drugs, cholesterol medications and tuberculosis medicines in combination with warfarin. Vitamins E and K could also be problematic. Consult with the prescribing physician before making any changes in the regimen. Coenzyme Q10 may counteract the benefits of warfarin. Anticoagulants such as Coumadin may pose a hazard when taken with the herb ginkgo biloba. An elderly woman on Coumadin had a hemorrhagic stroke after two months of ginkgo. If the extract of the herb hawthorn is taken together with Coumadin, careful monitoring of bleeding time (through PT and INR) is essential. The anticlotting action of the herb horse chestnut (aesculin) may interact with Coumadin to increase the risk of bleeding. This combination should be avoided.

It is possible that juniper berries may interact with Coumadin to increase the risk of bleeding. This possibility remains hypothetical. Licorice binds to serum albumin and may interact with Coumadin. The coumarins in licorice may also potentiate the action of Coumadin, possibly leading to unexpected bleeding. Despite research suggesting that ginseng might reduce platelet aggregation, the only reported interaction with Coumadin resulted in a decreased INR (international normalized ratio, a measure of blood clotting propensity). This suggests that ginseng might possibly counteract the benefit of warfarin. A red clover extract containing coumarin derivatives might in theory interact with the anticoagulant Coumadin. Close monitoring of prothrombin time or INR is advisable.

Psyllium can affect the absorption of Coumadin. To avoid this, psyllium should be taken at least an hour after Coumadin. In theory, garlic could increase the risk of bleeding in people taking anticoagulants such as Coumadin. The herb pau d’arco causes vitamin K-reversible bleeding, strongly suggesting that it would interact with Coumadin to increase the danger of hemorrhage. The anticoagulant activity of astragalus may interact with that of warfarin, increasing the risk of bleeding. This herb capsicum (cayenne) may have the potential to prolong clotting time, so people taking Coumadin should exercise caution before eating quantities of chili peppers. Cayenne also inhibits liver enzymes (CYP1A2) and thus could potentially slow the metabolism of warfarin.

In theory the coumarins in the herb chamomile might potentiate Coumadin’s effect. Careful monitoring of bleeding time (through PT and INR) are recommended if chamomile is to be used together with Coumadin. One woman was hospitalized with internal bleeding after consuming chamomile tea regularly while taking Coumadin. (CMAJ, Apr. 25, 2006) Also in theory, the herb feverfew could increase the risk of bleeding in people taking Coumadin. Because ginger inhibits prostaglandin synthesis and reduces platelet aggregation, caution should be exercised in combining it with warfarin. The combination could result in unexpected bleeding. It is not known whether the coumarins in the herb dong quai might interact with Coumadin. To be safe, any woman taking both dong quai and Coumadin should discuss this situation with her doctor and should have bleeding time (PT and INR) checked frequently, especially when starting or stopping the herb. Goldenseal reportedly limits the effectiveness of the Coumadin. As a general rule, do not take any other medication or herbs without first checking with your physician and pharmacist.

Taking the Medicine:

Although the absorption of Coumadin may be slightly slowed by food, the medicine can be taken at meal time, especially if it upsets your stomach. There are, however, certain foods that may reduce the effectiveness of this drug. Because Vitamin K can counteract the action of warfarin, it is important to get approximately the same amount of this vitamin every day. Be careful not to overdo suddenly on foods that are rich in this nutrient. These include broccoli, cabbage, spinach, collard greens, kale, brussels sprouts and lettuce. This doesn’t mean that you must avoid such healthy vegetables, but don’t suddenly increase your intake without careful monitoring of prothrombin time. (For a more complete list, see our Guide to Coumadin Interactions.) The same warning would hold if you suddenly dropped one of these from your diet completely.

Special Precautions:

Anyone taking Coumadin must monitor his body carefully. Be alert for any early warning signs of bleeding. Symptoms to watch for include bruising or red spots under the skin, red or dark urine, red, black or tarry stools, nosebleeds, or bleeding around the gums after gentle tooth brushing. Internal hemorrhaging may manifest itself in a variety of ways, including pain in joints, chest, stomach or head. Shortness of breath, difficulty breathing or unexplained swelling could indicate bleeding. Alert your physician immediately if you notice any unusual symptoms or signs of spontaneous bleeding.

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  1. la femme 19894

    He was in hospital after Gillian startled him while he was using an angle-grinder and then nagged him mercilessly in the ambulance all the way to A&E. Poltergeists and the living dead would come as light relief.

  2. Mon

    Am on Warfarin my Cholesterol is VERY high 9.5 (in Australia) LDL is very high so is Triglycerides. My Cardiologist wants me to take Crestor (Statin) but some literature says it can it cause internal bleeding?
    Please somebody advise me

  3. Martha
    United States

    I have taken warfarin for about 6 years give or take. I used to do fine on 7.5 mgs every day now I am on 5mgs a day except the last 3 weeks when it was cut back to. 2.5 one day a week. My INR doesn’t do well. I have been at 3 then dropped down to 1.5 then back up to 2.9. I keep getting lumps on my body the size of quarters that sting real bad. Then it turns to a brush when the stinging goes away.

  4. Sue

    I take Coumadin and am out of range with 2.9. My doctor is not cutting the dose and I am nervous about taking more of the drug when I am already on the high side. I need some advice.

    • The People's Pharmacy

      You should point out your INR to the doctor and ask for his/her advice. It may be that this lab result got ignored or forgotten, but you can and should bring it to attention.

  5. Steve

    I had two heart attacks in November 2013 and have been on Warfarin since I left the hospital. I have been outside the US since July 2015 and bought a home tester, which works. I learned that in China they don’t prescribe warfarin because, the doctor told me, “if they (the patients) bleed to death, they blame us, but if they die, well, that’s there fault. Replacing the test strips was very expensive in China, but not so much in Thailand. Sometimes when I travel, my INR becomes erractic, but I am still traveling.

  6. bio

    I too have these bruise stains, one on my belly after injection replacement for warfarin. It lasted at least a year.
    The second one on my arm was quite a deep bruise and very large, and the standard has been there since april 2014 with no sign of shifting.
    The primary care doctors and consultants said it may take some time. They do not hurt but feel a little lumpy. Hope this helps

  7. Stephanie M

    I was on the Atkins diet and it dropped my INR from a healthy and regular 2-3 to 1.1. Not a good diet for warfarin takers. I finally got it up to 1.9 which was much better.
    My last test was 4.44 way above the 2-3 level. I think the South Beach diet is better. I did lose the weight but it scared me with the low reading.
    We are still working on getting it back to the 2-3 level. I hardly eat any greens and stick to my Cauliflower and sweet potatoes. My Doctor said the best diet was just to change your eating habits and do more exercise. I had read that the Warfarin attaches to the protein and reduces its potency. Let me know about your diet and hope it is something I can do too.

  8. anonymous

    I was prescribed warfarin because of a pulmonary embolism in November. I was in need of oxygen while on warfarin. One day on a doctors visit my o2 number was 66. Has this ever happened to anyone else? Now that I’m off of warfarin I have no need for oxygen in the daytime.

  9. yasmeem

    I am on warfarin and every month I check my blood. Before one month I had bleeding in my nose after that I stopped warfarin after one month I checked my blood and it was down is it ok to stop taking it? because I’m scared that again bleeding happens please answer me
    People’s Pharmacy response: No one should stop warfarin except with the doctor’s knowledge and supervision. It was prescribed for a reason and you need to make sure you no longer need it.

  10. Nancy

    I have been taking 5mg of warfarin daily for the past 3 years due to Afib. I also do monthly INR tests. My doctor just retired and the clinic where he practiced is no longer taking my insurance. I live on a small island and can not get any doctor to see me as a new patient until Nov 3 so therefore I can’t get my prescription filled or my blood tested. Any suggestion as to what I can use for an OTC warfarin substitute?

  11. gpt

    Have just started Coumadin, not quite a month. I notice there is a new burning of tongue, constipation and veins very prominent now. If this is normal I will power through, but would like to know if it is medication related. I take levothyroxine, metoprolol, crestor, fosamax once a week mag ox 400, fish oil 1000, vit d3 1000 any special order to take medications.

  12. Victoria B

    Simvastatin should not be used in super old ppl
    It makes muscles weak and tired.

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