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Frequently Asked Questions


Which herbs might cause problems with blood clotting?

Many common herbs and other dietary supplements can increase bleeding risk by increasing the time it takes blood to clot. This is especially important if you are taking the anti-coagulant drugs (like warfarin /Coumadin or heparin), NSAIDS (like Advil, Motrin, Ibuprofen), aspirin, COX-2 inhibitors (like Vioxx, Celebrex), or having surgery (Please Note - this list is not all-inclusive).

It is critical that you tell your health care providers (physician, pharmacist, dietitian, nurse, anaesthiologist, dentist, among others) about all of your medications and all types of your dietary supplements. They should check for potential interactions in order to lower the risk of possibly fatal complications. You may need to be taught to watch for signs and symptoms of increased bleeding (bruising, petechia, purpura, frank bleeding) and have some blood tests monitored (international normalized ratio - INR, prothrombin time - PT).

The American Society of Anesthesiologists recommends the discontinuation of all herbs at least 2 weeks prior to any surgery. The ASA has a helpful brochure to download from their website discussing this concern, which lists various herbs that may potentially complicate surgery an/or anesthesia.

Some of the more common herbs and dietary supplements that have data (some human case studies, some in vitro laboratory studies) to show anti-coagulant and anti-platelet potential are the following (this list is not all inclusive):

Angelica root
Bilberry Leaf
Black Cohosh
Borage seed oil
Fish oil (omega-3 fatty acids)
Ginkgo biloba
Green Tea
Horse chestnut
Licorice root
Panax Ginseng
Red clover
Sweet clover
Vitamin E
Willow bark

Some additional sources to read for more detailed information include the following Internet articles:

Internet articles -

(1) Herbal Medicines & Blood-Thinning Drugs: Risky Combination

(2) A Review of Herb-Drug Interactions: Documented and Theoretical - has information and lists of many other drug-herb interactions complete with references.

A highly recommended book to purchase for your home library is Herb-Drug Interactions by Sharon Herr, RD. Purchasing information is found at http://www.herbdrug.org
There are many herb-drug interactions to be avoided. This book will easily help you identify them.

Again, I cannot over-emphasize the importance of telling your health care providers about all of the dietary supplements (herbs, vitamins, minerals, and other over the counter products) that you are taking. Don't wait for them to ask you. Let the right hand know what the left hand is doing. It could save your life!

updated 8/03, 1/04


Back to Main QandA Page

Herbs and other Dietary Supplements

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These questions and answers are intended to be of a general informative nature. Please consult with the Registered Dietitian in your cancer center or your health care provider for nutritional advice that can be individualized to your specific medical condition.

Contact Information:
Phone/Fax: 734/996-9260

P.O. Box 130221, Ann Arbor, MI  48113

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