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Star Bulletin Alan Titchenal & Joannie Dobbs Health Options
Alan Titchenal
 & Joannie Dobbs
                  Monday, June 13, 2005


Mango, other foods affect blood thinners

blood-thinning drugs can interact with certain foods and drugs in ways that are potentially life-threatening. A comprehensive review of research studies evaluating these effects was recently published in the journal Archives of Internal Medicine. It raised some important concerns and a few surprises.

Question: What are blood thinner drugs?

Answer: The most common are technically known as anticoagulant drugs. They are used to prevent the formation of dangerous blood clots in people with coronary artery disease and other medical conditions related to blood flow.

Warfarin, the most commonly prescribed blood thinner, also is known by the brand name Coumadin. It works by decreasing the ability of blood to form clots.

Q: What are the risks?

A: Warfarin is truly a lifesaving drug for those who need it, but it is somewhat challenging to use because it requires good cooperation between physician and patient. Blood levels of the drug must be kept within a range that is both effective and safe. If the dose is too low, the drug will not have its intended effect. If the dose is too high, the blood will not clot when it should, potentially leading to dangerous internal bleeding. Consequently, both under- and over-dosing with warfarin can cause a stroke.

The right dose can vary greatly from one person to another, so dosage must be adjusted by frequent monitoring of the patient's blood-clotting ability. Changes in foods eaten or drugs taken can change the effects of warfarin and require an adjustment in dosage.

Q: Which drugs interact with warfarin?

A: A complete list is too long to present here, but one can be found in the May 23 issue of the Archives of Internal Medicine at

Some of the drugs that can increase the effects of warfarin include acetaminophen, some types of antibiotics, antidepressants, anti-fungal and anti-inflammatory drugs, and some drugs used to lower blood triglycerides. Clearly, before taking any new drug, someone taking warfarin should always check with his or her physician and pharmacist.

Q: Which foods interact with warfarin?

A: People taking warfarin must avoid foods high in vitamin K, such as dark green leafy vegetables, because the vitamin decreases the effectiveness of warfarin. A list of the vitamin K content in foods can be found at Other potential inhibitors of warfarin include soy milk, seaweeds, ginseng and large amounts of avocado.

Some surprising things that can increase the action of warfarin include mango, grapefruit juice and a variety of herbal supplements.

Alan Titchenal, Ph.D., C.N.S. and Joannie Dobbs, Ph.D., C.N.S.
are nutritionists in the Department of Human Nutrition, Food and Animal Sciences,
College of Tropical Agriculture and Human Resources, UH-Manoa.
Dr. Dobbs also works with the University Health Service

© 2005 Honolulu Star-Bulletin --

Human Nutrition, Food & Animal Sciences · University of Hawai`i at Mānoa
1955 East-West Road · Honolulu, HI 96822
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