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Disease Prevention

Research Indicates St. John's Wort Hinders Critical Medications

Many consumers are taking advantage of the well-established herb St. John's wort for treatment of mild to moderate depression; however, reports have suggested the herb has life-threatening potential when used in conjunction with certain drugs.

St. John's wort interferes with the heart drug digoxin and the blood-thinning drug coumadin, according to evidence presented at the Annual Congress for Clinical Pharmacology in Berlin, which supports early warnings by David Kroll, Ph.D. of Pharmacology and senior editor of ( Because slight changes in the activity of these two drugs could have serious health consequences, potential interactions with St. John's wort are particularly worrisome.

The Feb. 12 issue of Lancet revealed the following potentially harmful affects of St. John's wort:

  • St. John's wort can interfere with the effectiveness of protease inhibitors used for treatment of HIV infection.

  • St. John's wort appears to have contributed to heart transplant rejection by interfering with the drug cyclosporine.

  • St. John's wort may decrease the effectiveness of oral contraceptives.

  • St. John's wort affects the body's metabolism of drugs in more than one way, leading to a risk of interactions with numerous medications.

"I recommend individuals taking medication critical to their health should avoid using St, John's wort except on physician advice," says Dr. Steven Bratmen, medical director for "Furthermore, this new information reminds us 'safe natural products' are not always entirely safe. Harmful drug interactions are probably the most likely area for problems to develop."

While an extensive monitoring system exists for drug/drug interactions, the current system for detecting herb/drug interactions is not well developed. Germany has long been praised as a leader in this field, but it is interesting to note while St. John's wort has been widely used there for a decade, German authorities have recorded no reports of drug interactions, according to

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