Steven Foster, one of the most respected names in herbal medicine, is author of 13 books, including 101 Medicinal Herbs (Interweave Press).
St. John's wort has been in the news regarding its effect on birth control pills. What's up?
Foster: St. John's wort has been reported to reduce the effectiveness of birth control pills and other steroidal drugs by interacting with the same cell receptors as steroidal drugs. In a recent study, researchers at the University of Cambridge in England found that St. John's wort competes with steroidal drugs like birth control pills to bind to certain cells (Journal of Endocrinology, 2000, vol. 166). This chemical binding is necessary for the drug to work: If St. John's wort is occupying a certain percentage of those sites, the pill's effectiveness is reduced. It's best to avoid use of St. John's wort while taking birth control pills, or work with your physician to adjust the dose appropriately.
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