St.John’s Wort–The P450 Superwoman


St. John’s Wort is a widely used botanical that has many interactions with commonly prescribed medications.  In fact the the United States Food and Drug Administration issued a  health advisory about St. John’s Wort.

St. John’s Wort increases the level of enzyme system in the liver called the P450 system.  In medical school, the P450 system seemed to be the super enzyme that accomplished everything–wife, mother, powerful leader –oh sorry, that was Condeleeza Rice…Actually the P450 is responsible for breaking down many toxins in the body.  If you are interested in trivia, or in taking my medical school biochemistry tests for me, you would be interested to know that St. John’s Wort induces the cytochrome P450 isoenzymes CYP3A4, CYP2C9, CYP1A2 and the transport protein P-glycoprotein.  When these cytochrome P450 enzyme levels are increased, the breakdown of certain medicines is enhanced.  These medications include warfarin, cyclosporine, digoxin, theophylline, HIV protease inhibitors and birth control pills.  So blood concentrations of these medications may be decreased if you are also taking St. John’s Wort. 

Make sure you discuss St. John’s Wort or ANY supplement or herbal remedy you may be taking with your doctor.  It may be that the levels of other medicines you are taking may be higher or lower than desired because of interactions with St. John’s Wort.
Last Updated March 24, 2010

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