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No St. John's wort herb/drug interactions in latest research

by Rob McCaleb

Remember all the fuss last year about herb/drug interactions with St. John's wort? This subject led to exaggerated warnings from the medical community and regulators and became the number one question asked of HRF by the press. Much of the speculation was based on a single study led by Dr. Stephen Piscitelli of the National Institutes of Health that showed that SJW speeded up the liver's metabolism of the immune suppressant cyclosporine (for organ transplant patients) and the protease inhibitor indinavir (for HIV/AIDS). This, he claimed, happened because SJW increased the activity of the liver enzyme system that clears these and many other drugs from the bloodstream. Because this enzyme system also metabolizes birth control pills, Dr. Piscitelli did a talk show tour to promote his theory about the "miracle babies" that could result if St. John's wort caused birth control failures. There was never any direct support for this speculation.

Surprise. The latest study by the same research team revealed that SJW did not affect the metabolism of carbamazapine, an anticonvulsant drug metabolized by the very same enzyme system. The bottom line? SJW has been shown to speed the metabolism of indinavir and cyslosporine. But the latest research fails to support the theory that it could interact with carbamazapine. This finding calls into question whether SJW could interact with birth control pills or any of the dozens of other drugs metabolized by this pathway.

Burstein AH, Horton RL, Dunn T, et al. Lack of effect of St. John’s wort on carbamazepine pharmacokinetics in healthy volunteers. Clinical Pharmacology and Therapeutics 2000; 68: 6.

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