| Herb Research Foundation
| 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.
Johns wort on carbamazepine pharmacokinetics in healthy
volunteers. Clinical Pharmacology and Therapeutics 2000;
© 2000 by Herb Research Foundation,
Boulder, CO, USA.