FOR IMMEDIATE RELEASE
CONTACT: Robert S. McCaleb
(303) 449-2265
New Study Challenges Assumptions about St. John's Wort Drug
Interactions
July 12, 2000: A groundbreaking new clinical study calls
into question recent warnings about potential interactions between
St. John's wort and prescription drugs, including birth control
pills. The new study, published in Life Sciences, showed
that there were no drug interactions in people who took St. John's
wort along with the anti-anxiety drug alprazolam (Xanax®)
and dextromethorphan, a cough suppressant. These results refute
a common but unproven assumption about St. John's wort - that
the herb reduces the effectiveness of many prescription drugs
because it is metabolized through the same pathway in the liver
(the cytochrome P-450 system). Another significant finding of
the study was the fact that St. John's wort did not interfere
with 3A4, the liver enzyme used to metabolize birth control pills
and other common drugs.
The new study is important because it is the first to examine
St. John's wort metabolism in the human body instead of the test
tube. The researchers pointed out that laboratory (in vitro)
studies have "inherent limitations" that make it difficult
to generalize results to human beings. "The publication of
this study in Life Sciences highlights the danger of issuing
public warnings about herbs based solely on in vitro evidence.
It can be very misleading to extrapolate results from the test
tube to the clinical realm," commented Rob McCaleb, President
of the Herb Research Foundation in Boulder, CO.
No studies have yet tested the effects of St. John's wort in
women taking birth control pills. One small study recently found
that St. John's wort affected blood concentrations of indinavir,
a drug used to treat HIV infection. Both the alprazolam study
and the indinavir study had very small sample sizes of less than
10 people. In the interest of good science, researchers caution
that it is difficult to make conclusions about herb safety - either
negative or positive - based on small, preliminary studies. Clearly,
more research is needed in the evolving science of herb-drug and
food-drug interactions.
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