Ginseng and ginkgo don't interfere with drug absorption
May 1, 2007
By Megan Rauscher
NEW YORK (Reuters Health) - Ginseng and ginkgo biloba fans may be
relieved to learn that these two popular herbal supplements don't seem to
alter how most prescription and over-the-counter drugs are absorbed or
metabolized in the body, unlike other herbs such as Saint John's Wort.
The effects of prescription and over-the-counter drugs depend on the
properties of the drug, how much drug enters the body, and on how long the
drug stays in the body. The latter two properties are called drug
"pharmacokinetics."
"Saint John's Wort," Dr. Gregory A. Reed told Reuters Health, "is an
example of an herbal supplement that dramatically alters the
pharmacokinetics of many drugs."
"A person taking Saint John's Wort daily will metabolize and clear drugs
from their system much more rapidly than normal," making it less likely that
enough drug will get into the patient after a "normal dose" or that the drug
will be retained in the body long enough to exert therapeutic effects, he
explained.
This doesn't seem to be the case for ginseng and ginkgo biloba, according
to Reed's study of 72 healthy adults. The volunteers, who were not taking
any prescription drugs or dietary supplements, were given a combination of
five drugs that, when taken together, yield information on the
pharmacokinetics of over 90 percent of prescription drugs.
Reed, from University of Kansas Medical Center, and colleagues measured
the levels of drugs or their metabolites in each subject's blood and urine
to establish how each individual absorbed and metabolized the different
drugs in the absence of ginseng and ginkgo biloba.
The volunteers were then randomly assigned to one of four groups:
ginseng, ginkgo biloba, both herbs together, or placebo. The volunteers then
took the five-drug combination again and had their blood and urine tested.
There were no significant changes in any of the four treatment groups in
how the prescription drugs were absorbed or metabolized, Reed told Reuters
Health.
"We do not know if ginseng or ginkgo supplements at recommended doses can
alter the effects of specific drugs in a patient, but we have shown that
these herbal supplements do not alter how patients metabolize and clear
drugs," Reed said.
He presented the research Tuesday at a meeting of the American Society
for Pharmacology and Experimental Therapeutics, part of Experimental Biology
2007.
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