Ginseng, ginkgo don't interfere with drug absorption

NEW YORK, May 2 (Reuters) 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 per cent 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 yesterday at a meeting of the American Society for Pharmacology and Experimental Therapeutics, part of Experimental Biology 2007.

REUTERS SYU DS1052