Recent findings that the widely-used herbal supplement Saint John's wort could dramatically affect the absorption and metabolism of many prescription and non-prescription drugs raised concerns that other popular herbal supplements might cause similar changes, thus significantly altering drugs' therapeutic or toxic effects.
What, for example, about ginseng and ginkgo biloba, two of the most widely used herbal supplements in this and other countries?
Speaking on May 1 at Experimental Biology 2007, University of Kansas Medical Center scientist Dr. Gregory Reed reports a study that found daily use of ginseng or ginkgo biloba supplements at the recommended doses, or the combination of both supplements, are unlikely to alter the pharmacokinetics - by which drugs are absorbed, distributed, metabolized, and eliminated by the body - of the majority of prescription or over-the counter drugs. Dr. Reed's presentation was part of the scientific program of the American Society for Pharmacology and Experimental Therapeutics.
The research team, led by Dr. Reed and the late Dr. Aryeh Hurwitz, recruited 72 healthy non-smoking adults (31 men and 41 women, ages 20 to 59) who were not taking any prescription drugs or dietary supplements. The participants were given a "cocktail" of five drugs, each drug in the cocktail chosen because it provides a measure of the activity of a key drug metabolism pathway. Taken together, the five drugs in the cocktail provide measurements of the pathways that determine the pharmacokinetics of over 90 percent of prescription drugs. The scientists then measured the presence of these drugs or their metabolites in each subject's blood and urine in order to establish a baseline for how each individual absorbed and metabolized the different prescription drugs in the absence of herbal supplements.
The 72 individuals next were randomly assigned to one of four groups. For four weeks, the first group received a ginseng supplement and a placebo for ginkgo biloba; the second received ginkgo biloba and a placebo for ginseng; the third received both ginseng and ginkgo biloba supplements; and the fourth received placebos for both supplements. The prescription drug cocktail was again administered and blood and urine samples taken in order to determine the absorption and metabolism of these drugs in the presence of either or both of the herbal supplements.
The scientists found no significant differences between those who received one, both, or none of the ginseng and ginkgo biloba supplements in how their bodies absorbed or metabolized any of the five prescription drugs. This suggests, says Dr. Reed, that neither ginseng nor ginkgo biloba will affect the pharmacokinetics of the majority of prescription or over-the counter drugs. He does note, however, that the team did not investigate any possible effects of the herbal supplements on pharmacodynamic interactions: the way drugs produce desired therapeutic effects or cause adverse side effects. The possibility of these pharmacodynamic, as opposed to pharmacokinetic, interactions remains to be investigated.
Studies in Dr. Reed's laboratory continue with an examination of the effects of Saint John's wort on pharmacokinetics of prescription and non prescription drugs and the role of an individual's genetic makeup in determining the magnitude of the herbal supplement's effects. This work was supported by the National Center for Complementary and Alternative Medicine of the National Institutes of Health.