Probe drug investigations suggest no pharmacokinetic interactions with ginseng and ginkgo biloba supplements

Interactions between herbal supplements and drugs, as demonstrated for Saint John’s wort, can dramatically affect the safety and efficacy of drugs. We have completed a randomized, double‐blind clinical study of potential pharmacokinetic interactions with ginseng and ginkgo biloba, two of the most widely used herbal supplements, using a probe drug cocktail approach. The cocktail employed contained the following drugs (and probed the following activities): caffeine (CYP1A2), losartan (CYP2C9), dextromethorphan (CYP2D6), buspirone (CYP3A4), and fexofenadine (P‐glycoprotein). We recruited 72 healthy non‐smoking adults and randomized them to four arms: ginseng and ginkgo supplements, ginseng and placebo for ginkgo, ginkgo and placebo for ginseng, and double placebo. Each subject was screened for baseline activities using the probe drug cocktail, and then was again screened following 4 weeks of treatment with herbs and/or placebos. One‐way Analysis of Variance (ANOVA) using Dunnett’s procedure was used to compare each of the three treatments with the control. We found no significant differences between the treatment groups in any of the measured probe drug parameters. Our observations suggest that daily use of ginseng or ginkgo biloba supplements, or the combination of both supplements, will not alter the pharmacokinetics of the majority of prescription or over‐the‐counter drugs. This work was supported by 5R01 AT‐000842, awarded by NCCAM to A.H.