The effect of herbal medicines on platelet function: an in vivo experiment and review of the literature.

Background: Herbal medicines are used by a considerable number of surgical patients. An increased risk of bleeding, substantiated by anecdotal reports, has been attributed to the use of certain herbs, and numerous in vitro experiments have identified some herbal extracts as platelet inhibitors. The purpose of this investigation was to determine whether standard commercial preparations of commonly used herbal medicines have an effect on platelet function in vivo and, by extension, to provide clinical scientific evidence of the safety of their use in the perioperative period.

Methods: Five commercially available herbal agents were investigated, including Ginkgo biloba, garlic, Asian ginseng, St. John's wort, and saw palmetto. In a blinded fashion, one of the agents was administered to 10 adult volunteers at the manufacturer's recommended dose for 2 weeks. At the end of the 2-week period, in vivo platelet function was quantified using the PFA-100 assay. After a 2-week "washout" period, the protocol was repeated using a different agent. This 4-week cycle was repeated for each of the five herbal agents, as well as the control agent aspirin.

Results: In vivo platelet function was not affected by the administration of any herbal agent and was markedly inhibited with the administration of aspirin.

Conclusions: The herbal medicines investigated in this study do not affect platelet function in vivo. Neither this experiment nor a review of the literature supports the concern of perioperative bleeding in users of these herbal medicines.