A Comprehensive Review of Recent Studies on Herb-Drug Interaction: A Focus on Pharmacodynamic Interaction

Objectives: The concomitant use of herbal and conventional drugs accelerates the possibility of clinically significant herb-drug interactions (HDIs). This paper aims to analyze the current status of HDI studies worldwide and to review studies on HDI-induced pharmacodynamic (PD) interactions. Methods: HDI studies published from 2000 to 2014 and indexed in PubMed were categorized according to publication year, area/country, study methods and objectives, and disease categories. The reviewed studies focused on HDI-induced PD; each PD interaction with concurrent use of approximately 100 herbal drugs and 70 conventional drugs was summarized. All PD-related articles were categorized according to four characteristics: herbal drugs, conventional drugs, types of PD interaction, and type of study. Among them, 17 well-designed clinical studies were evaluated by using the Jadad Quality Assessment Scale. Results: The number of HDI reports has gradually increased since 2000, with a primary focus on neoplasms and diseases of the circulatory system. Most of these investigated pharmacokinetic reactions, such as cytochrome P450 enzyme metabolism, with fewer reports investigating PD. Most PD interaction studies investigated warfarin, ginkgo leaves, and St. John's wort. An evaluation of 17 studies revealed a generally positive view of PD effects involving synergism or reduced toxicity and a high average quality score (>3 points on a 0-5 scale). Conclusions: These results demonstrate that most HDI studies so far have examined PK interactions and have been limited to very few conventional drugs and herbal drugs. This suggests that more studies focusing on PD are necessary to understand interactions between commonly used herbal and conventional drugs.