Planta Med 2011; 77(4): 311-321
DOI: 10.1055/s-0030-1250457
© Georg Thieme Verlag KG Stuttgart · New York

Effects of Herbal Supplements on Drug Glucuronidation. Review of Clinical, Animal, and In Vitro Studies

Mohamed-Eslam F. Mohamed1 , Reginald F. Frye1
  • 1Department of Pharmacotherapy and Translational Research, College of Pharmacy, University of Florida, Gainesville, Florida, USA
Further Information

Publication History

received June 29, 2010 revised Sept. 7, 2010

accepted Sept. 29, 2010

Publication Date:
03 November 2010 (online)


The use of herbal supplements has increased steadily over the last decade. Recent surveys show that many people who take herbal supplements also take prescription and nonprescription drugs, increasing the risk for potential herb-drug interactions. While cytochrome P450-mediated herb-drug interactions have been extensively characterized, the effects of herbal extracts and constituents on UDP-glucuronosyl transferase (UGT) enzymes have not been adequately studied. Thus, the purpose of this review is to evaluate current evidence on the glucuronidation of phytochemicals and the potential for UGT-mediated herb-drug interactions with the top-selling herbal supplements in the United States and Europe. In vitro and animal studies indicate that cranberry, Ginkgo biloba, grape seed, green tea, hawthorn, milk thistle, noni, soy, St. John's wort, and valerian are rich in phytochemicals that can modulate UGT enzymes. However, the in vivo consequences of these interactions are not well understood. Only three clinical studies have investigated the effects of herbal supplements on drugs cleared primarily through UGT enzymes. Evidence on the potential for commonly used herbal supplements to modulate UGT-mediated drug metabolism is summarized. Moreover, the need for further research to determine the clinical consequences of the described interactions is highlighted.


Dr. Reginald F. Frye, Associate Professor

Department of Pharmacotherapy and Translational Research
College of Pharmacy
University of Florida

P. O. Box 100486

Gainesville, FL 32610


Phone: +1 352 273 5453

Fax: +1 352 273 6121