Herbal Remedies in the United States: Potential Adverse Interactions With Anticancer Agents Alex Sparreboom, Michael C. Cox, Milin R. Acharya, and William D. Figg A B S T R A C T Purpose Interest in the use of herbal products has grown dramatically in the Western world. Recent estimates suggest an overall prevalence for herbal preparation use of 13% to 63% among cancer patients. With the narrow therapeutic range associated with most anticancer drugs, there is an increasing need for understanding possible adverse drug interactions in medical oncology. Methods In this article, a literature overview is provided of known or suspected interactions of the 15 best-selling herbs in the United States with conventional allopathic therapies for cancer. Results Herbs with the potential to significantly modulate the activity of drug-metabolizing enzymes (notably cytochrome P450 isozymes) and/or the drug transporter P-glycoprotein include garlic (Allium sativum), ginkgo (Ginkgo biloba), echinacea (Echinacea purpurea), ginseng (Panax ginseng), St John’s wort (Hypericum perforatum), and kava (Piper methysticum). All of these products participate in potential pharmacokinetic interactions with anticancer drugs. Conclusion It is suggested that health care professionals and consumers should be aware of the potential for adverse interactions with these herbs, question their patients on their use of them, especially among patients whose disease is not responding to treatments as expected, and urge patients to avoid herbs that could confound their cancer care. J Clin Oncol 22:2489-2503. INTRODUCTION In recent years, interest in complementary and alternative medicine (CAM) has grown rap- idly in the industrialized world. The National Center for Complementary and Alternative Medicine defines CAM as a group of diverse medical and health care systems, practices, and products not considered part of conventional medicine. Biologically based therapies in CAM use substances found in nature, such as herbs, foods, and vitamins. Herbal remedies include dietary supplements (any product other than tobacco intended for ingestion as a supplement to the diet, including vitamins, minerals, antioxidants, herbal products, me- tabolites, and other products), phytomedicine (the use of plants or plant parts to achieve a therapeutic effect), and botanical medicine or phytomedicine (botanic supplements used as medicine). Factors contributing to this increase are dissatisfaction with con- ventional allopathic therapies, patients’ desire to be more active in their own health care, and patients’ philosophical orientations. 1,2 It is estimated that up to one third of the entire population in the United States used CAM in the last 12 months; the majority of those individuals use herbal products on a routine basis. 3-5 An estimated 15 million adults combined herbal remedies with prescription medi- cations, with more recent estimates put- ting this figure at approximately 16%. 6-8 With a larger number of the population using herbal treatments, combined with allopathic therapies, the risk for herb- drug interactions is a growing concern. From the Clinical Pharmacology Re- search Core, Medical Oncology Clinical Research Unit, Center for Cancer Re- search, National Cancer Institute, Be- thesda, MD. Submitted August 27, 2003; accepted December 2, 2003. Address reprint requests to Alex Sparreboom, PhD, Clinical Pharmacol- ogy Research Core, Medical Oncology Clinical Research Unit, National Cancer Institute, 9000 Rockville Pike, Bldg 10, Room 5A01, Bethesda, Maryland 20892; e-mail: sparreba@mail.nih.gov. 0732-183X/04/2212-2489/$20.00 DOI: 10.1200/JCO.2004.08.182 JOURNAL OF CLINICAL ONCOLOGY R E V I E W A R T I C L E VOLUME 22  NUMBER 12  JUNE 15 2004 2489