The majority of cancer patients use complementary therapies such as herbs and dietary supplements. Although figures differ, surveys indicate that as many as 60 percent of people with cancer take two or more dietary supplements daily.
In this Grand Rounds presentation, K. Simon Yeung, a pharmacy and botanicals specialist with Memorial Sloan Kettering’s Integrative Medicine Service, details potential negative interactions between herbs (dietary supplements) and some of the drugs used in cancer treatment. After addressing the history and prevalence of herbal and dietary supplement use among cancer patients in the United States, he outlines the common mechanisms underlying risks for interactions. Various herbs can affect drug absorption and metabolism, for example, which can in turn increase or decrease the effectiveness and toxicity of various medicines. Dr. Yeung touches on the cancer drugs most prone to these interactions, and discusses the importance of healthcare providers in asking patients about complementary medicine use. Foods and botanicals that commonly interact with cancer drugs include grapefruit juice, St. John's wort, ginkgo, and kava kava. Common cancer therapies that may be made more or less effective or toxic due to an herb-drug interaction include tyrosine kinase inhibitors, warfarin, tamoxifen, and immunosuppressants. Doctors should monitor patients closely if they are receiving cancer drugs and taking herbs, Dr. Yeung advises, and make adjustments to the drug dose or route of administration if needed.