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Cancer patients and survivors should discuss supplement and vitamin use with their oncologists.
When discussing herbal medicines, Brian Lawenda, MD, reminds patients that many drugs are derived from plants and fungi—so despite any gentle and appealing packaging, herbal medicines can be powerful substances with the potential to interfere with life-saving cancer treatment.
“We have a lot of data that show drug-herb interactions,” says Lawenda, clinical director of 21st Century Oncology in Las Vegas and a Harvard-trained radiation oncologist who integrates complementary approaches with conventional cancer treatment. “Some botanical products can make people more susceptible to bleeding,” he says. “There are also a fair number that can decrease the efficacy of chemotherapy or increase toxicity.”
For example, because of the way it acts in the body, the popular herb St. John’s wort may actually decrease the effectiveness of transplant drugs (for example, cyclosporine and tacrolimus) and forms of chemotherapy (irinotecan, for example). High amounts of garlic may have several effects, which include interfering with the metabolism of some drugs and decreasing the blood’s ability to clot.
Above all, Lawenda and others say, it’s important for patients to talk to their physicians or some member of their medical care team about herbs or botanical products they may be taking. Most herbs have not been studied rigorously, and given the theoretical risk, doctors generally discourage their use. However, Lawenda says, most doctors are willing to discuss the pros and cons.
“I usually ask, ‘Do you want me to go through these things with you and talk about the data?’” he says. Beyond the one-on-one, he encourages accessing online resources, such as the integrative medicine site at Memorial Sloan-Kettering Cancer Center, which has a searchable “About Herbs” database (mskcc.org/mskcc/html/11570.cfm).
Another resource to look up common herb—drug interactions is the American Cancer Society herb information site. Visit cancer.org and type “herbs” in the search box. The National Center for Complementary and Alternative Medicine has information on herbs at nccam.nih.gov/health/herbsataglance.htm.
View Chart: Potential Drug - Supplement Interactions