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St. John's Wort and Chemo Don't Mix

Herbal Supplement Interferes With Cancer Treatment

WebMD Health News

Aug. 20, 2002 -- Taking St. John's wort during chemotherapy could jeopardize the effectiveness of cancer treatment. A new study shows the popular herbal supplement speeds the metabolism of the chemotherapy drug Camptosar, which compromises its tumor-fighting capabilities.

The study appears in the Aug. 21 issue of the Journal of the National Cancer Institute.

Researchers say surveys show cancer patients are among the most likely to use complementary and alternative medical remedies, such as herbal supplements, in hopes of reducing side effects of conventional treatments or otherwise improving their quality of life.

They say St. John's wort is one of the most popular herbal supplements among cancer patients because of its alleged ability to relieve mild to moderate forms of depression. But past studies have suggested that the supplement can increase levels of an enzyme involved in drug metabolism.

That prompted researcher Ron H. Mathijssen, MD, and colleagues at the Erasmus MC-Daniel den Hoed Cancer Center in the Netherlands to look at the effect of St. John's wort in five cancer patients undergoing treatment with the commonly used chemotherapy drug Camptosar.

The two men and three women were given the standard dose of the anti-cancer drug at two different times -- either alone or after 14 days of treatment with St. John's wort (one 300 mg tablet three times a day). Two of the patients had colorectal cancer, two had lung cancer, and one had sarcoma.

At the end of the study, researchers found that levels of the active ingredient in Camptosar were 42% lower in patients who took St. John's wort during chemotherapy than when they received the chemotherapy alone.

"Our findings suggest that [Camptosar] metabolism and toxicity are altered by [St. John's wort] and that the two agents cannot be given safely in combination without compromising overall antitumor activity," according to the researchers.

They say St. John's wort may also interfere with the effectiveness of other chemotherapy medications that work in similar ways as Camptosar, such as Taxol -- used for ovarian and breast cancer.

Therefore, the study authors caution that "Until specific guidelines are available, it is strongly recommended that patients receiving chemotherapeutic treatments with such agents refrain from taking [St. John's wort]."

In an editorial that accompanies the study, researchers from the National Center for Complementary and Alternative Medicine say both doctors and patients should proceed with caution.

Patrick J. Mansky and Stephen E. Straus say that patients and their doctors need to understand that no matter how beneficial some approaches may appear to be, they are not all safe. They suggest waiting for results of ongoing studies funded by the National Institutes of Health on complementary and alternative medicine.

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