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Study: St. John’s Wort Interferes With Chemotherapy (dateline January 11, 2003)

St. John’s Wort, a popular over-the-counter herbal remedy used to treat depression, appears to interfere with chemotherapy, decreasing the effectiveness of the cancer treatment, according to a recent report in the Journal of the National Cancer Institute. In the study, St. John’s Wort weakened the effect of the common chemotherapy drug irinotecan. The study underscores the importance of communication between patients and physicians and also shows that herbal remedies may have adverse effects, particularly when combined with other treatments.

St. John’s Wort (botanical name, hypericum perforatum) is an herbal supplement sold without a prescription in the United States. It has been used to treat mild to moderate depression and other conditions including anxiety, stomach upset, insomnia, fluid retention, and hemorrhoids. Common side effects to St. John’s Wort include increased skin sensitivity to sunlight, rash, a feeling of fullness in the stomach, and constipation. There are no solid data to suggest that St. John’s Wort is clinically effective at treating depression, though studies at the National Institute of Mental Health and other agencies are currently underway to help better understand the herbal remedy.

Since St. John’s Wort has been suggested to interfere with chemotherapy, Alex Sparreboom, PhD and colleagues from Erasmus MC–Daniel den Hoed Cancer Center in Rotterdam, The Netherlands, studied the effect of St. John’s Wort in patients treated with the chemotherapy drug irinotecan. Irinotecan (brand names, Camptosar, Camptothecan-11, CPT-11) is a common chemotherapy drug used to treat several types of cancer, including colon cancer and some lymphomas.

The five cancer patients in the study were randomly assigned to receive either St. John’s Wort with chemotherapy or no additional herbal treatment. Dr. Sparreboom and his team then measured the blood levels of the chemotherapy drug irinotecan in all patients after treatment. The result: in patients who received St. John’s Wort in addition to chemotherapy, the amount of irinotecan in the blood was reduced by 42%. Thus, St. John’s Wort prevented these patients from receiving adequate amount of the chemotherapy drug to effectively treat their cancer.

St. John’s Wort is thought to interfere with chemotherapy by increasing the levels of certain enzymes in the body. Since chemotherapy drugs such as irinotecan are processed by the same enzymes, the cancer drugs become processed more quickly than normal when St. John’s Wort is also in the patient’s system. Thus, Dr. Sparreboom and his colleagues recommend that until further data are available on St. John’s Wort, patients should not take the herb if they are receiving chemotherapy with irinotecan.

The American Cancer Society reports that ginkgo, ginseng, garlic, and kava can also change the way in which patients respond to treatments with diuretics, blood-thinners, and tranquilizers. In addition, St. John’s Wort has also been found to interfere with drugs used to treat patients with HIV and those receiving organ transplants. Patients have become resistant to treatment or actually rejected transplants due to St. John’s Wort, according to an editorial by Patrick J. Mansky, MD, and Stephen E. Straus, MD, of the National Center for Complementary and Alternative Medicine. The editorial was also published in the Journal of the National Cancer Institute.

Alternative and complementary medicines have become increasingly popular in recent years. Though some herbal or "natural" treatments can be beneficial, it is important for patients to realize that not all alternative or complementary medicines are safe. Patients who are considering non-traditional medicines should thoroughly investigate the therapy and consult with their physicians or alternative medicine practitioners to make sure the therapy is safe and will not interact with other medicines they may be taking.

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