St. John's Wort Reduces Effectiveness of Anticancer Medication, UB Study Shows

BUFFALO, N.Y. -- The herbal supplement St. John's Wort has been shown to undermine the effectiveness of a newer, revolutionary anticancer medication, according to a study by University at Buffalo researchers.

The study, forthcoming in the November issue of the journal Pharmacotherapy, is the first to show that St. John's Wort may compromise the effectiveness of Gleevec® (imatinib mesylate, Novartis, Inc.), a blockbuster anticancer drug that has revolutionized the treatment of chronic leukemia, according to Patrick F. Smith, assistant professor in the School of Pharmacy and Pharmaceutical Sciences.

The study is especially timely because recent surveys show that the use of alternative supplements such as St. John's Wort has increased tremendously over the past decade, particularly among cancer patients, Smith said. Approximately one-third to one-half of all cancer patients utilize some type of alternative supplement, such as vitamins and herbal products, according to the study.

"We found that St. John's Wort may significantly reduce the effect of Gleevec® by lowering blood levels to the point where patients may fail therapy if they take both together," Smith said.

"Patients may not view alternative products as 'medications,' and thus they frequently go unreported to the patient's physician or pharmacist," Smith said. "For the most part, patients often times don't necessarily need these herbal products, and don't know that there may be serious drug interactions."

Gleevec®, or imatinib mesylate, was the first drug to specifically target cancer cells without targeting normal cells, making it relatively non-toxic, unlike traditional chemotherapy drugs. And it's easier to take: while chemotherapy is administered intravenously every few weeks for several dosing cycles, Gleevec® is taken in a daily, oral dose over the course of years.

"Hence, it is the first drug that turns cancer into a chronic disease that is treated with a tablet, similar to high blood pressure or diabetes," Smith said.

As a result, Gleevec received an expedited approval in the United States for the treatment of chronic myeloid leukemia (CML) and has become rapidly a cornerstone of cancer treatment, according to Smith.

Taking St. John's Wort, commonly used for mood elevation in cancer patients, along with Gleevec® "will unnecessarily put patients at risk for failure and resistance during treatment," Smith said. That's because the St. John's Wort increases a patient's metabolism of the medication, resulting in the drug's being eliminated more quickly than normal from the body. This lowers the blood levels, or reduces the patient's exposure, to the medication, decreasing its effectiveness.

"Thus, the reduction in blood levels caused by St. John's Wort may cause Gleevec® to be less effective, resulting in treatment failure. The other thing that can happen is that, if blood levels are too low, the leukemia cells also can become resistant to Gleevec®, rendering it completely ineffective, even if the dose is increased," Smith explained.

Similar results have been described in drug interaction studies of St. John's Wort with medications for AIDS, said Smith, who added that he believes cancer patients should avoid herbal supplements in general during treatment.

"We need to do a better job of educating both physicians, as well as the public, regarding the hazards of taking these herbal products, which are unregulated by the FDA," Smith said.

"It is imperative that patients know that herbals are not regulated and that they may be very dangerous when combined with certain drugs. Patients should always check with their physician or pharmacist before taking any herbal or over the counter product. Their lives literally may depend on it."

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