BUFFALO, N.Y., Oct 25, 2004 (United Press International via COMTEX) -- The herbal supplement St. John's Wort undermines the effectiveness of a newer anticancer medication, a study by University at Buffalo researchers says.

The drug, Gleevec, by Novartis, is taken orally as tablets in the treatment of chronic leukemia.

"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," said Patrick Smith, assistant professor in the School of Pharmacy and Pharmaceutical Sciences.

Gleevec was the first drug to specifically target cancer cells without targeting normal cells, making it relatively non-toxic, unlike traditional chemotherapy drugs.

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.

The study will appear in the November issue of the journal Pharmacotherapy.

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