St. John's wort weakens punch of cancer drug

SAN FRANCISCO -- St. John's wort appears to interfere powerfully with a common cancer drug and can reduce its punch for weeks after people stop taking the herbal supplement, a study shows.

St. John's wort is often taken as an over-the-counter remedy for mild depression, though its effectiveness has been questioned. Doctors also know the herb can interfere with the body's use of a variety of other medicines.

In a small study released Monday, doctors showed that St. John's wort decreases blood levels of one chemotherapy drug by about 40 percent. This effect lingered for more than three weeks after people stopped taking the supplement.

Dr. Ron Mathijssen of the Rotterdam Cancer Institute in the Netherlands, who directed the study, said St. John's wort could reduce the ability of chemotherapy to knock down cancer.

"People don't realize it is a drug because you don't need a prescription. People think it's harmless," he said.

Mathijssen presented the results of the study, conducted on five patients, at a meeting in San Francisco of the American Association for Cancer Research.

Despite the small size of the study, experts said the findings are believable because they fit with earlier reports showing that St. John's wort can disrupt drug treatment.

In the latest study, researchers tested the interaction of St. John's wort with Camptosar, a medicine used to treat many kinds of cancer.