• 4/1/2004
  • Florida
  • Sid Kirchheimer
  • WebMD Medical News

There’s more bad news for St. John’s Wort, once the darling of herbal remedies and still the world’s most popular alternative to prescription antidepressants: A new study now indicates that the herbal medicine compromises a powerful cancer-fighting drug used to treat a form of blood cancer.

At least six previous studies show that the reason for this effect is the same: The over-the-counter supplement causes higher levels of a particular substance to be made that the body uses to breakdown other disease-fighting medicines. This time, St. John’s Wort was found to interfere with Gleevec, a powerful drug that targets only cancerous cells and is used to treat people with leukemia. The drug is currently taken daily to normalize the large numbers of abnormal white blood cell in leukemia patients. However, Gleevec is being tested — and showing promise — in treating other aggressive cancers. “We found that when St. John’s wort is taken in combination with Gleevec, it caused the amount of Gleevec in the blood to drop by 30%,” says researcher Reginald F. Frye, PhD, of the University of Florida Center of Pharmacogenomics. “That may not sound like much, but for Gleevec, a 30% reduction is very important.

He says that there is a critical blood level of the drug that leukemia patients need to be above to prevent the disease from coming back, what is known as a disease relapse. “What this study shows is that if they took St. John’s Wort, they fell below that threshold for one-third of the day,” he tells WebMD. “If they didn’t take St. John’s Wort, they stayed above the danger threshold for the entire day. St. John’s Wort was enough to cause a relapse.”

Frye’s study, which will be presented Saturday before the American Society for Clinical Pharmacology and Therapeutics, involved 12 healthy, cancer-free volunteers. Each took a standard dose of Gleevec. The researchers then looked at the blood levels of Gleevec over three days. For the next two weeks, they took 300 milligrams of St. John’s Wort three times a day; on the 15th day, they were given another dose of Gleevec and their blood was tested again to check the blood levels of the cancer-fighting drug. The blood tests showed a marked decrease in Gleevec concentrations following the St. John’s Wort, indicating the herb causes Gleevec to be depleted faster.

In recent years, other studies have indicated that St. John’s Wort has a similar effect on birth control pills, prescription blood-thinners, antidepressants, blood pressure medications, drugs taken following organ transplants, and on patients with HIV and AIDS. It’s also been found to reduce the efficacy of another cancer-fighting drug called Camptosar. Interestingly, most of these studies came after the FDA issued an advisory to doctors four years ago urging them to caution patients about the potential risks of taking St. John’s Wort along with other medications.

Most recently, a study six months ago in the Journal of the American Medical Association suggested that taking St. John’s Wort can reduce the effectiveness of up to half of all prescription and over-the-counter drugs. In most cases in this previous research, the same mechanism is cited as with Frye’s study: St. John’s Wort causes a dramatic effect on one of various substances that the body uses to breakdown medications.

“Basically, St. John’s Wort causes the body to produce more of that enzyme, and it’s the job of this enzyme to deplete drugs from the blood at a quicker rate,” Frye tells WebMD. In past studies, some disease-fighting drugs were eliminated from blood twice as quickly after patients took St. John’s Wort as compared to when they didn’t.
St. John’s Wort has been used for centuries for a variety of conditions — from treatment for malaria to a balm for burns, reports the National Center for Complementary and Alternative Medicine. Today, it’s mostly used for mild-to-moderate depression, anxiety, and sleep problems, and is used in Europe more often than prescription drugs for these conditions. St. John’s Wort remains among the top-selling herbal products in the U.S., but sales have dipped since the drug-interfering studies started to emerge — from $310 million in 1998 to $195 million three years later, according to the Nutrition Business Journal.
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SOURCES: Reginald F. Frye, PhD, associate director, Center for Pharmacogenomics, University of Florida, Gainesville. Markowitz, J. The Journal of the American Medical Association, Sept. 17, 2003; vol 290: pp 1500-1504. Mathijssen, R, Journal of the National Cancer Institute, Aug. 21, 2002. Roby C, Clinical Pharmacology Therapy, May 2000; vol 67: pp 451-457. National Center for Complementary and Alternative Medicine web site. Nutrition Business Journal.