St. John's Wort is an herb commonly used around the world as a "natural" treatment for depression. Just because it is "natural" doesn't mean it doesn't have risks when it comes to treating cancer patients, according to an article and editorial in the August 21 issue of the Journal of the National Cancer Institute (Vol. 94: 1247-1249; 1187-1188).

The research, conducted in the Netherlands, was based on previous observations that St. John's Wort increases levels of certain enzymes in the body. In turn, these enzymes can cause common drugs in the body to be processed more quickly than normal, weakening their effect. The researchers wondered if St. John's Wort might also be decreasing the blood level of a patient's chemotherapy during cancer treatment.

Because a drug called irinotecan, which is a commonly used and effective treatment of cancer, is processed through one of these enzyme systems, R. H. J. Mathijssen and his colleagues from the department of medical oncology at the Daniel den Hoed Cancer Center in Rotterdam, examined whether St. John's Wort decreased the amount of irinotecan in the bodies of patients who were taking the chemotherapy drug.

The researchers examined blood levels of irinotecan in five patients who received the chemotherapy either with or without previous treatment with St. John's Wort.

When the patients were given St. John's Wort, the amount of irinotecan in the blood was decreased by 42%.

That means the patients received less drug than needed to treat the cancer properly.

The researchers also found that the reduction in the drug levels was greater the longer the patients had been taking St. John's Wort.

"Overall, our findings suggest that irinotecan metabolism and toxicity are altered by St. John's Wort and that the two agents cannot be given safely in combination without compromising overall antitumor activity," wrote the authors.

They concluded that "until specific dosing guidelines are available, it is strongly recommended that patients receiving chemotherapeutic treatments with such agents refrain from taking St. John's Wort."

In an editorial that accompanied the article, Patrick J. Mansky, MD, and Stephen E. Straus, MD, from the National Center for Complementary and Alternative Medicine at the National Institutes of Health in Bethesda, Md., echoed the concerns of the study's authors.

"That herbal medicines may have adverse pharmacologic properties has come as a surprise to those who assumed that natural products must be safe," wrote Mansky and Straus. "Yet," they continued, "for products (be they synthetic drugs or complex herbal mixtures) to convey beneficial physiologic effects, we understand that the biochemical constituents in them must also harbor the risk for adverse effects."

St. John's Wort is not the only herbal remedy that can affect the way the body handles drugs, they noted. Recent reports found that four of the seven top-selling herbal medicines, including ginkgo, ginseng, garlic, and kava can alter the way a patient responds to such commonly used drugs as diuretics, blood-thinners, and tranquilizers.

St. John's Wort has also affected the levels of drugs used to treat patients with HIV infection and those receiving transplants, resulting in resistance to treatment and rejection of transplanted organs, according to the editorial.

"With increased availability in the American marketplace and increased public consumption of herbal medicines over the past decade, however, the specter of herb-drug interactions has emerged as a credible public health problem," wrote Mansky and Straus.

They noted that cancer patients and their doctors must be aware that no matter how helpful some herb treatments may appear, they are not all safe. "Together, patients and oncologists should consider the options and develop a plan regarding which complementary and alternative medicine practices to pursue and which to put aside altogether."

Major cancer centers such as Memorial Sloan-Kettering Cancer Center in New York have been aware of the problems with herbal treatments for some time.

Barrie Cassileth, MD, who is the chief of Memorial's integrative medicine service and a member of the American Cancer Society's alternative and complementary methods of cancer management advisory group, said the message is clear.

"We have to be careful about taking botanicals with radiation therapy, surgery, and chemotherapy," said Cassileth. "At Memorial, we tell our patients to stop all herbal remedies for two weeks before treatment."

Cassileth makes the point that when they started looking at the question of the effects of herbal remedies on cancer treatments, they also found that the problem pertained to any major medication.

Cassileth stressed the importance of doctors, nurses, and other health care workers telling patients about the need to stop herbal remedies before receiving treatments or undergoing surgery. "We tell patients to stop aspirin and vitamin E. We should also tell them to stop herbal remedies," she said.

Herbs are really dilute pharmaceuticals, Cassileth emphasized. That doesn't mean they are bad. Many herbs have beneficial effects. But they can also cause harm if not used properly.

What's important to remember, concluded Cassileth, is that these recommendations are not the result of a bias against herbal remedies.

"This is a crucial issue, and the recommendations we make are based on hard data," she said. "Herbs can be helpful, but they can also be very harmful."