Herb-Drug Interactions Uncommon

Study Shows Few People Taking Dangerous Combos

Medically Reviewed by Salynn Boyles on May 25, 2006

May 25, 2006 – St. John's wort, ginkgo biloba, black cohosh. Just a decade ago most Americans would not have known these names. Today, these and other herbal medications are not only familiar, but the products are fixtures on drugstore shelves.

Herbal remedies are not just for health food stores anymore. The medications have gone mainstream, and as sales continue to rise, so do concerns about their interactions with prescription and more traditional over-the-counter drugs.

But new research suggests that potentially dangerous interactions may occur less often than are widely believed. Investigators reviewed the drugs taken by 7,652, mostly older Canadians, and found very few instances of such interactions.

The findings are to be presented tomorrow in Alberta, Canada, at the North American Research Conference on Complementary and Integrative MedicineIntegrative Medicine.

Troubling Combinations?

The study included women and men with osteoporosisosteoporosis enrolled in an ongoing Canadian bone- loss trial. At a five-year follow-up, the average age of the study participants was 70. Just over two-thirds of the participants were female.

Researchers collected detailed data on the prescription, over-the-counter, and herbal drugs taken by the participants. Potentially dangerous drug-herbal interactions were analyzed for people taking the heart drugs Lanoxin, Lasix, and Coumadin, as well as antipsychotic and depressiondepression drugs like Xanax, lithium, Nardil, and selective serotonin reuptake inhibitors (SSRI), such as Prozac and Paxil.

Analysis of these data revealed that just 1.3% of the study subjects were taking combinations of prescription drugs and herbal products that are considered potentially dangerous.

Of the 514 study participants taking a cardiovascular drug, just 13 (2.5%) were also using a contraindicated herbal medication. And only one of the 514 participants taking one of the other prescriptions drugs of concern was also taking an herbal medication identified as potentially dangerous.

Of the 10 interactions seen among people taking the heart drug Lanoxin, nine involved the herbal supplement senna, which is found primarily in over-the-counter laxatives. Only one person taking the blood thinner Coumadin was also taking a contraindicated herbal supplement (ginkgo biloba).

Awareness of Risks

Researcher Shelly Vik tells WebMD that she expected to see more potentially harmful drug-herbal supplement interactions among the patients in the study. Vik is a graduate student in epidemiology at the University of Calgary.

"We know that quite a few people are using all of these drugs, but it doesn't look like a lot of people are using the dangerous combinations," she says. "This may be due to increased awareness of the potential risks among consumers and their physicians."

Of all the currently available herbal medications, the popular antidepressant alternative St. John's wort has received the most attention from investigators concerned about drug interactions.

A 2003 study showed that the herb can reduce the effectiveness of as many as half of all prescription and over-the-counter drugs, including heart drugs, seizure drugs, depressiondepression and anxiety drugs, and even oral contraceptives.

In 2000, University of Texas Southwestern molecular biologist Stephen Kliewer, PhD, and colleagues concluded that St. John's wort does this by activating protein receptors in the liver known as CYP3A4, which regulate the oxidation of most drugs.

Kliewer tells WebMD that researchers began studying the herbal product after physicians started seeing evidence of interactions among their patients who were also on prescription drugs.

Surveys suggest that most patients still do not tell their doctors or pharmacist about the herbal supplements they take. Kliewer says it is critical that they do so to minimize the risk of interactions.

"People who take any dietary supplement should tell their doctor about it," he says. "These are medicines, and people should treat them as such."

Show Sources

SOURCES: Vik, S. Presentation, North American Research Conference on Complementary and Integrative Medicine, Edmonton, Alberta, Canada, May 24-27, 2006. David Hanley, MD, FRCPC, professor of medicine, division of endocrinology and metabolism, University of Calgary, Alberta, Canada. Stephen Kliewer, PhD, professor, department of molecular biology, University of Texas Southwestern Medical Center. U.S. Pharmacist web site: "Herbal Sales Reach Mainstream Market," WebMD Medical News: "Many Herbal Remedies May Interact with Popular Blood Thinner." WebMD Medical News: "St. John's Wort Affects Other Drugs."
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