Herb and Drug Interactions: An Emerging Issue

| December/January 2000

  • If you ask for Siberian ginseng by name in a Chinese herb shop, you’re likely to be met with bewilderment. Eleutherococcus senticosus is more properly called eleuthero, since botanically, it’s not a gingseng.
  • Licorice should be used with caution by those taking prescription diuretics and some heart medications.
  • Some studies suggest that St. John’s wort may interfere with a function of the digestive system, raising or lowering the levels of some drugs in the bloodstream.
  • American skullcap has long been traditionally used as a gentle sedative. Now researchers have discovered it contains two of the same sedative compounds as its better-researched Chinese relative, Baikal skullcap.

In 2000, the possibility that herbs may interact with prescription drugs caught worldwide attention, despite the fact that such herb-drug interactions are rare. Concern about these interactions increased after wide coverage of two research letters published in the February 12, 2000 issue of The Lancet.

Focus on this issue occurred largely in professional medical literature, as more health-care practitioners prescribe herbs or discuss the use of herbs with their patients. Various surveys have revealed that many consumers who are taking herbs fail to tell their physician or healthcare provider. About 24 percent (more than 44 million) of American consumers use herbs routinely, according to a survey published by Prevention magazine. And 18.4 percent of those surveyed were taking both prescription medications and herbal dietary supplements or multivitamins.

But experts in medicinal herbs caution that herb-drug interactions shouldn’t be taken out of context. Historically, herbs have caused relatively fewer side effects than prescription drugs. For example, clinical trials show that the herb saw palmetto (Serenoa repens) causes fewer problems than conventional prescription drugs for the treatment of benign prostatic hyperplasia. And the German Commission E Monographs, more than 300 therapeutic monographs produced over a sixteen-year period, record only thirty-five potential drug interactions.

Certain herb-drug interactions are well-documented and worth watching for. Below, we summarize some of the recent research. Talk to your physician if combining any of these herbs and pharmaceutical drugs.

St. John’s wort. One report suggested that the use of St. John’s wort (Hypericum perforatum)in AIDS patients taking the protease inhibitor drug indinavir led to lower blood levels of the drug. The authors suggested that St. John’s wort may interfere with a function of the digestive system—called the cytochrome P450 enzyme system —which may in turn produce lower or higher levels of the drugs in the bloodstream. A second letter to the editor in The Lancet attributed a possible drug interaction with cyclosporine in two cases of acute transplant rejection of heart transplant patients to use of the drugs and St. John’s wort. Less publicized scientific reports had previously warned that using St. John’s wort with prescription drugs such as digoxin, theophylline, and other drugs may also produce interactions.

But St. John’s wort is only one of many plant products that may interact with the cytochrome P450 enzyme system. Others include grapefruit juice, broccoli, cabbage, Brussels sprouts, red wine, and tobacco.

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