What Physicians Should Know about Herbal Medicines.
Potential Herb-Drug Interactions in Older People
Julie Dergal, MSc
Kunin-Lunenfeld Applied Research Unit,
Baycrest Centre for Geriatric Care,
Toronto, ON.
Paula A. Rochon, MD, MPH, FRCPC
Baycrest Centre for Geriatric Care,
Assistant Professor of Medicine,
University of Toronto, Toronto, ON.
Introduction
The use of herbal medicines has recently gained a great deal of acceptance in North America. In 1996 in the United States, an estimated two billion dollars was spent on herbs, tablets, extracts, capsules, and teas, in health food stores.1 In 1997, Eisenberg conducted a telephone survey of 2055 people and found that 12% used herbal medicines, a 4-fold increase from 1991.2 Despite the widespread use of herbal medicines in North America, little research has examined the safety of these alternative medicines, particularly when taken in conjunction with conventional medicines. A common misconception about alternative medicines is that they are "natural" and are, therefore, safe. However, herbal medicines are marketed as dietary supplements and, as such, are not subject to the rigorous standards established for conventional drug therapies. This means that the quality and content of herbal medicines are largely unregulated and uncontrolled.
Traditionally, the people most likely to use herbal medicines are those for whom conventional medicine offers little hope, such as people with dementia. Many herbal medicines target symptoms commonly experienced by older people with dementia including memory loss, depression and insomnia. Coleman et al.3 interviewed 101 caregivers of dementia patients and found that more than half of the patients had tried at least one alternative medicine. Similarly, Hogan et al.4 conducted a telephone interview of 115 caregivers of older adults with cognitive impairment attending a memory clinic. Close to 40% used some form of alternative medicine. While many older people with dementia may be users of herbal medicines, they are probably already taking multiple conventional drug therapies. Therefore, older people with dementia are a vulnerable population and are at risk for experiencing an interaction between herbal and conventional medicines potentially leading to an adverse event.
There have been numerous reports in the medical literature of interactions between herbal and conventional medicines. Herbal medicines taken in addition to conventional medicines, may cause interactions that lead to problems such as increased bleeding, increased sedation or coma. Gold et al.5 conducted a systematic review to identify potential herb-drug interactions reported in the literature. They identified the following herbal medicines as those most commonly used for cognitive symptoms of dementia--memory loss and decreased concentration--and related psychiatric symptoms--anxiety, depression and insomnia: ginkgo biloba, marketed as a "memory enhancer;" ginseng, a so-called "energy booster;" kava and valerian, intended to work as sedatives; and St. John's Wort, commonly used to treat depression. We will summarize the findings of this systematic review identifying herb-drug interactions, and discuss the implications for clinical practice.
Ginkgo Biloba
Ginkgo biloba is commonly used as a remedy for memory loss. Four separate articles have described interactions between ginkgo biloba and conventional medications. Ginkgo biloba extract is an inhibitor of platelet-activating factor. Long-term use has been linked to an increased bleeding time, subdural hematomas and spontaneous hemorrhage. Ginkgo may also augment the effects of anticoagulants. Gold et al. suggest that short term use of ginkgo biloba may have antiplatelet effects, with a possibility for increased risk if acetylsalicylic acid or other platelet aggregation inhibitors are being used concurrently. There is also a potential interaction between ginkgo biloba and trazodone.
Ginseng
Ginseng is commonly used to improve concentration, making it appealing to patients with dementia. Gold et al. reviewed seven articles that describe interactions between ginseng and conventional medications. Ginseng may interact with