Herb-Drug Interactions with Ginkgo Unlikely
By Darin Ingels, ND
Healthnotes Newswire (January 15, 2004)—Adults taking a standardized extract of ginkgo (Ginkgo biloba) at recommended amounts over a two-week time period are unlikely to experience adverse effects from drug-herb interactions, according to a new study in the Journal of Clinical Psychopharmacology (2003;23:576–81). The findings of this study are particularly important to those who take ginkgo along with over-the-counter or prescription medications.
The use of herbal medicines in the United States has risen significantly over the past decade. One study showed a 380% increase in the use of herbs from 1990 to 1997. Since herbs are classified as dietary supplements and are not regulated by the United States Food and Drug Administration, access to these products is unrestricted. This could be potentially problematic for some individuals taking concurrent medications. Although ginkgo may interact adversely with blood-thinning medications such as aspirin (Bufferin®, Ecotrin®), warfarin (Coumadin®), or heparin; and medications that lower blood sugar such as glipizide (Glucotrol®), metformin (Glucophage®), and glimepiride (Amaryl®); many other potential drug-herb interactions have not been investigated.
The liver produces a series of enzymes (called the cytochrome P450 system) that are responsible for the detoxification of medications, hormones, chemicals, and other substances so that they can be excreted through the bowels or kidneys. Some compounds may speed up or slow down these enzymes, altering the metabolic rate in the liver and potentially affecting how medications get utilized in the body. If the rate of drug metabolism speeds up, then the effect of the drug is likely to be reduced, and if the rate of metabolism slows down, then the effect and the toxicity of the drug are likely to be increased. The need to understand how drugs and herbs interact is important in reducing the risk of interfering with the intended action of the medication.
Twelve healthy adults between the ages of 22 and 40 years participated in a three-part study to evaluate the influence of ginkgo extract on liver metabolism. Two major biochemical pathways in the liver (CYP 2D6 and CYP 3A4) are responsible for metabolizing a majority of the medications that people take. In the first part of the study, participants received concurrently two medications that are metabolized through one of the two pathways (30 mg of dextromethorphan [Robitussin DM®] and 2 mg of alprazolam [Xanax®]). Several blood and urine samples were taken over the following 60 hours to evaluate how these drugs were metabolized.
One week after taking the medications, each participant received 120 mg twice a day of ginkgo extract (containing 24% ginkgo flavonol glycosides and 6% terpene lactones) for two weeks. After completing treatment with the ginkgo extract, the same procedure used in part one of the study was repeated, except that 120 mg of ginkgo was given at the same time as the other medications.
No significant difference in the rate of drug metabolism was observed in one pathway (CYP 2D6). A small decrease in metabolism in the other pathway (CYP 3A4) was observed in men after alprazolam treatment; however, the authors of the study suggest that this decrease is not likely to be clinically significant.
The authors point out that their study evaluated only the two most common pathways of liver detoxification, but was not completely inclusive of all detoxification pathways. It is still possible that ginkgo could adversely interact with some medications. It is important to tell your physician or pharmacist if you are taking ginkgo or other herbal extracts to ensure that known drug-herb interactions are avoided.
Darin Ingels, ND, MT (ASCP), received his bachelor’s degree from Purdue University and his Doctorate of Naturopathic Medicine from Bastyr University in Kenmore, WA. Dr. Ingels is the author of The Natural Pharmacist: Lowering Cholesterol (Prima, 1999) and Natural Treatments for High Cholesterol (Prima, 2000). He currently is in private practice at New England Family Health Associates located in Southport, CT, where he specializes in environmental medicine and allergies. Dr. Ingels is a regular contributor to Healthnotes and Healthnotes Newswire.
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