Q. Last months column detailed potential interactions between vitamins and systemic medications or conditions. Can other supplements pose a risk?

A. There are many over the counter supplements your patients may be using to self-treat a variety of conditions. While some have beneficial effects, others could pose a risk, especially when taken with prescription medications. Cases of herb-drug interactions are well-documents in medical literature.

Approximately one quarter of adults in the United States use herbs to treat medical illnesses.¹

The Lower Mississippi Delta Nutrition Intervention Research Initiative estimates adverse food-drug interactions may be the fourth leading cause of death in hospitalized patients.²

While most herbal medicines are safe, they are subject to only limited regulations and oversight.¹ Communication with your patients is key to prevent adverse reactions.

A team of Italian researchers conducted an extensive literature review to examine possible side effects of the seven top-selling herbal medicines: ginkgo biloba, St. Johns wort, ginseng, garlic, echinacea, saw palmetto and kava.³ No interactions were seen with echinacea or saw palmetto, but some were observed with the other five.³

St. Johns wort (Hypericum perforatum). This herb is effective and safe when used alone to treat mild-to-moderate depression.⁴ However, the National Center for Complimentary and Alternative Medicine at the National Institutes of Health warns that St. Johns wort affects the activity of liver enzymes, which may affect how the body processes other medications.

Ginkgo biloba. This herb may be an alternative to hormone therapy for postmenopausal women and may increase memory retention.⁵ A study of 27 patients with bilateral normal tension glaucoma found ginkgo biloba may improve preexisting visual field damage.⁶

However, ginkgo biloba can also cause bleeding when combined with warfarin (Coumadin, Bristol-Myers Squibb).³ This is likely due to the herbs platelet-inhibiting properties.

Ginseng (Panax ginseng). The main active components in ginseng, ginsenosides, have anti-inflammatory, antioxidant and anti-cancer mechanisms.⁷ Ginseng may also improve psychological and immune functions and conditions associated with diabetes.⁷ Even so, caution patients about using ginseng with hypogylcemic agents or insulin.⁷

Garlic (Allium sativum). Often recommended for heart health, garlic can decrease blood levels of warfarin. When taken with chlorpropamide, a glucose-lowering agent, it may also cause hypogylcemia.³

Kava (Piper methysticum). Clinical studies have shown that kava is effective in treating anxiety.⁸ However, kava can cause a semi-comatose state when taken with alprazolam, an anti-anxiety agent.³ Recently, anecdotal reports of hepatic toxicity from kava lactones have surfaced, but most incidences were reversible with cessation.⁹  

As more medications enter the market, new indications will likely develop. It behooves us to learn more about nutrition and drug interactions, says Robert Abel, M.D., of Willington, Del. Its also important to keep up with new studies about this class of treatment.

1. Bent S, Ko R. Commonly used herbal medicines in the United States: a review. Am J Med. 2004 Apr 1;116(7):478-85.
2. McCabe BJ. Prevention of food-drug interactions with special emphasis on older adults. Cur Opin Clin Nutr Metab Care. 2004 Jan;7(1):21-6.
3. Izzo AA, Ernst E. Interactions between herbal medicines and prescribed drugs: a systematic review. Drugs. 2001;61(15):2163-75.
4. Izzo AA. Drug interactions with St. Johns Wort (Hypericum perforatum): a review of the clinical evidence. Int J Clin Pharacom Ther. 2004 Mar;42(3):139-48.
5. Oh SM, Chung KH. Estrogenic activities of Ginko biloba extracts. Life Sci. 2004 Jan 30;74(11):1325-35.
6. Quaranta L, Bettelli S, Uva MG, et al. Effect of Ginko biloba extract on preexisiting visual field damage in normal tension glaucoma. Ophthalmology. 2003 Feb;110(2):359-62.
7. Kiefer D, Pantuso T. Panax ginseng. Am Fam Physician. 2003 Oct 15;68(8):1539-42.
8. Singh YN, Singh NN. Therapeutic potential of kava in the treatment of anxiety disorders. CNS Drugs. 2002;16(11):731-43.
9. Clough AR, Bailie RS, Currie B. Liver function test abnormalities in users of aqueous kava extracts. J Toxicol Clin Toxicol. 2003;41(6):821-9.