As herbal remedies grow in popularity it becomes increasingly important that users and their health care practitioners know of the potential interactions between herbs and pharmaceutical drugs. Many herbs have powerful effects which may be increased or counteracted by pharmaceutical drugs and vice versa. Dr. Lucinda Miller, a pharmacist at the Texas Tech University, has published a comprehensive report listing the most common interactions. Among her main findings are the following:

• Echinacea, if used for more than eight consecutive weeks, could cause liver toxicity and therefore should not be used with drugs such as anabolic steroids, amiodarone, and methotrexate which are toxic to the liver.
• NSAIDs (nonsteroidal anti-inflammatory drugs) should not be used when feverfew is taken for migraine headaches.
• Feverfew, garlic, ginger, ginseng, and Ginkgo biloba all affect bleeding time and should not be taken by patients using warfarin.
• Until more data is available, St. John's wort should not be taken with monoamine oxidase inhibitors or selective serotonin reuptake inhibitors like Prozac and Paxil.
• Licorice, plantain, hawthorn, and ginseng may interfere with digoxin therapy and valarian root should not be taken when barbiturates are used.
• Evening primrose oil and borage are contraindicated in patients taking anticonvulsants and licorice can offset the pharmacological effect of the potassium-sparing diuretic spironolactone.
• Immunostimulants such as Echinacea and zinc should not be given with immunosuppressants such as corticosteroids (prednisone, etc.) and cyclosporine and are contraindicated in patients suffering from rheumatoid arthritis and systemic lupus erythematosus.

Dr. Miller points out that more than 60 million Americans now use herbal remedies, but that 70 per cent of them do not tell their physician or pharmacist that they do so. She recommends that physicians when taking a patient's medical history pay just as much attention to what herbs they are taking as to what drugs they are taking. (171 references)
Miller, Lucinda G. Herbal medicinals. Archives of Internal Medicine, Vol. 158, November 9, 1998, pp. 2200-11