Drug & Herbal Medicine Interactions

Use of herbal remedies has been increasing in the United States. As of 1994, it is legal to sell herbs as dietary supplements as long as the manufacturer makes no therapeutic claim. However, there are no standards for potency or purity of herbs sold in the U.S., unlike some other countries. As a result, U.S. formulations can vary widely in quality, and in content of active ingredients.

Some herbs have already established a history of severe, even fatal, reactions in people. Because of this, the government has issued warnings on the use of ephedra (ma huang), chaparral, comfrey, pennyroyal, assafras, germanium, guargum, jim bu huan, willow bark and yohimbe.

The following table lists herbs that have potential for, or have been documented as having, interactions with prescription medicines:

Drug/category	Herb(s)	Resulting interaction
Coumadin, aspirin, Vitamin E, anti-coagulants	bilberry, bromelain, ginger, gingko biloba, melilot, pau d'arco, tonka beans, woodruff	prolonged clotting time
Dilantin, Phenobarbitol	chaparral, comfrey	liver damage
Hypertension medications	Licorice	elevation of blood pressure, loss of potassium
Immunosuppressive medication	astragalus, echinacea, maitake, reishi, Siberian American ginseng	enhanced immune response
Lanoxin	dogbane, foxglove, lily-of-the-valley, oleander	digitalis toxicity
Lasix, HCTZ, other diuretics	Dandelion	serious dehydration, loss of potassium
Laxatives	ginseng	loss of potassium
Valium, alcohol, other sedatives	kava kava, passion flower, St. John's Wort, Valerian	elevation of blood pressure, serotonin syndrome