While most herbal treatments are relatively safe, some can have negative side-effects. In addition, the combination of certain herbs with select synthetic medications can potentially cause a severe reaction. Izzo and Ernst completed a search of the literature to determine possible interactions with the seven top-selling herbals (St. John’s wort, ginkgo, ginseng, garlic, echinacea, saw palmetto, and kava) and prescribed drugs.
All human data relating to herb-drug interactions were used, regardless of whether they were based on individual case reports, clinical trials, etc. Please see the article referenced below for a comprehensive listing. They report that St. John’s wort can react with some oral contraceptives, Imodium, or serotonin-reuptake inhibitors.
Ginkgo can interact with a specific anticoagulant, a type of diuretic, and a specific antidepressant.
Ginseng lowers blood concentrations of an anticoagulant and may induce mania if used with a specific antidepressant.
Garlic interacts with an anticoagulant and a drug for diabetes.
Kava, in combination with an anti-anxiety drug or one commonly taken for Parkinson’s, can cause serious problems.
Echinacea and saw palmetto had no interactions noted.
Though some reactions may be rare and may have involved unusually large doses of either the herbs or drugs, the assumption that herbs are harmless because they are natural is a misconception. And, when a natural herb is taken along with a man-made drug, care is required. Physicians should be aware of potential interactions and should question patients before prescribing drugs. And, patients should not start herbal medicines without checking with their prescribing physician. (Unfortunately, physicians are not always aware of herb-drug interactions.)
Izzo AA, Ernst E. Interactions between herbal medicines and prescribed drugs: a systematic review. Drugs 2001, 61(15):2163-75.