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National Center for Complementary and Integrative Health

6 Tips: How Herbs Can Interact With Medicines

Many people take both herbal supplements and prescription or over-the-counter medicines. But did you know that these medicines and supplements may interact in harmful ways? Some supplements can decrease the effects of medicines, while others can increase their effects, including unwanted side effects. Unfortunately, for many medicines and supplements there’s currently little information on possible interactions, and more research is needed. But here are 6 things you should know about herbs that have a high risk of potential interactions with certain medications.

  1. St. John’s wort interacts with many types of drugs. In most instances, it speeds up the processes that change the drug into inactive substances, leading to a decrease in drug levels in your body. St. John’s wort can also interact with some drugs, including certain types of antidepressants, in a different way that increases the risk of serious serotonin-related side effects.

  2. There are uncertainties about whether Asian ginseng might interact with certain medicines, such as calcium channel blockers and other medicines used for high blood pressure, statin medicines used for high blood cholesterol, and some antidepressants. 

  3. Concentrated green tea supplements can reduce blood levels of some drugs, such as the cholesterol-lowering drug atorvastatin and the beta-blocker nadolol.

  4. The herb goldenseal may change the way your body processes many drugs, including the diabetes medicine metformin.

  5. People who take medicines with a narrow therapeutic index (digoxin, cyclosporine, warfarin, and others) should take special care to tell their health care providers about their use of herbal supplements. A narrow therapeutic index means that if the amount of the drug is even a little too low or too high, it can cause big problems. 

  6. When you visit your health care providers, it’s important to tell them about all the medicines and supplements you take. Bring a written list of everything you take, how often you take each product, and the doses.