The Mayo Clinic is warning consumers about the serious and potentially deadly side effects they may face from taking over-the-counter herbal supplements. The warning was sent in the Clinic’s August 2009 issue of the Mayo Clinic Health Letter.

According to the Mayo Clinic warning, consumers may face serious health risks by taking herbal supplements, especially if they are taking other medications or are about to undergo surgery. In addition to increasing the risk of life-threatening problems such as liver or kidney damage, bleeding or an irregular heartbeat, herbal supplements can interact with other drugs a patient may be taking or alter the safety of surgical procedures.

The Mayo Clinic advised patients who are taking anti-clotting drugs, heart medications, anti-seizure drugs or immunosuppressants to speak with their doctor before taking over-the-counter herbal products due to the risk of side effects. Some of the supplements sited in the Mayo Clinic warning included St. John’s wort, garlic, ginseng, ginger and S-adenosylmethionine (SAM-e).

In addition to the risk of drug interactions or surgical complications, herbal supplements have also been linked to a number of other serious side effects. In 2004, the Food and Drug Administration banned all herbal products containing ephedra (ma huang)—including some ephedra-containing supplements that were marketed as “herbal Fen Phen” in the wake of the 1997 Fen Phen recall. At least 100 deaths were linked to the use of herbal Fen Phen or other ephedra products at the time the recall was issued.