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St. John's wort is an herbal supplement used by some people mainly to relieve mild to moderate depression. Some individuals also use it for conditions such as anxiety, sleep problems, premenstrual syndrome (PMS) and menopausal symptoms. The active ingredients in St. John's wort come from a plant with yellow flowers that has been used for centuries to treat a variety of medical conditions.

The effectiveness of St. John's wort in treating various disorders remains unproven, although some studies appear to show a benefit in relieving symptoms of minor depression.

St. John's wort is available in tea, capsule and extract form. Because it is a dietary supplement, the U.S. Food and Drug Administration does not regulate this over-the-counter product. Formulations sold under the name St. John's wort may contain very different active ingredients in varying amounts.

St. John's wort may cause the body to break down other medications more quickly or slowly. For this reason, the supplement has the potential to create significant and negative interactions when used with other medications, particularly antidepressants. Individuals taking any medication should talk with their physician before taking any herbal supplements. People taking birth control pills or certain heart, cancer or other drugs also may be advised to avoid St. John's wort.

People who experience depression or any other mental illnesses are at serious risk of major health consequences, including suicide. Therefore, patients should contact a physician for an appropriate diagnosis and intervention rather than trying to treat themselves with St. John's wort.