According to WebMD, St. John's wort is an herb that is commonly used to treat depression and by-products of depression, including anxiety, fatigue, loss of appetite and insomnia. Scientific evidence supports the claim that St. John's wort is effective in treating mild to moderate depression. It is also sometimes used to treat heart palpitations, moodiness, attention deficit-hyperactivity disorder, obsessive-compulsive disorder and seasonal affective disorder.
WebMD further states that St. John's wort can be made into an oil to treat skin-related problems, such as bruises and scrapes, muscle pain and inflammation. Applying St. John's wort directly to the skin, however, is not recommended due to its photosensitive properties. It is believed that St. John's wort is effective in treating some cases of depression due to the presence of the chemicals hypericin and hyperforin. WebMD mentions that the use of St. John's wort is banned in France because of concerns that the herbal supplement can interact negatively with certain medications. Japan, the United Kingdom and Canada include warnings on products that contain St. John's wort.
St. John's wort, although native to Europe, is commonly found growing in North America, according to WebMD. It is also grown as a crop in Australia, which contributes around 20 percent of the world's supply. The medicinal uses of St. John's wort go back to ancient Greece. The name of the herb refers to John the Baptist, as the plant blooms around the day of his birth.