The reddish substance in the plant’s flowers contains numerous biologically active compounds, including hypericin and hyperforin. (See also Overview of Dietary Supplements.)
People take St. John’s wort mostly to relieve symptoms of depression. Study results vary, but there may be a benefit in treating mild to moderate short-term depression. Overall, some studies show St. John’s wort may benefit people with mild to moderate depression and may be as effective as some traditional antidepressants. However, St. John's wort is not effective for major depression.
St. John’s wort has been used in the treatment of skin disorders, including psoriasis, and attention-deficit/hyperactivity disorder (ADHD) in children, but its effectiveness in treating these disorders is unproved.
St. John’s wort may cause increased sensitivity to sunlight. Other side effects include dry mouth, digestive tract symptoms, fatigue, confusion, and mania (in people with bipolar disorder).
Pregnant women should not take this supplement because it increases muscle tone in the uterus and thus may increase the risk of a miscarriage.
One of the larger problems with St. John’s wort is that it may interact negatively with a number of drugs people take (see table Drug Interactions With St. John's Wort). These interactions may lead to toxic reactions or ineffectiveness of the drug.
Drug Interactions With St. John's Wort
The following is an English-language resource that may be useful. Please note that THE MANUAL is not responsible for the content of this resource.
National Institutes of Health (NIH), National Center for Complementary and Integrative Health: General information on the use of St. John’s wort as a dietary supplement