St. John's wort is a plant with yellow, star-shaped flowers and five petals that grows in Europe, North and South America, Australia, New Zealand, and Eastern Asia. The plant grows in sunny, well-drained areas. It grows to be 50-100 cm tall.
 St. John's wort might cause serious interactions with some medications. Because of this, France has banned the use of St. John's wort in products. In other countries St. John's wort is only available with a prescription.
 St. John's wort is most commonly used for "the blues" or depression and symptoms that sometimes go along with mood such as nervousness, tiredness, poor appetite, and trouble sleeping. There is some strong scientific evidence that it is effective for mild to moderate depression.
 St. John's wort is also used for symptoms of menopause such as hot flashes and mood changes.

An oil can be made from St. John's wort. Some people apply this oil to their skin to treat wounds. Applying St. John's wort directly to the skin is risky. It can cause serious sensitivity to sunlight.

 How does it work? For a long time, scientists thought a chemical in St. John's wort called hypericin was responsible for its effects on improving mood. More recent information suggests other chemicals like hyperforin may play a larger role. These chemicals act on messengers in the nervous system that regulate mood. Taking St. John's wort extracts by mouth improves mood and decreases nervousness and tiredness related to depression. It seems to be about as effective as many prescription drugs. The American College of Physicians-American Society of Internal Medicine guidelines suggest that St. John's wort can be considered an option along with prescription medications for short-term treatment of mild depression. However, since St. John's wort causes many drug interactions, the guidelines suggest it might not be a good choice for many people. St. John's wort might not be as effective for more severe cases of depression. Most research shows that taking St. John's wort by mouth can help reduce hot flashes and other symptoms of menopause. Some evidence suggests that specific combinations of St. John's wort plus black cohosh (Remifemin; Remifemin Plus; Gynoplus) can also improve some symptoms of menopause such as hot flashes and mood changes. But not all St. John's wort combination products seem to be beneficial.