St. John’s wort is most commonly used for depression and conditions that sometimes go along with depression such as anxiety, tiredness, loss of appetite and trouble sleeping. There is some strong scientific evidence that it is effective for mild to moderate depression.

Other uses include heart palpitations, moodiness and other symptoms of menopause, mental disorders that present physical symptoms, premenstrual syndrome (PMS), attention deficit-hyperactivity disorder (ADHD), obsessive-compulsive disorder (OCD), social phobia, and seasonal affective disorder (SAD).

St. John’s wort has been tried to help quit smoking, for fibromyalgia, chronic fatigue syndrome (CFS), burning feelings in the mouth, migraine and other types of headaches, muscle pain, nerve pain and nerve damage throughout the body, pain that travels down the sciatic nerve in the leg, and irritable bowel syndrome. It is also used for cancer (including brain cancer), HIV/AIDS, hepatitis C, herpes simplex, to help with a procedure to unblock clogged arteries, weight loss, and to treat a disease that causes the skin to lose color.

St. John’s wort might cause serious interactions with some drugs. Because of this, many counties have banned the use of it without the doctor presciption.