Black cohosh was first used for medicinal purposes by Native American Indians. It became a popular treatment for women's health issues in Europe in the mid-1950s. Since then, black cohosh has been used to help relieve symptoms of menopause, premenstrual syndrome (PMS), painful menstruation, acne, weakened bones (osteoporosis), and for starting labor in pregnant women.
The root of black cohosh contains several chemicals that might have effects in the body. Some of these chemicals work on the immune system and might affect the body's defenses against diseases. Some might help the body to reduce inflammation. Other chemicals in black cohosh root are thought to work similar to serotonin, which is a chemical that helps the brain send messages to other parts of the body.
In some parts of the body, black cohosh might increase the effects of estrogen. In other parts of the body, black cohosh might decrease the effects of estrogen. However, black cohosh should not be thought of as an "herbal estrogen" or a substitute for estrogen. It is more accurate to think of it as an herb that somewhat mimics estrogen in some people.
Taken over a two month period, two caps twice a day has been shown in some people to decrease menopausal symptoms such as hot flashes and sweats.