Evening primrose oil and black cohosh are two herbal supplements that are often used together to combat menopausal concerns, such as hot flashes and mood swings. Evening primrose oil is derived from the seeds of the evening primrose plant, which is native to North America. It has been used for centuries by indigenous peoples to treat a variety of issues. Black cohosh, on the other hand, is a plant native to North America and has been used for centuries by Native Americans to treat a range of conditions, including menopausal concerns. The combination of these two supplements is thought to synergistically promote balance of hormone levels in the body for both men and women.