It's a phytoestrogen , a plant with estrogenic properties. Black cohosh, sold as Remifemin, is touted as a natural alternative for female problems. It's widely used in Germany to control hot flashes and menstrual cramps. While it may help, the evidence on safety and efficacy is limited, based largely on small, poorly controlled studies. Nausea is the most common side effect, but very high doses can lead to vomiting, headaches, dizziness, low blood pressure, pain in the arms and legs, or heavy uterine bleeding.
Side effects are more common when the dried or powdered form of the root is used.
The German E Commission, which is similar to our Food and Drug Administration, limits the use of black cohosh to six months because there are no long-term studies available. There are a number of other ways to control hot flashes. Start by avoiding triggers such as alcohol, spicy food, caffeine or hot climates. Decrease the stress in your life, or at least learn to handle it better. Practice relaxation techniques like deep breathing or regular exercise .