Studies show that a dose of 20 to 40 milligrams of black cohosh twice daily is beneficial for treatment of menopausal symptoms, according to WebMD. Experts advise against taking it for longer than six months at a time, and doses of the supplement greater than 900 milligrams daily cause toxicity.
Black cohosh is useful in controlling menopausal symptoms, including hot flashes, headaches and mood changes, notes WebMD. Other symptoms it treats include sleep problems, night sweats, vaginal dryness and heart palpitations. A consultation with a doctor is the easiest way to determine the correct dosage of black cohosh and to determine if the supplement is safe for use with any existing medications.