Estradiol is a form of estrogen. Estrogen is a female sex hormone that is involved in the development and maintenance of the female reproductive system. Norethindrone is a form of progesterone. Progesterone is a female hormone important for the regulation of ovulation and menstruation. Together, estradiol and norethindrone are used to treat the symptoms of menopause, and to replace estrogen in conditions such as hypogonadism, removal of the ovaries, or primary ovarian failure that result in a lack of estrogen. Estradiol and norethindrone are also used to prevent thinning of the bones (osteoporosis).