 Effects of estrogen deficiency in women are climacteric symptoms and bone loss, which can efficiently be treated by substituting with estrogens 1. Unopposed estrogen treatment, however, increases the risk for endometrial hyperplasia and subsequent carcinoma. For example in the HOPE study Womens Health, Osteoporosis, Progestin, Estrogen study 2, 3, after two years of treatment with conjugated equine estrogens 0.625mgday CEE the rate of hyperplasia went up to 27,7. When the treatment was combined with MPA 2.5 mg the incidence of hyperplasia completely disappeared. Thus, the addition of progestagens is necessary for endometrial safety. Progestagen addition in continuous combined estrogen plus progestin therapy, however, also causes negative side effects like withdrawal bleeding and an increased breast cancer incidence that was recently documented in the Womens Health Initiative 4 and Million Women Study 5. 