Chemical. CAS 65928-58-7. Formula C20H25NO2. MW 311.42. Synthetic. Dienogest is an agonist of the progesterone receptor PR. It is an orally active synthetic progestogen with approximately 10% of the relative affinity of progesterone. However it shows very potent progestagenic effects in the endometrium with some antiandrogenic activity and without any androgenic, glucocorticoid or mineralocorticoid effects. It has been used alone or in combination as a contraceptive and to treat uterine fibroids. Dienogest inhibits ovulation primarily through peripheral action rather than by central action on gonadotrophin secretion. Unlike other progestogens, except in the case of its strong effects in the uterus, dienogest is said to lack antiestrogenic effects, and does not antagonize the beneficial effects of estradiol, for instance in the metabolic and vascular systems.