Dienogest (DNG) is a 19-nortestosterone derivative (a C-19 progestogen) with a cyanomethyl instead of an ethinyl group at the C-17 position, which may make the compound elicit fewer hepatic effects than other C-19 nortestosterone derivatives. Its similarity to norethisterone is reflected in its high endometrial efficacy, which could explain the high stability of the menstrual cycle women achieve when they use DNG in combination with ethinyl estradiol (EE) or with estradiol valerate (E2V). Its strong endometrial efficacy underlies the use of DNG (on its own) to treat endometriosis, and gives it antiproliferative and anti-inflammatory effects in the treatment of endometriotic lesions. Properties derived from its C-19 derivative structure include its short plasma half-life, of about 10h (which means the drug is not accumulated), and its high oral bioavailability, of more than 90%. However, DNG also has some of the properties of typical of progesterone derivatives, including a lack of effect on the metabolic and cardiovascular systems, and considerable antiandrogenic activity, the latter increased by its lack of affinity to the sex-hormone binding globulin (SHBG), in contrast to other C-19 progestogens. DNG has no glucocorticoid and no antimineralocorticoid activity. It also has no antiestrogenic activity, which suggests that it should not antagonize estradiol's beneficial effects. This is important for its use in the treatment of endometriosis, because, due to DNG's low gonadotropic activity, E2 levels are not decreased to zero, in contrast to treatments with gonadotropin-releasing hormone (GnRH) analogues. This maintenance beneficial E2 effects is of particular importance for the general tolerability of the first contraceptive pill to use E2V instead of EE, although clinical endpoint studies are still ongoing. These studies are expected, on the basis of its pharmacology, to demonstrate the cardiovascular safety of the new pill.