Progestogens are all steroid compounds with progestogenic activity of different intensity regarding progestogenic action per molecule. Some of the compounds used therapeutically act as prodrugs, which need to be metabolized in the body before the respective function is obtained (see Table 2.1). Progestogens not only have different structures, but each progestogen expresses a different pattern of partial effects. This partial effect pattern is responsible for the different clinical effects and side effects seen for each progestogen.

Progesterone and all the other synthetic progestogens are called progestogens. If progesterone is excluded the term “progestin” is used. An overview of the various types of progestogens is shown in Table 2.2 [3, 4]. The development of the classification of the progestogens started in the 1950s. Removal of the C19-Methyl-group increased progestogenic activity and oral resorption but decreased androgenic action. The introduction of a 17α-Ethyl-group produced ethisterone, which had a much higher binding affinity to the progesterone receptor. Both processes together produced the progestogen norethisterone (norethindrone in the United States), which is highly active, well tolerated and has been clinically available since 1957 [5]. In 1951 Norethisterone acetate (NETA) was synthesized by Schering and Norethinodrel by Searle. In the 1960s, the prodrugs norethisterone (NET), lynestrenol, ethinylethinodiol acetate, norethinodrel and dl-norgestrel appeared on the market. The first progesterone derivative 17-acetoxyprogesterone was developed by Schering in 1954 followed by medroxyprogesterone acetate in 1957. This was followed by medrogestone acetate and chlormadinone acetate in 1959. The retroprogesterone dydrogesterone was formed from progesterone by UV light exposure [6]. Dydrogesterone is still the only retroprogesterone presently available on the market. In 1961 cyproterone acetate became clinically available, followed by desogestrel in 1972 (Organon). Thereafter gestodene, dienogest and the spirolactone derivative drospirenone followed [7].