Besides the natural progestin, progesterone, there are different classes of progestins, such as retroprogesterone (i.e. dydrogesterone), progesterone derivatives (i.e. medrogestone) 17alpha-hydroxyprogesterone derivatives (i.e. chlormadinone acetate, cyproterone acetate, medroxyprogesterone acetate, megestrol acetate), 19-norprogesterone derivatives (i.e. nomegestrol, promegestone, trimegestone, nesterone), 19-nortestosterone derivatives norethisterone (NET), lynestrenol, levonorgestrel, desogestrel, gestodene, norgestimate, dienogest) and spironolactone derivatives (i.e. drospirenone). Some of the synthetic progestins are prodrugs, which need to be metabolized to become active compounds. Besides the progestogenic effect, which is in common for all progestins, there is a wide range of biological effects, which are different for the various progestins and have to be taken into account, when medical treatment is considered.