In terms of metabolism, ethisterone is not converted into pregnanediol in humans. This indicates that it is not metabolized into progesterone. No aromatization of ethisterone has been detected "in vivo", and no estrogenic metabolites were observed "in vitro" upon incubation of ethisterone in placental homogenates. This suggests that ethisterone may not be transformed into ethinylestradiol (17α-ethynylestradiol). 5α-Dihydroethisterone (5α-dihydro-17α-ethynyltestosterone), formed by 5α-reductase, is an active metabolite of ethisterone. 17α-Ethynyl-3α-androstanediol and 17α-ethynyl-3β-androstanediol, also formed via 5α-reductase, as well as other enzymes, are also potential metabolites of ethisterone.