Based on "in vitro" research, ethisterone and norethisterone are about equipotent in their values for activation of the androgen receptor (AR), whereas, conversely, norethisterone shows markedly increased potency relative to ethisterone in terms of its EC50 for the progesterone receptor. As such, there is a considerable separation in the ratios of androgenic and progestogenic activity for ethisterone and norethisterone. Moreover, at the larger dosages in which it is used to achieve equivalent progestogenic effect, ethisterone has more androgenic effect relative to norethisterone and other 19-nortestosterone progestins. However, the androgenic activity of ethisterone has in any case been described as weak. Due to its androgenic activity, ethisterone has been associated with the masculinization of female fetuses in women who have taken it during pregnancy. The 5α-reduced metabolite of ethisterone, 5α-dihydroethisterone, has been found to show reduced androgenic activity relative to ethisterone. Interestingly, ethisterone showed antiandrogenic activity when co-administered with dihydrotestosterone (DHT) in animals, whereas 5α-dihydroethisterone did not.