Testosterone is aromatized into estradiol, and norethisterone, the 19-nortestosterone analogue of ethisterone, has similarly been shown to be aromatized into ethinylestradiol. In accordance, high doses of norethisterone have been found to be associated with marked increases in urinary estrogen excretion (due to metabolism into ethinylestradiol), as well as with high rates of estrogenic side effects such as breast enlargement in women and gynecomastia in men and improvement of menopausal symptoms in postmenopausal women. In contrast, ethisterone and other progestogens such as progesterone and hydroxyprogesterone caproate do not increase estrogen excretion and are not associated with estrogenic effects, indicating that they have little or no estrogenic activity. Similarly, although ethisterone showed estrogenic effects in the uterus and vagina in rats, few or no such effects were observed in women treated with the medication, even at very high doses. As such, ethisterone does not appear to share the estrogenic activity of norethisterone, at least in humans. Aside from ethinylestradiol, 17α-ethynyl-3α-androstanediol and 17α-ethynyl-3β-androstanediol may be estrogenic metabolites of ethisterone.