Progestogens mediate their contraceptive effects in women both by inhibiting ovulation (via their antigonadotropic effects) and by thickening cervical mucus, thereby preventing the possibility of fertilization of the ovum by sperm. Progestogens have functional antiestrogenic effects in various tissues like the endometrium via activation of the PR, and this underlies their use in menopausal hormone therapy (to prevent unopposed estrogen-induced endometrial hyperplasia and endometrial cancer). The PRs are induced in the breasts by estrogens, and for this reason, it is assumed that progestogens cannot mediate breast changes in the absence of estrogens. The off-target activities of progestogens can contribute both to their beneficial effects and to their adverse effects.