Progestogens in hormonal replacement therapy: new molecules, risks, and benefits.

While the benefits of progestogen use in hormone replacement therapy (HRT) are well recognized as far as endometrial protection is concerned, their risks and drawbacks have generated controversial articles. Several risks are attributed to progestogens as a class-effect; however, the progestogens used in HRT have varying pharmacological properties and do not induce the same side effects. Natural progesterone (P) and some of its derivatives, such as the 19-norprogesterones (Nestorone, nomegestrol acetate, trimegestone), do not bind to the androgen receptor and, hence, do not exert androgenic side effects. Newly synthesized molecules such as drospirenone or dienogest have no androgenic effect but do have a partial antiandrogenic effect. Drospirenone derives from spironolactone and binds to the mineralocorticoid receptor. When the cardiovascular risk factors are considered, some molecules with a higher androgenic potency than others attenuate the beneficial effects of estrogens on the lipid profile as well as the vasomotion. On the other hand, other progestogens devoid of androgenic properties do not exert these deleterious effects. The epidemiological data do not suggest any negative effect of the progestogens administered together with estrogens on cardiovascular morbidity or mortality. However, recent results suggest that in women with established coronary heart disease, HRT may not protect against further heart attacks when the progestogen selected possesses androgenic properties. The data related to the progestogen effect on breast tissue has been interpreted differently from country to country. However, it has been admitted that, according to the type of progestogen used and the dose and duration of its application, a predominant antiproliferative effect is observed in the human breast cells. As far as breast cancer risk is concerned, most epidemiological studies do not suggest any significant difference between the estrogens given alone or combined with progestogens in HRT. Complying with the classic contraindications of HRT and selecting molecules devoid of estrogenic, androgenic, or glucocorticoid effect should allow a larger use of the progestins without any major drawback.