Progesterone or progestin as menopausal ovarian hormone therapy: recent physiology-based clinical evidence

PURPOSE OF REVIEW: Provide evidence-based recent data on oral micronized progesterone (OMP) and progestins in menopausal hormonal therapy (MHT). RECENT FINDINGS: Medroxyprogesterone acetate (MPA) increases breast cancer acting through the glucocorticoid receptor; progestins in MHT increase thrombosis more than oral estrogens; MPA, but not OMP or other progestins, increase monocyte cell endothelium adhesion; MPA and estradiol (E2)/MPA have negative brain effects, whereas E2/progesterone (P4) has neuroregenerative brain effects. The 'window of opportunity' cardiovascular disease hypothesis is not supported by a randomized controlled trial showing that transdermal estradiol with sequential OMP in early menopause does not prevent increased carotid intimal media thickness; P4 in the cardiac electrical system opposes E2 effects and prevents sudden death/long QT syndrome; transdermal estradiol/OMP does not increase venous thromboembolism in observational data. P4 decreases breast cell proliferation and improves prognosis through P4 receptor alteration of estrogen receptor α genetic effects; OMP with conjugated equine estrogen (CEE)/estrogen (E)/E2 does not increase breast cancer in two prospective cohorts, one population-based. Endometrial cancer is increased in MHT of CEE/E/E2+cyclic OMP at 200 mg/day. SUMMARY: New data show CEE/E/E2+MPA/P mechanisms for negative breast cancer, venous thromboembolism, cardiovascular system, and brain effects. OMP/P4 counterbalances CEE/E/E2-related negative effects on breast cancer and long QT syndrome. OMP effectively treats vasomotor symptoms and sleep disturbances, and could safely be used alone for symptomatic menopause.