Progesterone - Its Uses and Effects
Frederick R. Jelovsek MD
Progesterone is naturally secreted by the ovary in the second two weeks of the menstrual cycle in reproductive age ovulating women. Progesterone or progesterone-like substances called progestogens or progestins are also ingested by women in birth control pills, menopausal hormone replacement therapy, or just sometimes to induce a menstrual period or regulate abnormal bleeding problems if menses are skipping or bleeding is irregular or prolonged. Progesterone has been used also as therapy for PMS syndrome and for women with infertility or frequent pregnancy loss.
Many magazine articles have described the benefits and hazards of estrogens in women, but progesterone effects are much less known. A recent symposium, Fraser IS, Lobo R (eds and cochairs):Update on progestogen therapy. J Reprod Med 1999;44:139-232. brought together much of the current knowledge about progesterone administration for different purposes and helps answer some questions that many women may be interested in.
What is the difference between progesterone and progestogens (synthetic progesterones)?
Progesterone has the identical chemical structure to the substance made in a woman\'s body by the ovarian corpus luteum (gland formed after an egg is ovulated each month). Actually the progesterone is now synthetically made but it behaves as best we know, just like the body\'s natural progesterone once it is absorbed into the blood stream. This is to be distinguished from synthetic progesterone-like chemicals called progestogens which bind to the body\'s progesterone receptors and function for the most part, just like progesterone. Because they are chemically different than natural progesterone, they sometimes have side effects or actions that are different than progesterone.
Progestogens were originally developed because they were capable of being absorbed into the blood when ingested in pill form, whereas progesterone itself was not orally absorbed. Recently, however, it has been found that micronization of progesterone (making very tiny crystals of the progesterone) enhances absorption from the gastrointestinal tract. Thus micronized progesterone is now sometimes being used for menopausal hormone replacement therapy instead of progestogens. Birth control pills still have progestogens as the active progesterone-like component.
In contrast to some of the progestogens such as medroxyprogesterone acetate (Provera®, Cycrin®) natural progesterone does not seem to suppress good cholesterol (HDL), has no effect on blood pressure or mood, and shows less of a tendency to cause increased male-hormone-like effects such as facial hair growth. Each synthetic progestogen may have a somewhat different side-effect profile so it is not easy to generalize.