A Case of Mistaken Identity: Progestin vs Progesterone
Progesterone. Progestogen. Progestin. There is much confusion, even among experts in the field of hormone research, surrounding the names of these hormones and chemicals, and this misunderstanding is dramatically affecting the lives of millions of women. Let’s try to clear up some of the madness.
Progesterone is the name of a hormone that is endogenously produced in men and women, although it is much more prevalent in women. This is the hormone that predominates during the second half of the menstrual cycle and of course during pregnancy. It gets its name from promoting gestation. Progesterone is also the name used for hormones that are produced from plant sources that have a molecular structure that is identical to the hormone found in the body.
Progestins are synthetic molecules, found nowhere in human physiology or elsewhere in nature, that interact with progesterone receptors in the body and through those receptors exert some partial effects of progesterone. Because these molecules are foreign, many of the side effects and the effects of their metabolites are harmful.
Progestogen is a general term for compounds, both natural and synthetic, with a steroid hormone structure that allows them to attach to progesterone receptors. Both bioidentical progesterone and synthetic progestins fall into this broad category.
Seems pretty straightforward, doesn’t it? Not so fast. It appears that the difference between progesterone, progestogens, and progestins is still not appreciated, as they are often used interchangeably in the literature. The confusion that arises for health care providers when interpreting research findings that reference progesterone and progestins would be reduced if a consistent name was utilized. Because of the inconsistency, it is up to the reader to be educated about the differences.
Progesterone (which is by definition a bioidentical molecule) is not very well absorbed when taken orally. For this and other reasons, a number of synthetic molecules have been developed to mimic the actions of progesterone. Medroxyprogesterone acetate (Provera), norethindrone, norgestimate, levonorgestrel, and drosprirenone are just some of the names of these chemicals that are used in contraception and in hormone replacement.
A number of studies, including the Woman’s Health Initiative, have indicated that the study groups who are given estrogen along with a progestin have an increased risk of breast cancer and cardiovascular disease over their counterparts who are given estrogen alone. Because of the confusion in nomenclature, these findings have prompted some regulatory bodies to require that all progestogens carry a warning label stating that there may be an increased risk of cancer and other conditions with the use of these products. Remember the old adage “Don’t throw the baby out with the bathwater?” This classification mix up is far from harmless, as there is ample evidence to support that progesterone, when given alone or in combination with estrogen, is protective to the breasts and the cardiovascular system. Progesterone exerts several anti-cancer mechanisms on tissues and millions of women may be excluded from this benefit due to mistaken identity.
It is essential that health care providers stay educated about the differences between these very different substances. Understanding the many benefits of progesterone and the detriments of progestins can be of profound benefit to health and longevity.