Soundbite: progestin is NOT progesterone. The whole HRT scam needlessly subjected millions of women to the risk of catastrophic health problems in order to profit from a patentable synthetic concoction marketed as if it was the real thing.
The first report on the halted WHI estrogen-plus-progestin study came out in July 2002. It followed over 16 000 women for an average of 5.2 years, half of which taking a placebo, the other half taking PremPro, a combination of the progestinmedroxyprogesterone acetate and conjugated equine estrogens. The study found statistically significant increases in rates of breast cancer, coronary heart disease, strokes and pulmonary emboli. The study also found statistically significant decreases in rates of hip fracture and colorectal cancer. “A year after the study was stopped in 2002, an article was published indicating that estrogen plus progestin also increases the risks of dementia.”  The conclusion of the study was that the HRT combination presented risks that outweighed its measured benefits. The results were almost universally reported as risks and problems associated with HRT in general, rather than with PremPro, the specific proprietary combination of conjugated equine estrogen and progestin studied. ….
Progesterone is a steroid hormone produced by the adrenal gland in both men and women, the testes in men and the ovary in women. It plays a role in the female menstrual cycle and pregnancy and circulates throughout the body binding to receptors in the brain, the cardiovascular tissue, breast tissue and more. Progesterone is also a precursor to other important hormones in our body- cortisol, aldosterone, testosterone and estradiol.
Progestins are a synthetic progestogens that bind some progesterone receptors in the body, but not all. They were produced first in 1938 in hopes of finding a patentable drug that could work like progesterone in the body. While chemically similar to progesterone, they are not identical, and this makes them patentable.
Since Progestins and Progesterone are different molecules they have different effects on the body. As a general rule, synthetic progestins are more potent that bio-identical progesterone. They have a longer half life than progesterone, have greater relative binding affinities and have been found to have a stronger affect on the endometrium at lower doses than progesterone. Thus -more potent. Progestins also can have androgenic qualities like increased facial hair growth while progesterone can be used as a treatment to reduce this symptom.
The metabolism of these two hormones differs quite a bit. Metabolites of progesterone are well known and include dihydroprogesterone, pregnenolone, pregnanediol and their isomers. Progesterone metabolites can be found in feces, urine, saliva and blood. Less is known, however, about the metabolism of progestins. One thing we do know is that progestin metabolites while fewer in number, have biologic activity themselves. Norethindrone in fact metabolizes to ethinyl estradiol increasing that total amount of ee that an individual is exposed to in combined HRT.
It’s a very common mistake among health care professionals to use the terms progesterone and progestin interchangeably. But this mistake can be deadly. We know now that progestins have an unfavorable effect on the cardiovascular system while progesterone can be used to treat and prevent cardiovascular disease. A great review of this can be found in the Hermsemeyer et al article “cardiovascular effects of medroxyprogesterone acetate and progesterone: a case of mistaken identity?”
Progesterone protects against estrogen-induced breast cancer, as seen in the following study in the http://aje.oxfordjournals.org/cgi/content/short/114/2/209 and as outlined in Dr John Lee, David Zava and Virginia Hopkins book “what your doctor may not tell you about breast cancer”. Synthetic progestins when combined with estrogen increase a woman’s risk of breast cancer. Recent studies can be seen at these links http://content.nejm.org/cgi/content/abstract/332/24/1589http://jama.ama-assn.org/cgi/content/abstract/283/4/485