Today, confusion swirls about whether supplementing natural progesterone, a hormone made by women’s adrenal glands and ovaries, is safe.
Some of the confusion arises from incorrect interpretation and exaggeration of the original NIH Women’s Health Initiative (WHI) studies. In 2002, NIH abruptly and prematurely stopped the arm of the study in which women were taking Prempro® (Premarin/conjugated equine estrogens/CEE) and Provera® (medroxyprogesterone acetate/MPA) combined. Headlines read “Hormone replacement therapy associated with a 38% increase in stroke risk.”
But, there were many design flaws in the study and the results were misrepresented. That 38% was risk relative to the placebo group. The actual absolute increased risk of a single woman having a stroke increased from 2.4 women per 10,000 women taking placebo to 3.3 women per 10,000 taking Prempro. Real, but not nearly so scary. And yes, an increase from 2.4 to 3.8 is a 38% increase. But the absolute numbers for both are very small.
Even so, physicians told patients to stop HRT. and they did. Around 25% of postmenopausal women were on HRT at that time. This number dropped to 5%.
A belief arose in the lay public's mind that all hormone replacement therapy was dangerous.
However, only 8% of women doctors around the world stopped taking HRT after these headlines were published. 80% of lay users stopped HRT. Female physicians and wives of male physicians use HRT much more frequently and stay on it longer than laywomen.
Progesterone or Progestin?
Researchers call drugs with progesterone-like effects on the uterus progestins or progestogens. A second source of confusion about the safety and utility of progesterone is that progesterone, a naturally occurring female hormone, is almost always categorized with progestins. Most researchers hold the opinion that progesterone and progestins are biologically equivalent. They are considered to be identical and to act the same, but they are not and they do not.
Also, these drugs are then named “progesterone” in published literature. No wonder it’s confusing. A 2011 paper from China repeatedly uses the word progesterone when the study actually utilizes Provera. Researchers worldwide, the Mayo Clinic and journals all lump these drugs together with bio-identical progesterone.
So it’s easy to see why many doctors equate progestins and natural progesterone.