To protect the uterine lining from continuous stimulation by estrogen, most physicians prescribing standard ERT combine it with Provera®. If you ask them if it is progesterone, they’ll probably even tell you it is—it is not. It is medroxyprogesterone acetate, which is natural progesterone altered by the addition of a molecule to make it patentable and more orally absorbable. This molecule alters Provera’s effect on tissues other than the uterus.
Many women discontinue ERT because they don’t like the way it makes them feel—irritable and often depressed. In contrast, bioidentical micronized progesterone is often called the feel-good hormone because it elevates mood and is calming. Women who have experienced mood swings and migraine headaches on Provera® often notice complete resolution of these symptoms when switched to bioidentical progesterone. In addition, bioidentical progesterone was found to have the best effect on HDL cholesterol in the PEPI trial. This trial is the largest to date to include bioidentical micronized progesterone. Unfortunately, the WHI did not include an arm with progesterone, only Provera®. If it had, we think the results would have been very different. Bioidentical progesterone can also act as a natural diuretic, in contrast to Provera® which often causes fluid retention and bloating.
There is, however, an even more compelling reason to avoid using Provera®. It comes from recent studies by a number of different researchers, and thus is unlikely to be disproved. These researchers showed that Provera® can reverse by 50% the coronary artery-dilating effect of estrogens and that progesterone does not have this negative effect.
This may explain the results of the HERS trial that is often quoted in the press as showing that estrogen does not protect the heart as was thought. In this large, prospective trial, the progestin used was Provera®, not progesterone. The early slight increase in heart attacks in women with established cardiovascular disease could have resulted from the negative effect of Provera® on the coronary arteries. (The other probable reason for the increase in heart attacks in the first year of therapy is that the oral estrogen caused a greater propensity to clotting and in women with arteries already narrowed from atherosclerosis this can cause coronary clots--heart attacks.)
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