In the large WHI study, Provera use was associated with an increase in clots, stroke, cardiovascular incidents and breast cancer. Progesterone use, in another study, was not associated with an increase in breast cancer.
Just a few studies:
Nat Med. 1997 Mar;3(3):324-7.
"Cardiovascular disease, the major cause of death in post-menopausal women, can be reduced by replacement of ovarian steroid hormones. To compare medroxyprogesterone with progesterone as the progestin in hormone replacement therapy from the standpoint of coronary artery vasospasm, we treated ovariectomized rhesus monkeys with physiological levels of estradiol-17 beta in combination with medroxyprogesterone or progesterone for four weeks. Coronary vasospasm in response to pathophysiological stimulation without injury showed that progesterone plus estradiol protected but medroxyprogesterone plus estradiol failed to protect, allowing vasospasm. We conclude that medroxyprogesterone in contrast to progesterone increases the risk of coronary vasospasm."
International Journal of ->-bleeped-<-, 13:165–232, 2011
"Progestins (especially medroxyprogesterone) are also suspected to increase breast cancer risk and cardiovascular risk in women (Rossouw et al., 2002). Micronized progesterone may be better tolerated and have a more favorable impact on the lipid profile than medroxyprogesterone does (de Lignieres, 1999; Fitzpatrick, Pace, & Wiita, 2000)."
Endocrine Reviews, April 2013, 34(2):171–208
"Recent results suggest that MPA, acting via
transactivation of the GR on target genes such as the fatty
acid synthase gene, may promote tumorigenesis in normal
cells and cancer progression in cancer cells, unlike progesterone
(195). »
MPA = medroxyprogesterone acetate (Provera)
Journal of the Gay and Lesbian Medical Association, Vol. 4, No. 4, 2000
"Micronized progesterone (Prometrium) is advantageous because it has a more favorable side effect profile (anxiety and irritability) than medroxyprogesterone."
Horm Behav. 2013 Feb; 63(2): 284–290.
"Here, we review the evidence that supports the neuroprotective effects of progesterone and discuss the various mechanisms that are thought to mediate these protective effects. We also discuss the receptor pharmacology of progesterone's neuroprotective effects and present a conceptual model of progesterone action that supports the complementary effects of membrane-associated and classical intracellular progesterone receptors. In addition, we discuss fundamental differences in the neurobiology of progesterone and the clinically used, synthetic progestin, medroxyprogesterone acetate that may offer an explanation for the negative findings of the combined estrogen/progestin arm of the Women's Health Initiative-Memory Study (WHIMS) and suggest that the type of progestin used may dictate the outcome of either pre-clinical or clinical studies that addresses brain function."
Maturitas. 2015 Mar 9.
"In a cross-sectional study of 176 women who had previously switched from HT containing MPA to HT containing micronized progesterone, 71% had switched because of the better side effect profile, 35% because they believed the long-term risks would be fewer, and 23% because of intolerance to MPA [21]. When evaluated at 1 to 6 months after switching, the women experienced significantly better quality of life, including less depression and anxiety, than with MPA (both P < 0.001) [21]. Patient satisfaction questionnaires also indicated that women preferred micronized progesterone over their previous regimen for better symptom control and fewer adverse effects (P < 0.001) [21]."
"Sleep was significantly improved after 6 months of CEE plus micronized progesterone but not with CEE plus MPA in a randomized study of 21 postmenopausal women tested in a sleep laboratory [22]."
CEE = conjugated equine estrogens (Premarin)
HT = hormone therapy
"Progesterone stimulated nitric oxide synthesis and inhibited adhesion of platelets to endothelial cells in rat endothelial cell cultures, whereas MPA inhibited nitric oxide synthesis and increased platelet adhesion [48]. »
Trends in Endocrinology and Metabolism
Volume 11, Issue 2, 1 March 2000, Pages 69–71
"Curiously, addition of the synthetic progestin, medroxyprogesterone, blocked the modulating effects of oestrogen on serotonin activity, while natural progesterone did not."
Climacteric. 2013 Aug;16 Suppl 1:44-53.
"Estrogen probably adds some cardioprotection, that can, however, be obscured by progestogens, especially medroxyprogesterone acetate (MPA)"
"Natural, 'body-identical' progesterone, devoid of any androgenic as well as glucocorticoid activities but being slightly hypotensive due to its antimineralocorticoid activity, appears to be the optimal progestogen in terms of cardiovascular effects, blood pressure, VTE, probably stroke and even breast cancer »
Etc.
