CJ Bellwether@2d I dont recommend it out of the gate for others purely out of abundance of caution of that uncertainty as there arent any studies on transfems taking progesterone so it has to be peoples personal decision - but i will say the one study that fear hinges upon is pretty bunk in that they gave rabbits an absurd amount of medroxy for average body size of a bunny, and thats a synthetic progestin known to cause breast cancer due to having a high proliferative cell effect while bio-identical/micronised prog has a pro-apoptotic or neutral effect so for caution.
I personally started progesterone about 2 months and 1 week into HRT - 200mg rectally and the 2 months part was just on Pueraria Mirifica off Amazon (which turned out to be real and actually surprisingly did work and got me to tanner 2). Prog definitely did not seem to stop my breast development or lead to shape issues at all as i went from cup size measurements of AA to DD (bust 33.5 inches to 42 inches) over the following 3+ years. But i have no version of me who waited another 9-10 months to compare it to. Shape ended up round and full tanner growth.
For me part of the usage of progesterone was most important as an anti-androgen as i was doing estrogen monotherapy with prog and transdermal estradiol only which brought my testosterone down to 3 nmol/L or 86 ng/dL by month 3.
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