Ok folks, many doctors are afraid to prescribe P for transwomen because they claim, and perhaps rightly so, that there are no formally-recognized proven studies that indicate that P actually works. Yes, perhaps, but there are also no formally-recognized proven studies that indicate that P does not work.
P is designed to help with the maturation of breast development in transwomen. in natal females, P levels play a major role in the menstruation cycle.
The most common rule of thumb i have seen suggests that transwomen not start P immediately, but go with just estrogen for a period of 2 years post-op (or post-orchi). if suitable breast development hasn't occurred, then introduce P. go with Prometrium - which is natural, if you can get your hands on it.. as synthetic provera / microgest has more risk of side affects.
in just 10 months on P (including 3 on synthetic and 7 on natural), i have seen significant maturation of breast development, as they have gone from cone shaped to breast shaped. i have also seen my areolas double in size. my nipples have only grown slightly. but the overall mass has grown so much that i literally have stretch marks all over my breasts!
rule of thumb suggests that i should stay on P for 2-3 years, and that should max out what it can do for me.
side affects of P - further challenges of what estrace does - loss of strength, speed, energy, worse metabolism - body weight gain (38 pounds in 10 months). and emotional issues such as masculine-like rage or temper tantrums.
but yes, it does work, at least it did for me!!!