[Pansy-Mae]

According to wikipedia normal growth requires both estrogen and progesterone. Maybe there's confusion because estrogen is anti-progesterone and progesterone is anti-estrogen so way too much of only one can reduce the other to the point where you stop.

I think it depends where you are with things and also whether you are starting as a genetic male or female.

During female puberty, estrogen production, and body levels, rise first and start breast development, producing the typical juvenile conical shape breasts often seen in younger teenage girls ( see Tanner Cycle illustrations). Only towards the end of the breast growth period does the female body naturally start to produce progesterone and the cones fill out to the mature rounded shape. Then both progesterone and estrogens are produced cyclically during the month to maintain things and get the body ready in the second half to start milk production if fertilisation has taken place. In a female this should be in balance over the month, but routine over/under production of either, causes a whole raft of symptoms, one of which is small/flat/etc, breasts.

For genetic males trying to develop breasts, aside from suppressing DHT to give things a fighting chance, we need to mimic the natural female process, with estrogens first, and then progesterone right towards the end to round things off ( literally!).

What I'm not sure about is whether you can go estrogen---> progesterone to get small rounded boobs and then back on to estrogen to get them bigger, or if the introduction of progesterone does actually some how permanently stop the ability to grow the underlying breast tissue.