Androgen is a wrong word because all the so called androgens are also existing in women. Did you know that a woman has usually more Testosterone than Estrogen in her body? And younger women have more than older men? Its really fascinating once you look into it. The distinction of Testosterone = Man and Estrogen = Woman is a fairytale, both hormones exist in both and are needed in both.
The people I spoke with used estrogen only from the beginning - no antiandrogens ever, not even for some months. Although for some this was the standard therapy so they had CPA for a while and then stopped. I cannot describe details here because of the rules (no dosages etc...), but it does work with slightly higher estradiol than recommended by many endocs - although many other endocs are totally fine with those dosages as they are far from crazy high. Just the maximum dosage of patches usually works fine with most.
the mechanism , as you mention GNRH , is this:

As you can see, the hypothalamus (GNRH) and pituary gland (LH and FSH) do regulate the bodys hormones. If there is not enough Tesosterone in the body, it will ramp up production until it registers enough testosterone again. This is regulating testosterone production and blood levels in males. However the glands do not care if it is testosterone or estrogen. For women it is more complex but essentially also there more estrogen and progesterone in the blood means less LH and FSH and thus a downregulation of internal hormone production. Now the neat thing is - since the glands do not distinguish that much between testosterone and estrogen, they give the signal "I am full" when one of the two is high enough - and reduce LH and FSH and GNRH and thus the bodys own hormone production. This is why estrogen (maybe in combination with progesterone) alone almost always wil suppress T.
[this is a VERY simplified version of what is happening, so please do not be thrown off if you read about some details being different elsewhere, especially regaring the female hormone system which obviously is cyclical]
Now what many trans women seem to seek however is demaskulinization - no libido and erections anymore, reduced body hair etc. This often is reached only if you drop testosterone levels below that which is normal for females. So then, antiandrogens are loved because they can do that, but beware of the price - remember also women have a libido and life without it is not that great and that testosterone is also important for muscle growth (including growing new muscles in a more feminine shape) and many other body functions. When yout pubic hair starts to become very thin, its a warning sign, since only old and very young women have little pubic hair (unless you remove it of course

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Richenda - your description was warning signs placed over it in my eyes. Please let a doctor do your blood tests soon - and be sure to measure prolactin! Lactating may be somewhat fun and a nice affirmation of being female, but it is also a sign of elevated prolactin levels usually and this is not healthy. Antiandrogens are known to increase the prolactin, especially Androcur which can cause Prolactinoma, a tumor of the pituary gland that produces prolactin.
Last but not least - be very careful with long term use of DHT blockers. There are massive reports about ill side effects of this. Google it. It can even cause some slight forms of dementia. Again, blocking out all and every "androgen" in the body is counterproductive as the female body also needs some of those hormones. Also be aware that progesterone is a soft DHT inhibitor. I and some others I know use Progesterone Gel on the temples and top of the head and it regeneratesd hair growth as it also reduces DHT production. (it is a 5 alpha reductase inhibitor).