I'll have to try biotin again. A doctor had recommended it a while back, and I ended up buying a hair and nail vitamin product from a health food store. It didn't help, but I may have better results if I try a higher concentration of biotin. I used to think it was caused by the spiro, but I don't take it any more, so it must be caused by the estrogen. I'll buy the 5,000 mcg and see how it works.
My nails were bad before SRS, afterwards, they became much worse. Spiro had little efffect on me, virtually no breast growth or other changes. After SRS, breast growth was suddenly taking place, and there were other physical effects too. Even though I'm post-op, my doctor did not lower the dosage of estrogen. The clinic that administers my HRT generally maintain the pre-op estrogen dosage for at least 2 years post-op. It's a protocol that's worked very well for me because the estrogen can work virtually unopposed by testosterone.
One way of thinking is breast growth occurs either in a growth or a non growth phase, and in natal females, breast growth can take 5 years or more. As long as breast growth or other feminization is taking place, unless there are increased side effects, there is no reason to change the dosage of estrogen. Unfortunately, the increased function of estrogen also causes an increase in the weakening of fingernails as a side effect in some people. It's a trade off, but I'd prefer to have the desired gains and I'll try the biotin to deal with the thin fingernails.
The traditional way of administering HRT is to lower the dosage of estrogen by at least 50% post op, but that originated when a different form of estrogen was used in HRT, the other form being more prone to serious side effects such as blood clots in the legs. HRT as typically administered today is considered to have a higher safety factor, so maintaining the pre-op dosage, which still must be monitored on a regular basis, is thought to be less hazardous. It may be due to the lowering of estrogen post-op as well as spiro being a weak anti androgen compared to surgery, that problems with thin and brittle fingernails isn't more prevalent.