I'd say its because Premarin is not truly estrogen and there's health risks in taking it. The name of it might be a matter of terminology, but human estrogen is chemically different to horse estrogen. I'd imagine the new estrogen is bio-identical to human estrogen.
While I can't argue with your experience and medicine is not my field, I can't help but think there must have been something wrong with the approaches you were taking before. I don't see how Premarin could work and a correct HRT regime could fail.
Personally I'd not take it and stayed well away from one place in Sydney that prescribes it. I believe it shows they don't know what they are doing (in general I have little respect or trust for doctors, that's got to be earned). Also, the company that makes Premarin is making a lot of money off it and are hardly likely to withdraw it from the market when something better comes along. More likely they will continue to market and promote it, much like tobacco companies would.
I've a few ideas.
Have you been doing blood level measurements, and if so are they in the correct range? How do you know the range is correct? Estrogen and testosterone levels in particular, but there's a pages and pages of them in the report that my endo does (most of them are looking for other health issues though). Dosages are not as important, and also can't be discussed on this site.
I'd also question the doctors expertise. If this is the same doctor that had you on Premarin I'd start looking for a new one, and not one that prescribes Premarin. Look for an endocrinologist that specialists in transgender medicine and is hopefully well regarded.
If you were doing DIY before this might have been a reason it didn't work.
I could be completely wrong of course, but I find it's an interesting topic and I'd certainly like to see some discussion on it.
