Hrt has actually corrected a hair loss problem I was having (though feminine as I still had my hairline) and has brought my hair in thicker, fuller, and it's growing like a weed! It's down to the middle of my back now, and I recently had to throw away my smaller hair ties for larger ones so I can keep wearing pony tails when I want to. And this is only 2 months and almost 3 weeks in. I look forward to a full head of hair again after a year as I have alot of new growth that's thickening and coming in nicely. In fact, I already need a trim again after only 3 months!
Alot does depend on the type of hrt meds your taking especially the antiandrogens. My advice would be to talk with your Endochronologist about it and she/he will get you on the right stuff to help your hair come in and grow. It will grow faster if you keep the dead ends trimmed though and use quality hair products ie: shampoos, conditioners, etc., and use a good hair, skin and nails multi. My hair is very important to me not just because I'm in transition (MTF), but I'm full blood Native American as well. Baldness if kind of frowned upon among my people.
Hope this helps ya a little.