It seems a little silly to make a thread just about this (sorry!) but I came across this very interesting study earlier. It seems to tie in with feminist concerns around transgender males in sports - and in situations where women are vulnerable - and I haven't seen it linked before 
Apologies if it has been!
Only a quarter of transgender women taking a regimen of spironolactone and estrogens were able to lower testosterone levels within the usual female physiologic range. Another quarter could not achieve female levels but remained below the male range virtually all of the time, while one quarter was unable to achieve any significant suppression.
www.sciencedaily.com/releases/2018/02/180220143424.htm