I am very curious about how transgender HRT affects personality. In a sense, HRT is supposed to change who one is, but the personality changes people undergo on it seem underappreciated and not really understood or studied clinically. At least I have not been able to find a published study specifically about about how HRT changes personality. I think not all of it can be attributed to decreased gender dysphoria or people "coming out of their shell" and being able to live and socialize as who they want to be after transition.
If I had to make a $100 bet today on what future research will find, I would wager that
1. FtM HRT reduces Big Five neuroticism despite increasing aggression. The effect is permanent and persists after the person's "second puberty" induced by HRT is over. It affects beliefs about how society should function. To a degree of approximation, it makes transmen more conservative or right-wing than they were before the treatment.
2. MtF HRT does not have the opposite effect to the above (but it may, and probably does, have other effects). Edit: The opposite effect on neuroticism and sociopolitical beliefs. It decreases aggression.
If I had to make a $100 bet today on what future research will find, I would wager that
1. FtM HRT reduces Big Five neuroticism despite increasing aggression. The effect is permanent and persists after the person's "second puberty" induced by HRT is over. It affects beliefs about how society should function. To a degree of approximation, it makes transmen more conservative or right-wing than they were before the treatment.
2. MtF HRT does not have the opposite effect to the above (but it may, and probably does, have other effects). Edit: The opposite effect on neuroticism and sociopolitical beliefs. It decreases aggression.