Back when I was in university we were asked to do a brief research exercise on a health condition impacting a community. Can't remember what I wanted to look at now, but it was something to do with the trans community.
Whatever it was, to put it this way, if there were 10 studies on the trans community as a whole, there were 3 on trans women and trans fems and 0 on trans men and trans mascs, and 0 on nonbinary people. All of the mixed studies were also pretty much useless for my purposes as well because they were all so lopsided.
I think I swapped to a bunch of different things - addiction rates, smoking, depression, mental health in general - nothing that was even roughly equal in looking at all of us. Trans men, trans mascs and nonbinary people are so under researched as to be nonexistent.
To keep this brief since I've rambled a bunch - this is a major issue health wise since we have not a lot of literature on what testosterone does to certain bodies. This can lead to major health complications, not because of the testosterone itself, but because there might be an interaction thats missed or a complication that's not noticed (which is the same for any medication that's under researched on certain bodies. This is not me scaring people off of hrt, this is me pointing out its a medication like any other.)