My personal experience (and one I've heard from a lot of other transmen) is that I became a lot calmer, happier, and less emotionally volatile on T. I definitely don't cry as easily, I don't get angry as easily, and I am much less depressed.
When I first went on the Pill, back when I was living female, I was initially put on a low-dose version, (Yasmin) and that made me really crazy. I felt as if I was PMSing 24/7 all month long. Same thing a couple years later when a doctor insisted on putting me on another low-dose pill, (Ortho-tricyclene Low) even after I related my original experience.
On regular Ortho-Cyclene, however, I did fine.
So, yeah, hormones can definitely effect your mood/mental health. If you are really worried about it you might ask your doctor to prescribe topical T. That way, if you have a negative reaction you can stop right away. You also may want to consider starting out with a lower dose of T. Sometimes the "standard" dose can lead to your T levels being too high, at which point the T aromatizes (sp?) into E, which can make it really difficult to keep your hormone levels balanced correctly. There is a school of thought that the ideal dose for most transmen is actually 1/2 to 1/3 of the usual dose prescribed in the U.S. As usual, YMMV.
