>We conducted a systematic literature review of all peer-reviewed articles published in English between 1991 and June 2017 that assess the effect of gender transition on transgender well-being. We identified 55 studies that consist of primary research on this topic, of which 51 (93%) found that gender transition improves the overall well-being of transgender people, while 4 (7%) report mixed or null findings.
>We found no studies concluding that gender transition causes overall harm.


https://whatweknow.inequality.cornell.edu/topics/lgbt-equality/what-does-the-scholarly-research-say-about-the-well-being-of-transgender-people/