LAUSR

Gender dysphoria in transgender men is generally treated with exogenous testosterone administration aiming to suppress secondary female sex characteristics and achieve masculinization. However, the effect of testosterone on the personality of transgender men remains largely unknown. Therefore, we conducted a controlled study with 23 trans men (M = 27.2 years, Range = 18-51 years), recruited from internet-groups, medical and psychiatric services in Switzerland and Germany versus 27 cisgender women matched by age as control group. Data were collected prior to hormone therapy (HT), three and six months after the first treatment. Non-pathological personality traits (Big Five) were measured with the revised NEO-Personality-Inventory (NEO-PI-R). The greatest changes in the Big Five and its subdimensions occurred within the first three months. Interaction effects showed a significant decrease in the dimension Neuroticism (p < 0.01) - with the most relevant decline in its facet Depression - conversely, Extraversion (p < 0.001) increased, in particular, within its facets of Assertiveness (p < 0.01) and Warmth (p < 0.01). Expectedly, personality traits were stable in the control group. An overall decrease in interpersonal stress-related traits and a substantial increase in enhanced social-interaction traits and personal well-being occurred. These results enable medical services to ensure that informed-consent prior to HT is evidence-based with respect to potential changes in personality and may reduce concerns of trans men and their significant others regarding increased aggressiveness.