Aggression changes during masculinizing and feminizing gender-affirming hormone therapy (GAHT) – A prospective clinical study

Introduction: Testosterone and aggression have been positively associated, but it remains unclear whether gender-affirming hormone therapy (GAHT)-induced testosterone changes affect aggression in transgender persons. This study investigates aggression changes and associations between aggression and testosterone, depression, and anxiety during the first year of GAHT. Methods: Alternative-Short-Aggression-Questionnaire scores were assessed in transmasculine and transfeminine adults at baseline, six weeks, and one year post-GAHT initiation. Cisgender men and women were the comparison groups. Linear mixed effect models evaluated aggression score changes and group-differences, including effects of testosterone, depression, and anxiety, controlling for age and education. Results: Baseline data included 50 transmasculine (median age = 22 years), 62 transfeminine (median age = 24 years), 176 cisgender men (median age = 31 years), and 470 cisgender women (median age = 25 years). Seventy-one percent of transgender participants completed all follow-ups. Total and verbal aggression scores decreased after one year across transmasculine and transfeminine persons (mean difference (MD) = −1.6, p =.018 and MD = −0.8, p =.004), with no changes in other aggression dimensions. At baseline, transmasculine participants showed higher total aggression (MD = 3.4, p =.009) and anger (MD = 1.8, p <.001) scores than transfeminine persons. Transmasculine (MD = 3.3, p =.015) and transfeminine (MD = 6.5, p = <.001) persons had lower total aggression scores than cisgender men. Testosterone was not associated with aggression, whereas anxiety was significantly positively associated with aggression scores. Discussion: There was no GAHT-induced increased aggression in transmasculine persons. Total aggression scores decreased after one year across GAHT-types. Transgender aggression scores were significantly lower than cisgender men, indicating no risk of pathological aggression in the transgender population. Limitations included participant numbers and self-report measures.