Effects of testosterone therapy on constructs related to aggression in transgender men: A systematic review

Transgender men are assigned female sex at birth, but identify as men. The anabolic and androgenic sex hormone testosterone has been positively associated with aggression. Therefore, transgender men are warned of increasing aggression when initiating testosterone therapy.

To explore the literature regarding the effects of testosterone therapy on aggression-related constructs in transgender men.

Following PRISMA-guidelines, PsycINFO, MEDLINE®, EMBASE, and PubMed® were searched in November 2019. Risk of bias was analyzed using the Newcastle-Ottawa-Scale, and result-synthesis was grouped by aggression-outcome.

Seven prospective cohort studies investigating aggression-dimensions pre- and post-testosterone therapy, reporting on data from 664 transgender men, were eligible. The studies had moderate to high risk of bias due to non-randomization, lack of appropriate control groups, and reliance on self-report. The behavioral tendency to react aggressively increased in three studies out of four (at three months follow-up), whereas only one study out of five found angry emotions to increase (at seven months follow-up). In contrast, one out of three studies reported a decrease in hostility after initiation of testosterone therapy. The remaining studies found no change in aggressive behavior, anger or hostility during hormone therapy.

Four out of seven studies reported an increase in aggression-related constructs, while one study reported a decrease. In all studies reporting changes, the follow-up period was less than 12 months, indicating that gender-affirming testosterone therapy could have a short-term impact on aggression-related constructs. However, the available studies carried a risk of bias, which indicates a need for further research.