The effect of gender-affirming hormonal treatment on personality traits - a NEO-PI-R study

Gender-affirming hormone therapy is a crucial component of the medical transition for many transgender individuals. While there are well-established differences in personality traits between cisgender men and women, the effects of gender-affirming hormone therapy on these traits in transgender individuals remain largely unexplored.

The primary aim of this study was to investigate whether gender-affirming hormone therapy affects personality traits in transgender individuals.

Adult transgender persons referred for gender-affirming hormone therapy to ANOVA, Center for Andrology, Sexual Medicine, and Trans Medicine at Karolinska University Hospital, Stockholm, Sweden, completed the NEO-PI-R inventory once before starting hormone therapy and once after a minimum of six months of either anti-androgen and estradiol treatment or testosterone therapy. Changes in scores were analyzed using the Wilcoxon Signed-Ranks Test. Patients who had any known hormonal, chromosomal, psychiatric, neurological, or other major medical disorders were excluded from the study.

At baseline, the assigned female at birth (AFAB) had significantly higher NEO-PI-R scores in the dimension "Agreeableness" and the facets E5 "Excitement seeking" and A2 "Straightforwardness" compared to the assigned male at birth (AMAB). With treatment, the AMAB showed an increase in O3 "Feelings" (md = 2.00; IQR = 0.00-11.50; p = 1.5E-02) and the AFAB showed a decrease in "Neuroticism" (md = -2.00; IQR = -5.50-1.00; p = 3.8E-02), N3 "Depression" (md = -3.00; IQR = -8.25-3.00; p = 2.8E-02), and N6 "Vulnerability" (md = -4.50; IQR = -9.00-2.00; p = 90E-03), as well as an increase in "Actions" (median = 4.00; IQR = -2.50-8.00; p = 1.7E-02). After treatment, the greatest difference between the groups was seen in N6 "Vulnerabiliy". In AMAB, significant negative correlations between the change in NEO-PI-R score and the change in estradiol were found in 2 dimensions and 6 facets.

Few changes in personality traits were observed, but they aligned with expectations based on established sex differences in personality traits. In general, more changes were observed in the testosterone treated group. The reduction in "Neuroticism" and "Vulnerability" in the AFAB with treatment, but a worsening or no change in the AMAB may be concerning. Further studies are needed to solidify these results and explore the underlying causes.