Literature on the efficacy and safety of gender-affirming hormonal treatment (GAHT) in transgender people is limited. For this reason, in 2010 the European Network for the Investigation of Gender Incongruence (ENIGI) study was born. The aim of this review is to summarize evidence emerging from this prospective multicentric study and to identify future perspectives. GAHT was effective in inducing desired body changes in both trans AMAB and AFAB people (assigned male and female at birth, respectively). Evidence from the ENIGI study confirmed the overall safety of GAHT in the short/mid-term. In trans AMAB people, an increase in prolactin levels was demonstrated, whereas the most common side effects in trans AFAB people were acne development, erythrocytosis, and unfavorable changes in lipid profile. The main future perspectives should include the evaluation of the efficacy and safety of non-standardized hormonal treatment in non-binary trans people. Furthermore, long-term safety data on mortality rates, oncological risk, and cardiovascular, cerebrovascular and thromboembolic events are lacking. With this aim, we decided to extend the observation of the ENIGI study to 10 years in order to study all these aspects in depth and to answer these questions.
Keywords: ENIGI; gender dysphoria; gender incongruence; gender-affirming hormonal treatment; prospective cohort study; transgender.