Context
Cyproterone acetate (CPA) is a competitive inhibitor of the androgen receptor and exerts negative hypothalamic feedback. It is often used in combination with estrogens in trans women to achieve feminization. However, CPA has been associated with side effects such as changes in liver enzyme concentrations and increases in prolactin concentrations. The question is whether testosterone lowering, as well as these side effects, are dose-dependent.
Objective
To assess the lowest effective dose of CPA in trans women to prevent side effects.
Design
This longitudinal study is part of the European Network for the Investigation of Gender Incongruence (ENIGI), a multicenter prospective cohort study.
Setting
Gender identity centers in Amsterdam, Ghent, and Florence
Participants
Trans women (n = 882) using estrogens only or in combination with 10mg, 25mg, 50mg, or 100mg CPA daily.
Intervention
Different doses of CPA.
Main Outcome measure
The concentration of testosterone at 3 and/or 12 months of hormone therapy.
Results
Using estrogens only (without CPA) led to testosterone concentrations of 5.5nmol/L (SEM 0.3). All doses of CPA resulted in testosterone concentrations below the pre-defined threshold of suppression of 2nmol/L (10mg: 0.9nmol/L, SEM 0.7; 25mg: 0.9nmol/L, SEM 0.1; 50mg: 1.1nmol/L, SEM 0.1; 100mg: 0.9nmol/L, SEM 0.7). Higher prolactin and lower high-density lipoprotein concentrations were observed with increasing doses of CPA. No differences in liver enzyme concentrations were found between the doses.
Conclusions
Compared to higher doses of CPA, a daily dose of 10mg is equally effective in lowering testosterone concentrations in trans women, while showing fewer side effects.