Kuijpers SME, Wiepjes CM, Conemans EB, et al. - In this European Network for the Investigation of Gender Incongruence, a multicenter prospective cohort study, researchers sought to evaluate the lowest effective dose of cyproterone acetate (CPA) in trans women to prevent side effects. The study included 882 trans women who took estrogens alone or in combination with 10 mg, 25 mg, 50 mg, or 100 mg CPA daily. Using only estrogens (no CPA) resulted in testosterone concentrations of 5.5 nmol/L (SEM 0.3). With increasing CPA doses, higher prolactin and lower high-density lipoprotein concentrations were observed. There were no differences in liver enzyme concentrations between the doses. In comparison to higher doses of CPA, a daily dose of 10 mg is equally effective in lowering testosterone concentrations in trans women while causing fewer side effects.