Cyproterone acetate or spironolactone in lowering testosterone concentrations for transgender individuals receiving oestradiol therapy

Background Oestradiol with or without an anti-androgen (cyproterone acetate or spironolactone) is commonly prescribed in transfeminine individuals who have not had orchidectomy; however, there is no evidence to guide optimal treatment choice. Objective We aimed to compare add-on cyproterone acetate versus spironolactone in lowering endogenous testosterone concentrations in transfeminine individuals. Design Retrospective cross-sectional study. Methods We analysed 114 transfeminine individuals who had been on oestradiol therapy for >6 months in two gender clinics in Melbourne, Australia. Total testosterone concentrations were compared between three groups; oestradiol alone (n = 21), oestradiol plus cyproterone acetate (n = 21) and oestradiol plus spironolactone (n = 38). Secondary outcomes included serum oestradiol concentration, oestradiol valerate dose, blood pressure, serum potassium, urea and creatinine. Results Median age was 27.0 years (22.5–45.1) and median duration of hormone therapy was 1.5 years (0.9–2.6), which was not different between groups. On univariate analysis, the cyproterone group had significantly lower total testosterone concentrations (0.8 nmol/L (0.6–1.20)) compared with the spironolactone group (2.0 nmol/L (0.9–9.4), P = 0.037) and oestradiol alone group (10.5 nmol/L (4.9–17.2), P