Abstract
Background: Administration of cyproterone acetate (CPA), to reduce the production and effects of testosterone, is often part of clinical regimens for trans individuals seeking feminization. Due to the potency of CPA, there are dose-related side effects and over-suppression of testosterone that can occur. Aim: This study aimed to determine the lowest possible dosing of CPA to reduce dose-related side effects while still achieving patient goals. Methods: This uncontrolled intervention study recruited participants seeking full-dose feminizing hormone treatment from across six study sites in Australia (primary care and sexual health clinics). Administration of CPA was defined using a titration protocol to achieve the target testosterone range (0.5-1.5 nmol/L). Descriptive analysis was conducted to investigate various factors of interest that pertained to the aims of the study. Results: A total of 74 participants commenced the study. There was a high rate of loss to follow-up with 62.2% (46/74) completing the protocol endpoint. Of participants who completed the protocol, 74.0% (34/46) were able to achieve the target T-range (0.5-1.5 nmol/L) and 41.3% (19/46) were titrated to the lowest CPA level (12.5 mg cyproterone twice weekly). Discussion: This study provided clinical evidence that lower and alternate-day dosing CPA can achieve adequate testosterone suppression in individuals undergoing feminizing gender affirming hormone therapy (GAHT). This provides promising evidence of the acceptability of lowering CPA dosing to reduce the impacts of CPA-related side effects and improve the outcomes and experiences of individuals undergoing GAHT.