Is a lower dose of cyproterone acetate as effective at testosterone suppression in transgender women as higher doses?

ABSTRACT

Objective: The recommended dose of cyproterone acetate (CPA), an anti-androgen that is commonly used in the hormonal treatment of transgender women, is 50–100 mg daily. Our objective was to determine whether CPA at 25 mg daily would suppress total testosterone as effectively as 50 mg daily in transgender women.

Methods: We conducted a retrospective cohort analysis of transgender women attending an endocrinology clinic between April 1, 2009, and June 30, 2015. We used a generalized linear mixed model to compare total testosterone between patients on CPA 25 mg versus CPA 50 mg or higher. In a subgroup of patients for which the CPA dose was decreased from 50 mg to 25 mg, we compared total testosterone levels before and after the decrease.

Results: We divided the sixty-eight patients included in the study into 4 groups: group 1, CPA 25 mg (N =31); group 2, CPA 50 mg or higher (N = 19); group 3, CPA dose lowered from 50 mg to 25 mg (N = 15); group 4, CPA dose increased from 25 mg to 50 mg (N = 3). The mean total testosterone on treatment was 0.9 nmol/L (95% CI 0.7 to 1.1) in group 1 and 1.2 nmol/L (95% CI 0.9–1.5) in group 2 and were not significantly different (p = 0.087). In group 3, there was no significant difference between total testosterone levels before and after decreasing the dose of CPA from 50 mg to 25 mg, p = 0.86. Group 4 was excluded from analysis.

Conclusions: We found that 25 mg of CPA daily was effective at suppressing testosterone levels to within normal female range when used in combination with recommended estrogen therapy in transgender women. Clinicians should consider using a lower dose of CPA in order to minimize potential adverse effects.

KEYWORDS:

• Anti-androgen
• cyproterone acetate
• hormone therapy
• transgender

Declaration of interest

There is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported.

Acknowledgements

Babak Aliarzadeh: statistical analysis; Labeeb Talukder: data collection; Steven Orlov: data base design.

Funding

This research was supported by the Physicians' Services Inc. Foundation and the Toronto East General Community Based Biostatistician Research Fund.