Anti-Androgens for Transgender Individuals in the UK
The most commonly prescribed anti-androgens for transgender women in the UK are spironolactone and cyproterone acetate, used alongside estrogen to suppress testosterone to female range (<50 ng/dL), though neither is specifically licensed for transgender hormone therapy in the UK. 1
Specific Anti-Androgens Used
The primary anti-androgen options include:
- Spironolactone: Aldosterone antagonist with anti-androgenic properties
- Cyproterone acetate: Progestogenic anti-androgen with direct receptor blocking effects
- GnRH analogues (gonadotropin-releasing hormone agonists): Suppress gonadal testosterone production at the hypothalamic-pituitary level
These are prescribed as adjunctive therapy with estrogen to enable lower estrogen doses while achieving adequate testosterone suppression 1, 2.
How They Are Used
For transfeminine individuals, the treatment algorithm follows this approach:
- Anti-androgens are co-prescribed with estrogen (not used alone)
- The goal is to reduce endogenous testosterone levels to the female range (<50 ng/dL)
- This combination produces feminizing physical changes: breast development, decreased facial/body hair, and feminized body composition 3, 1
- The anti-androgen component blocks both testosterone production and receptor binding 3
Mechanism of action varies by agent:
- Spironolactone blocks androgen receptors peripherally
- Cyproterone acetate provides both receptor blockade and central suppression
- GnRH analogues suppress testosterone production at the source 1, 2
UK Licensing Status - Critical Caveat
None of these anti-androgens are specifically licensed for transgender hormone therapy in the UK. This represents off-label prescribing, which is standard practice in transgender medicine globally. The medications are licensed for other indications (spironolactone for hypertension/heart failure, cyproterone for prostate cancer, GnRH analogues for precocious puberty or prostate cancer) but are used off-label for gender-affirming care 2, 4.
This off-label use is supported by:
- International endocrine society guidelines recommending these agents
- Evidence showing safety and efficacy when properly monitored
- Documented improvements in quality of life and reduction in gender dysphoria 2, 5
Important Clinical Considerations
Finasteride (5α-reductase inhibitor) has unclear benefit in transfeminine individuals once testosterone is already suppressed with standard regimens, and should not be considered a first-line anti-androgen 6.
Monitoring requirements include:
- Regular testosterone and estradiol levels
- Cardiovascular risk assessment (particularly with cyproterone)
- Thromboembolic risk evaluation (especially in older patients or those with risk factors) 4
- Liver function monitoring with cyproterone acetate
Physical effects are substantial: Studies show 3-5% decrease in lean body mass, 4-5% reduction in muscle cross-sectional area, and sustained breast development over the first three years of therapy 1.
The evidence consistently demonstrates that when properly prescribed and monitored, these anti-androgen regimens are safe and effective for achieving gender-affirming physical changes, despite the lack of specific UK licensing for transgender use 2, 4, 5.