GnRH Agonist
A GnRH agonist is a medicine that switches off the testes' or ovaries' own hormone production by overstimulating the signal from the brain until it stops responding. In feminizing hormone therapy it is used as a powerful [anti-androgen](/glossary/anti-androgen). Triptorelin, goserelin and leuprorelin are the common ones.
Where you'll meet it
In the UK, where some NHS gender services prefer it to cyproterone, and in some private and specialist clinics elsewhere. It is given as an injection or an implant under the skin, every month or every few months.
How it works
The name stands for gonadotropin-releasing hormone, the brain's signal to the testes or ovaries. A GnRH agonist mimics that signal so strongly and constantly that the pituitary gland stops passing it on. For the first week or two, before that happens, hormone levels can briefly rise; after that, production drops very low.
The trade-offs
It is effective and avoids the side effects of the tablet anti-androgens, but it is expensive, needs regular injections, and funders do not always cover it. Because it lowers the body's own sex hormones so completely, estrogen alongside it is essential for bone health, not optional.
Related pages
Not sure where to begin?
The Start Here guide covers what hormones change, how people get a prescription, what the blood tests are for and what it costs.
start here →