Previously:

Disclaimer: I am not a medical professional and this is not medical advice.

Cyproterone acetate (CPA) is an oral antiandrogen widely used outside the United States (Angus et al., 2019) as a part of feminizing HRT in combination with estrogen. In recent years, increasing evidence has emerged that long-term or high-dose use of CPA, such as in transition treatment for transfeminine people, is associated with a substantially elevated risk of developing meningiomas (Gil et al., 2011). These typically benign brain tumors can cause symptoms such as vision loss, headaches, muscle weakness, and seizures, and can require treatment with radiation or surgery.

The mechanism of CPA’s role in promoting the growth of these tumors is well-understood. CPA is an antiandrogen that occupies androgen receptors as an antagonist to block the binding of androgens like testosterone and prevent them from producing physically masculinizing effects, while also functioning as an antigonadotropin to direct the body to stop producing and releasing androgens. However, CPA is not only an antiandrogen – it’s also a progestogen, binding to progesterone receptors as an agonist and producing a very strong progestogenic effect. Additionally, the antiandrogenic and progestogenic effects of CPA are imbalanced, and so the doses needed to suppress testosterone in transfeminine people also produce a significant excess of progestogenic activity (Hammerstein, 1990). Continue reading →