Cyproterone acetate

Cyproterone acetate (CPA; brand name Androcur among others) is a dual steroidal antiandrogen and progestogen.

Mechanism of action
CPA has potent antigonadotropic effects via activation of the progesterone receptor and is able to reduce testosterone levels by up to 70 to 80% at dosages that are sufficiently high. In addition to its antigonadotropic effects, the drug also directly binds to and blocks the androgen receptor. It is notable that CPA is not a silent antagonist of the AR but rather is a very weak partial agonist. In other words, it acts mostly as an antagonist of the receptor, but retains some capacity to activate it, and this can be observed clinically under certain circumstances. CPA also has weak glucocorticoid effects, which contributes to its side effect profile.

Lower doses of CPA (5 to 25 mg/day) are able to markedly suppress testosterone levels similarly to higher doses (25 to 300 mg/day).

Side effects
It can cause side effects such as adverse mental health effects like depression, anxiety, fatigue, and suicidal thoughts, elevated liver enzymes, and vitamin B12 deficiency. In addition, rarely, it can cause liver damage and failure, excessively high prolactin levels, meningiomas, and blood clots.