Cyproterone acetate (CPA), sold alone under the brand name Androcur or with ethinylestradiol under the brand names Diane or Diane-35 among others, is an antiandrogen and progestin medication which is used in the treatment of androgen-dependent conditions like acne, excessive hair growth, early puberty, and prostate cancer, as a component of feminizing hormone therapy for transgender women, and in birth control pills. It is formulated and used both alone and in combination with an estrogen and is available for use both by mouth and by injection into muscle. CPA is taken by mouth one to three times per day or given by injection once or twice per week.
Common side effects of high-dose CPA in men include gynecomastia (breast development) and feminization. In both men and women, possible side effects of CPA include low sex hormone levels, reversible infertility, sexual dysfunction, fatigue, depression, weight gain, and elevated liver enzymes. At very high doses in older individuals, significant cardiovascular complications can occur. Rare but serious adverse reactions of CPA include blood clots, liver damage, and certain types of benign brain tumors. CPA can also cause adrenal insufficiency as a withdrawal effect if it is discontinued abruptly from a high dosage. CPA blocks the effects of androgens like testosterone in the body, which it does by preventing them from interacting with their biological target, the androgen receptor (AR), and by reducing their production by the gonads and hence their concentrations in the body. In addition, it has progesterone-like effects by activating the progesterone receptor (PR).