Cyproterone acetate is an antiandrogen drug used in the treatment of symptoms associated with an excess of androgens, including hirsutism, ovulation problems, and male pattern baldness in women. It is also used in the treatment of prostate cancer.
It may increase the risk of thromboembolic events so the use of oral contraceptives which use this drug in combination with estrogen can bring an increased risk of blood clots.
Cyproterone paired with ethinyl estradiol is used in oral contraceptives that also treat the symptoms of hyperandrogenism in women (such as hirsutism and acne).
Cyproterone acts as an antiandrogen (hence it's usefulness in treating acne and other effects of excess androgen) as well as a weak progestin and brings with it an increased risk of blood clots. Combined with estrogen, with also carries a risk of blood clots, this drug offers an even higher risk of the user developing blood clots.