About cyproteronea synthetic derivative of 17-hydroxyprogesterone, androgen receptor antagonist, antiandrogen.mechanism of action of cyproteronethe drug exerts its action by acting as an anti-androgen. it blocks the normal activity of the androgen by competing with dihydrotestosterone for the intracellular androgen receptor sites and inhibits it`s binding. it also has mild progestational activity. being structurally similar to testosterone it itself attaches to surface receptors in prostate cancer cells and thus blocks the attachment of testosterone.indications for cyproterone1. contraception 2. hirsutism 3. male to female transsexuals 4. hyper sexuality 5. prostate cancer