Cyproterone  Cyproterone, also known by its developmental code name SH-80881, is a steroidal antiandrogen which was studied in the 1960s and 1970s but was never introduced for medical use. It is an analogue of cyproterone acetate (CPA), an antiandrogen, progestin, and antigonadotropin which was introduced instead of cyproterone and is widely used as a medication. Cyproterone and CPA were among the first antiandrogens to be developed. It is important to clarify that the term "cyproterone" is often used as a synonym and shorthand for "cyproterone acetate", and when the term occurs, what is almost always being referred to is, confusingly, CPA and not actually cyproterone. Cyproterone itself, unlike CPA, was never introduced for medical use and hence is not available as a medication. Cyproterone is a potent antiandrogen, similarly to CPA. However, it has approximately three-fold lower potency as an antagonist of the androgen receptor (AR) relative to CPA. Like CPA, cyproterone is actually a weak partial agonist of the AR, and hence has the potential for both antiandrogenic and androgenic activity in some contexts. Unlike CPA (which is a highly potent progestogen), cyproterone is a pure antiandrogen and is virtually devoid of progestogenic activity. As such, it is not an antigonadotropin, and is actually progonadotropic in males, increasing gonadotropin and testosterone levels due to inhibition of AR-mediated negative feedback on the hypothalamic–pituitary–gonadal axis. Due to its progonadotropic effects in males, unlike CPA, cyproterone has been found, in male rodents, to increase testicular weight, increase the total number of type A spermatogonia, increase the total number of Sertoli cells, hyperstimulate the Leydig cells, and to have almost no effect on spermatogenesis. Conversely, it has also been reported for male rodents that spermiogenesis is inhibited and that accessory sexual gland weights (e.g., prostate gland, seminal vesicles) and fertility were markedly reduced, although with rapid recovery from the changes upon cessation of treatment. In any case, the medication is said to not be an effective antispermatogenic agent, whereas CPA is effective.