Masteron 100 is an injectable steroid made by Dragon Pharma, its active substance is Drostanolone Propionate.
Masteron 100 is perhaps one of the more exotic androgenic / anabolic steroids that may be used by an athlete. Originally it was developed and used as an anti-estrogen for the treatment of breast cancer. It was largely used in combination with the SERM (Selective Estrogen Receptor Modulator) Tamoxifen (Nolvadex) for the treatment of breast cancer, and did give a significant decrease in estrogen levels in women undergoing such treatment. It is not much used these days for such purposes, for varying reasons, however for many athletes including competitive bodybuilders in particular, Masteron 100 remains a rather unsung favourite of anabolic steroid medicines.
The fact that Masteron 100 was being used as an anti-estrogen goes to suggest quite a lot about some properties Masteron 100 possesses. Masteron 100 is a derivative of DHT (dihydrotestosterone) and does not convert to estrogen through means of aromatisation. It is thought that the anti-estrogenic properties of Masteron 100 may be in part to do with either an inhibition in some way of the aromatase enzyme or an interaction with estrogen itself in a way which blocks receptor binding of the estrogen. Either way, this would put Masteron 100 as a useful tool for the anabolic steroid user who uses compounds that convert to estrogen (which most anabolic steroid users do, considering testosterone is the main basis of most cycles).
By inhibiting the aromatase enzyme, Masteron 100 would be in effect blocking the conversion of free testosterone to estrogen by the aromatisation pathway. This would not only serve to marginally increase the amounts of active free testosterone in circulation, but it would also negate the side-effects that result from high levels of estrogen due to aromatisation. Such side effects include the development of gynecomastia and water retention/bloating.
Conversely, if Masteron 100 actually blocks the binding of estrogen to the estrogen receptor (ER) in some way, although aromatisation of testosterone may occur, its effects would be limited due to the inability of the estrogen to bind to the estrogen receptor. Thus through this mechanism, the effects of excess estrogen production through aromatisation would also be limited by use of this steroid.