Mesterolone is an old steroid, first developed in the 1960s and introduced for medical use by Schering under their brand name Proviron as early as 1967. The well-established trademark "Pro" had previously been used on testosterone propionate since 1936 when it came out of patent protection from Bayer AG.

Ever since Testosterone and other hormones became a focus for bodybuilders, Mesterolone has been on their minds. The question is whether this will unlock an endless amount of gains without any side effects?

Masteron and Mesterolone are both very similar in structure, with the only difference being that Mesterolone is orally active while the Masteron must be injected. In addition, they're both 1-methylated molecules of dihydrotestosterone (DHT), which means they have a slightly different effect on your body than regular Testosterone does. For instance, Masteron will raise estrogen levels due to its affinity for aromatase enzymes rather than blocking them. However, Testosterone can do so effectively enough without binding too much hemoglobin (as happens when you inject).