The active compound in M-13 is 13-ethyl-3-methoxy-gona-2,5(10)-diene-17-one. This is one of the lesser known structures out there, but it is certainly worth discussing. It is legal because it is a progestin, and before anyone thinks "birth-control", remember that trenbolone, nandrolone, methyltrienolone and Methyl-Dien are all progestins. I doubt anyone will dispute the effects of these compounds upon favorable body composition.

Bottom line, this compound is pretty good in its own right although I think it really works well in a stack, particularly a bulking stack as the gains are somewhat wet.  Remember, wet gains are not necessarily the enemy because you will usually get bigger during the cycle conditioning your body to carry more helping you to eventually carry more lean muscle.  Furthermore, wetter gains typically translate to good strength and well hydrated muscle cells and joints during cycle.

13-ethyl-3-methoxygona-2,5(10)-diene-17-one = 25mg each cap