Basically, what has happened is that during the anabolic revolution (the early sixties) pharmaceutical companies were trying all sorts of testosterones out. Some made it to commercial market, others didn't. For example Anadrol did SuperDrol didn't, although both were researched by Syntex labs.
Due to the availability of information, and research chemicals from the east, all that has happened is that people have looked into what was researched in the early 60's, that never made it to commercial market, then compared that with relevant country drug legislation, and if it isn't on the list then they sell it in that country. Simples!
As most of these steroids never got commercially manufactured, they are not on banned drug lists, or POM lists, so technically you can sell them. But trust me, these substances are Anabolic Androgenic Steroids, and mg for mg most of them are stronger and higher in side effects than the real thing. 30mg S-Drol is about the same as 60mg Dbol. 10mg of M1T is about the same as 50mg Anadrol.
In summary, most of today's 'pro-hormones' are just steroids that were trialled years ago, but never made it to manufacture. A ressurection if you like.
