The drug policies of the major and minor leagues are not 100% duplicative,me either in the drugs tested for, nor the suspensions laid down. For instance, players on the 40 man roster are subject to the ML policy and thus are not subjected to tests for marijuana - just last year there was an unnamed minor leaguer that got busted for pot and was quoted as saying "I'll just smoke my way to the 40 man".
Here is the list of banned substances
https://en.m.wikipedia.org/wiki/List_of_banned_substances_in_baseball. You will notice oxilophrine listed under the stimulants section, which is where the two drugs that make up Adderall are also listed.
You can then look at the lists of minor league suspensions the last two years here
http://www.baseballamerica.com/minors/minor-league-drug-suspensions-2015/ and here
http://www.baseballamerica.com/minors/minor-league-drug-suspensions-2014/. You will notice that the stimulant suspensions in the minor leagues are always 50 games, not 25 like Davis got. It is considered nothing more than a greenie.
Anything anabolic, hence muscle building, is listed under steroids. You'll notice on the minor league lists that steroid suspensions are at least 72 games if not more.
Oxilophrine is not, in any way shape or form, an end around on steroid use nor should it be looked at as an attempt to build muscle mass any more than Red Bull should.