Kimmage is correct when he talks about "grey areas" and athletes always looking for "legal" PEDs. Every well known PED - EPO, HGH, all steroids etc, etc, - have legitimate medical uses. They were not deveolped to aid sporting performance. But coaches, sports scientists, managers/agents search through medical journals where new drugs are peer reviewed to see if anything new is coming onto the market which could have applications to sport. If some new drug is found it will be used, and its use become widespread, because there will be a window of several years before WADA gets round to banning the drug. You can bet your life savings that the search for a replacement for Meldonium has already begun, probably began before it was banned, as soon as whispers were heard saying it might be.
For the great majority of elite performers in all sports there are no "grey areas" or "morally doubtful actions" ; if it ain't specifically forbidden it's legal and they will use it!