[otakucode]

You made a good point that I just wanted to make explicit, because I think it is generally not something people know or at least not something they've thought much about - The FDA has a very specific mandate. They regulate any substance which "treats, prevents, or cures any disease." They specifically do not regulate, or test for, any substance which would claim to improve the functioning of a healthy person. If a drug came out tomorrow which would enable you to lift 50 kilos more tomorrow than you can life today, the FDA would have no jurisdiction over it (unless someone wanted to give it to patients suffering from muscular impairment due to a disease, of course). This is also one of the reasons why the FDA does not regulate alcohol and cigarettes. Those substances are not meant to treat, cure, or prevent anything.

I'm not clear on whether such a 'strengthening' drug would be legal to sell, just that the FDA could not authorize it for sale.

[danneu]

That's not true.

What you defined is a drug.

    Accordingly, these ·products are drugs, under 
    section 201(g)(1)(C) of the Act, 21 U.S.C. § 321(g)(1)(C),
    because they are not foods and they are intended to affect
    the structure or any function of the body. Moreover, these 
    products are new drugs as defined by section 201(p) of the 
    Act, 21 U.S.C. § 321(p), because they are not generally
    recognized as safe and effective for use under the 
    conditions prescribed, recommended, or suggested in
    their labeling.

And you bet the FDA cares.

    Under sections 301(d) and 505(a) of the Act, 
    21 U.S.C. § 331(d) and 355(a), a new drug may not
    be introduced or delivered for introduction into 
    interstate commerce unless an FDA approved application 
    is in effect for it.

[ekianjo]

Completely false. Be it for the potential side effects of such a substance, it would be considered as a drug anyway since it would require proper medical monitoring. Even cosmetics are sometimes at the borderline of drugs based on the claims they make and the effects they have.

The reason why alcohol and cigarettes are not regulated as drugs is rather based on historical, political and economical factors. They have existed for a long time and people are considered responsible enough to know how not to abuse them, they have a well known risk factor, and they bring back lots of tax money to society when authorized.

But for any new substance, you bet FDA would be involved, no matter whether you call it a drug or not.