Captain America isn't as cost-less as you think; to quote from the Marvel Wikia about the 'super-soldier serum' that makes a Captain America:
But the more powerful variants come with strange side-effects that may also include mental deficiencies.
(In one random comic - I have no idea which - that I read as a kid, S.H.I.E.L.D. had apparently put Captain America into cryogenic suspension specifically to stop the serum from killing the cap'n, in the hopes that the future could fix him. Quite a side-effect.)
Limitless is a movie coming out this Friday which includes nootropics as a major plot device. I think that the way they are portrayed in the movie, and the subsequent media discussion (if any) about nootropics would be of interest here, even if the movie isn't.
From what I can tell, the movie is about a guy who uses a drug to improve his mental capabilities, uses those to radically alter his life, who is then targeted because its just that genre of movie.
Just a heads up, if anyone is interested.