Er, there were millions of high functioning meth users (was common in quite a few industries because it was available at convenience stores, and wasn't just truckers although it was definitely popular in that industry), and it was prevalent in diet pills as well.
I wrote something about how I remembered this article (but I got info wrong after rereading it) so this is more worth it:
A Columbia University psychiatry professor talks about what he's learned from trying the drug himself and studying it over the years.
www.vice.com
Like every other fucking drug out there, people have a pretty shitty view of it based on moronic nonsensical abstinence only shit. Which I'm not advocating for drug use, but the anti-drug shit is very often very wrong, often in astoundingly stupid ways.
Which isn't to say Maher isn't a clown. He is. But not sure why you think there aren't tons of high functioning drug users of all types. If you knew the truth of how much shit people are on you'd probably lose your mind. Hell I know some people that are such ridiculous caffeine users that the amount of caffeine they use daily probably ends up with comparable effects to regular habitual users of cocaine or meth.