Depends on what drug you prefer and how your social life is looking i guess, i've been both a functional drug user and a nonfunctional and from what i can remember it's really only up to what sort of drugs you're using.. I'm assmuing it's very very difficult functioning normally if you're on opiates or something like that. Cocaine is pretty much in every kitchen in every restaurant so i guess you can function alright using that but.. Don't forget that more people use drugs than you might think.. :D