I will admit to being curious about some designer drugs like Vicadin. Although arguably, even though OTC aspirins are legal, I don't use them at all - Even when I have a headache.
Seriously though, the expense and to a certain degree - the illegality is a deterrent. I'd much rather spend $50 on a good videogame than go on a one night bender on drug of choice. I guess it comes down to what a person enjoys more and what they are willing to spend their time and effort on.