Sure, they may say “controlled substance,” but a lot of the stuff hitting the streets in the future came from somewhere, and probably with some bad intentions. Nor does your drug fix necessarily come from some shadowy character on the street or in the clubs....he could easily be the face behind the counter who's happy you're back for your monthly doses.
With all the medical advances the future has to offer, there is a market in need of tapping (much like the veins on a junkie) for performance enhancers, stimulants and boosters to enhance day to day life. Sure, there's always some setbacks involved....and in some cases, these enhancers might actually be worst than the contraband of today. But, as long as the pharmacorps are paying the politicians to look the other way, there's some business to be made.
Disclaimer: As stated before, this is a bit of a mature game that romanticizes some things that, in real life, is actually a really bad deal. If you're not comfortable with drug use in your game, then don't use it. And if you're not comfortable with the ethos of this game, don't play it. The cyberpunk genre doesn't have its black and white, it has its varying shades of gray. It's where authorities are villains, and the outlaws are champions.