That's kinda like putting current political figures in your games. On the one hand, it might just be what's needed to have the game make sense. For example, if you have President Bush in your dream-themed game be indestructible and your goal is merely to survive and escape to the next level, I would think that's a lot more acceptable than having him be a boss in your game. But then, this goes into one of those 'how far do you want to push it' kind of deals, because either way, you're going to get some sort of flack over including it in the game.
Take Deus Ex, for example. Their 'drug' of choice was Zyme, but you never saw the powder. You only saw the vials it was contained in. The game still contained the drug element, and it incorporated the drug into a few of the tasks in the game, but at the same time, it was done in a tasteful manner.
Still, I agree with Van, if you're going to do the drugs thing, at least have a disclaimer saying what your game has and that you do not promote the actions within the game.
Gemstone Games is now Cornett Media