Just retexture a Zombie and you should be okay for a druggie on downers.
If you want him hopped up on something then just make him faster.
Edit
Don't forget to make the T-Shirt say "where's my pills?" in the re-texture.

Or maybe it could say, "Just say Yes to drugs".
Their would be no confusion on the players part about them being a drugie on the second one.
But then again, it's not the best message to be displaying, so the first one is probably better, which could be perceived as prescription drugs or illegal narcotics.
But then again, I guess the second message could be perceived either way as well.
Yeaah, yeah, you could do "Just say Yes to drugs" on the front of the shirt and then on the back say..."pharmacists need jobs too”