The problem is that addictive drugs in these games are not a particularly good model, except, maybe, for speed.
Think, for a moment, how would you model marijuana in an MMORPG? Your character grins more, and is a bit hungrier, but neither significantly physically enhanced or impaired? Would anyone enjoy a virtual joint? RPG drugs have to have both benefits and costs, and things just don't work that way in the real world. Some drugs have no identifiable "benefit" and some have little in the way of cost or harm. Some both, some neither.
The other untidy thing about drug use is that lots of people use drugs, even what you or I would consider outrageously dangerous drugs, without becoming addicts or they are able to quit without treatment.
Then there are the games that try to be too good and didactic, like There.com. Faugh! Paintball, but no guns! What kind of lame drugs would they have?