I don't know exactly for what class(es) this would be appropriate besides Rogue and maybe Fighter, but I would like to suggest, for those who are involved in the decisions being made, that a perk based around Addictions be considered. It could be based on number of substances a character is addicted to determining a straight bonus to this or that, or it could be that the penalties for addictions are lessened, or any number of things. However it turns out, I think it would be in line with the EfU tradition of rewarding people who take risks.
Uh... isn't there a thread for this sort of thing already?
Regardless on whether there is or isn't another thread, this seems like a suggestion that takes the risks out of the drugs for those that want to use them. They kind of come with their own perk system which rewards their usage. That is my take on it anyway.