Mechanics for drug addiction:
Each time a drug with an Addiction level wears off there is a percent chance of the slave becoming drug addicted. This chance is the total of all addiction levels of all drugs taken.
Each day a slave is drug addicted they take negative stat effects and the addiction level decreases 10. When it reaches 0 then they are no longer addicted.
So far only the Drug Dealer's drug seem to have an Addiction level.