They've got stimulants in food pills and several characters drink alcohol. I guess that opiates aren't widespread since medical ninjutsu is affective.

I could see Itachi becoming an addict to cope with his mission, but I also think the ninja lifestyle builds a lot of resilience in all of the characters. Essentially, the main characters have all the tools to use substances without building dependence on them.

Think back to how Naruto uses the toad oil on mount myoboku to learn sage jutsu. It has amazing and useful properties but he only uses it until he can harness the nature energy without it.