Often if you can make it past the first interview you don’t get caught unless a workers comp claim gets filed. The place I work we had people * in training* come in smelling like weed, a few others smelling like booze, and one came in very obviously high on coke. From what I remember the only one who got fired was for cursing someone out. Even past that, we’ve had a couple of members of leaderships who were alcoholics who regularly drank on the job, and there was always at least one person smoking in the parking lot.

All depends on employee tolerance and employer need, really.