There have been some cases raised by patients/families in the care of drug addicts but largely the problem goes unnoticed.
When I went to the hospital for my dad's heart surgery, I wandered to one area and found the outdoor gather place where doctors and nurse (and other largely medical staff) smoked cigarettes. No crime in that, just that one would think that they would see enough sick people to put them off that habit.
Cigarettes don't notably affect job performance although the case could be made that Xanex and other prescription meds (used by medical staff) do.
Rush was not operating heavy machinery sitting at a table behind a microphone either. Ed McMahon may have gone on the Tonight Show bombed on drinks at times but did it really affect his performance? A number of people seem to "fondly" recall those nights. If you are the captain of a boat, have a few too many, and let someone else command the ship, you are liable to get some flack about it (even if you weren't behind the wheel).