Substance abuse in anesthesia is a serious issue that needs to be talked about.
The issue is access. Internal medicine residents order morphine on a paper sheet and it is "magically" given to the patient by the nurse, much like your mom used to do your laundry. In the OR, an anesthesiologist who wants to give morphine has to reach into the narc box, draw it up and then push it - huge difference in access.
I think substance abuse is a disease, much like diabetes or hypertension - some people have it, some don't. Some people are just predisposed to abusing alcohol, caffeine, tobacco, etc. People who have this kind of self-awareness and insight should probably look to another career besides anesthesia. A classmate of mine clearly stated that he would never go into anesthesia precisely because of these concerns and I think that was very wise.
Then the other issue is "experimentation". Some people aren't necessarily substance abusers, but have a curiosity as to what something is like. At one of the places I rotated, one resident told me that the attendings sat them down at the start of their residency and said "yes, fenanyl IS that good. don't try it".
Some people (i.e. "experimenters") may be able to come back to anesthesia after rehabilitation. Other people (i.e. "predisposed abusers") may not. Regardless, substance abuse is an occupational hazard much like needle sticks.