Years ago, before I went to treatment for the first time, my wife was worried about my drinking and whatnot and asked that I get a physical and tell the doctor honestly to see what he said about my drinking. FYI - at the time I was drinking roughly a liter of gin a night.
Doctor asks me how many drinking I'm having per day. I told him approximately 20 drinks per day. (I'm not sure if 20 oz. = one liter or not - but I thought I was being honest at the time.
He asked if I was having trouble holding a job, getting any DWIs, trouble at home, etc. I told him no there was no trouble with any of that stuff. And he said some people can handle that much liquor. The only concern was the liver and that would be checked with part of the physical.
Basically, his point was that if I'm not having any consequences, there must not be a problem.
My point is that much of the medical profession has no clue about drug/alcohol abuse. That's why it's best (in my experience) to work with health care professionals who have experience/training in substance abuse.
In addition, if I'm not honest with my doctors about what I'm putting in my body, they aren't going to know. They may suspect or see signs, but that's neither here nor there.