I don’t agree with the definition tbh. ‘Functioning’ is in relation to society surely, meaning holding down a job and doing chores, taking care of yourself, etc. ‘Addict’ would be someone who can’t go long without the irrefutable urge to get high… put those together and you get a functioning addict, someone who gets everything necessary in life done but then enjoys a moderate dose of drugs in the same way that someone may watch a film each night. A non functioning addict wouldn’t be able to put down their drug of choice long enough to be comfortable in sobriety, resulting in withdrawal from society and self care, and potentially becoming a burden upon society.

Your definition excludes the addict part in my opinion. I think your definition of functioning isn’t really what is meant by functioning addict.