i have found that underneath the addiction usually lies a codependent issue. you may notice that once the alcoholic gets some sobriety under his belt, if he is working a program he will end up over here, because he has finally reached some clarity to really address the issues that caused him to compulsively reach for a self medication in the first place. i think that is how it is such a vicious cycle because of the way each addict/codie feeds off the other. one feeding the other's addiction.
healthy vs functional, lots of ways we can function around our behaviors, but how healthy is it? does that depend on what our needs are at the time? sorry to go into a circular rant, but this is what the question of addiction and codependency have led me to many many times.