I think there are subtle physiological differences in people who become addicted.  Sometimes the differences are there at birth, sometimes they result from trauma that maybe affects brain chemistry.  So many times, people with substance abuse problems describe not feeling right or good without their substance.  There's something missing.  Of course, if you take a harmful drug for a while (like meth or crack), it can create permanent furrows in your brain that make it practically impossible to feel right or good.  Some people in that boat have been helped with antidepressants.

I wouldn't be surprised to learn that people who take Ambien, for example, have been able to cut back on the alcohol consumption because the reason for drinking was to eventually fall asleep.  Lots of "self-medicating" going on, much of it socially-sanctioned.

BTW, neurofeedback has been demonstrated to be effective for alcoholics who want to quit.