You're saying the root of all substance addictions is low self-esteem?
It's a big, big part of it. I have never met an addict or alcoholic who didn't have very low self-esteem. Not once. And I have met hundreds, if not thousands. It seems to be a pervasive theme among all addicts and alcoholics. that said, I never use "global" terminology and I would never say that the root of ALL substance addictions is ALWAYS low self esteem. There are always exceptions. And anyone who has taken a freshman-level course in stats knows that correlation does not equal causality.
But from what I have seen, low self esteem goes hand-in-hand with addictive behaviors, especially when talking about drugs, alcohol, and sex. Probably other addictive behaviors as well (eating disorders, compulsive spending, for example), but I'm not going to go into those, though the people I know who have had eating disorders or who were compulsive spenders also had really low self-esteem. Karen Carpenter is one public example (eating disorder) and my ex-wife is another (compulsive spender which, when the funds got cut off during the divorce process, turned into a sex disorder resulting in her getting the herp).