I used to think that an addict was somebody who lacked moral strength. Others argue that addicts suffer from a chemical dependency or a mental disorder.
In his book God of Our Understanding: Jewish Spirituality and Recovery from Addiction, Rabbi Shais Taub writes:
All human beings have a deep-seated need for spiritual contact. But most people can also live their lives without it. Addicts are people who, for whatever reason, are unsettled to the core and cannot handle the business of life without maintaining a continual and acute awareness of the Divine. Absent such higher consciousness, they are miserable and sick. What makes their dilemma fatal is that their drug of choice will actually produce in them short-term affects that simulate the release and relief that can only really be had through spiritual consciousness. Consequently, the only real treatment for their condition is to make sure that they get the “real thing” instead of self-medicating with the fake stuff, for if they do not get the real thing, they have no choice but to take the fake stuff.