Huffington Post (typically, a fairly mediocre news site) happens to have an excellent article on addiction arguing that the leading cause of addiction is actually social isolation. The original article's long, but I leave you the following excerpt that discusses a policy experiment conducted in Portugal:
There is an alternative. You can build a system that is designed to help drug addicts to reconnect with the world -- and so leave behind their addictions. This isn't theoretical. It is happening. I have seen it. Nearly fifteen years ago, Portugal had one of the worst drug problems in Europe, with 1 percent of the population addicted to heroin. They had tried a drug war, and the problem just kept getting worse. So they decided to do something radically different. They resolved to decriminalize all drugs, and transfer all the money they used to spend on arresting and jailing drug addicts, and spend it instead on reconnecting them -- to their own feelings, and to the wider society. The most crucial step is to get them secure housing, and subsidized jobs so they have a purpose in life, and something to get out of bed for. I watched as they are helped, in warm and welcoming clinics, to learn how to reconnect with their feelings, after years of trauma and stunning them into silence with drugs.