Nowadays, talking with family or friends, everyone seems to have a family member who is/was addicted to some substance or behaviour and how it affects/affected the entire family. I've been doing a bit of research on it trying to understand. Here is an interesting link to an article I found:

Addiction is a Brain Disease : The Addiction Recovery Guide

A core concept evolving with scientific advances over the past decade is that drug addiction is a brain disease that develops over time as a result of the initially voluntary behavior of using drugs. (Drugs include alcohol.)