The Realities of Addiction

I live a very clean life, but in my extended family, we have a lot of problems with drugs and alcohol. I feel very lucky to have been raised the way I was and to be free of those sorts of problems. But this also makes it difficult for me to understand why people like my relatives would do the things they do, or how they could allow themselves to fall into such terrible habits.

What can the experts tell me about addiction that might make me a little more open-minded, and help me be more loving and understanding toward those struggling with addiction?