My brother is an addict, and his substance of choice is alcohol. He's not a functional alcoholic, but a self-destructive alcoholic.
Eight months ago he relapsed, and it hasn't been pretty. He's now, thankfully, on the road to recovery and as a family we've had a lot of learning to do... because rehabilitation is not just about the person within, it's about the external environment and all the people in it.
During this I have been involved in Al-Anon family support groups, and as a Psychology student I've been doing research on addiction.
I knew I was addicted to sugar, but it wasn't until recently that I realised how similar the addiction process is - the substance may be different, but the attachment and reasons for dependency are the same. We reach to these substances for comfort, and they become our answer in times of stress/angst/happiness/sadness. We find reasons to use them, and before we know it we have a deep emotional attachment to the feelings that our substance of choice brings us.
From a personal point of view, I know that I have to give up chocolate (My name is Luceeloo, I'm a chocolate and sugar addict and I am 8 days clean), but the thought of not eating my beloved cadbury's again... the substance that can cheer up a bad day, or make me feel guilty for having no control... the thought of not having that is something that I am only starting to accept.