Here is a site I came across that might be helpful:
http://www.talkingwithkids.org/drugs.html
Also, I highly recommend the show Intervention on A&E (if you have On Demand, you can watch these anytime). The show is a half hour long, usually follows one or two people addicted to something, the effects it has on the family and the intervention.
I agree with Jenny's post, you should always talk with your child about drugs, don't just have one sit down or put him in front of videos. Keep the lines open when it comes to this. From my own personal experience. My parents NEVER talked to me about sex, smoking, drinking or drugs and I experimented with them all. I NEVER felt at the time that I was hurting my body and I never ever thought about consequences. Lucky for me, I didn't stay on them or get pregnant at a young age. For me, I just grew out of it but not everyone is that lucky. Talk to your kids, I know I will!
M.