How Teens Thoughts and Behaviors are a Contributing Factor:

Peer pressure. A huge issue in our society today is that of teens having their friends try substances such as a cigarette, then offering it to the entire group. Of course you're not going to say no if all of your buddies are trying it to, and it seems pretty harmless from the outside anyway.
The thought of rejection from those around you is a crippling one, leading teens to do not only what is offered, but going to the extremes just to gain the approval of their peers is what is thought they need these days to fit in.
Perhaps if all children, not just the ones who are pressured into doing these actions, were shown visions and actual stories of people who have done the same thing, and the tragedies that happen due to their misuse of these substances, they'd learn that you should never do them under any circumstance. Even if it means you may be 'in' with certain people. In the long run, it's not worth it.