There was a study recently which found that men who used pot
regularly during their adolescent years were twice as likely to develop
testicular cancer.  Most of the time, when teens start abusing marijuana, they know little about the health risks that are associated, and new information is always being discovered.  Compared to other addictive substances such as alcohol, marijuana is considered benign.  But with new information such as higher cancer risk, then maybe this health issue will be enough to persuade teens to stay away from marijuana. 

I've tried to get through to my brother many times regarding his marijuana use.  It seems at that age, teens are set in their ways and remain convinced that there are no health risks associated with smoking pot.  But hopefully if this information is advertised and widely accepted, then it might have a positive effect.