According to statistics, half of all american teens will experiment with illegal drugs before they graduate high school

Explanation:

According to American Academy of Child and Adolescent Psychiatry, illegal drugs experimentation during teen ages is common but not normal. This happen because teenagers don't have the ability of seeing the consequences of their actions, they are just emotional people that want to feel and experience about almost every single adult issues like alcohol, drugs, sexual intercourses, and so on.

Moreover, lacking of responsibility, teenagers don't consider all negative affects from drugs. Another reason of this phenomenon is the social pressure. Teen ages are highly social demanding, because during those ages they want to be accepted by their peers, and to achieve it, they often do everything.

i believe the answer would be negative peer pressure