Long time reader Mary sent me details of a study on how legal and illegal drugs effect the developing brain. The results suggest that Delta FosB, a brain chemical that is linked to addiction, greatly increases. However this only happens in adolescent brains, not in young or older brains. This highlights both how adolescent brains far more plastic and subject to change than adult or child brains.
See Jefferson Scientists Find Evidence Of Greater Sensitivity To Addictive Drugs In Adolescence for a write up of the study or Periadolescent Mice Show Enhanced Delta FosB Upregulation in Response to Cocaine and Amphetamine for the original study.