One of the most significant predictors of substance use during adolescence is the proportion of substance using peers. My research project primarily focuses on a social plasticity model of substance use and addiction. We hypothesize that social context serves as a risk factor for substance use engagement during adolescence. At the same time, we also hypothesize social context to serve as a protective factor during (early) adulthood. To study this phenomenon, I combine neuroimaging (fMRI) with behavioral methods to create a better understanding of the social cognitive aspects of heavy cannabis and alcohol consumption. I will primarily focus on the effects of age-related differences in brain activity, structure, and connectivity.