Health information that is acquired through information scanning has been shown to play an important role in shaping individual beliefs and health behavior. This study examines the direct and indirect effects of the breadth of scanning from media and interpersonal sources about two risk behaviors (nonmedical use of amphetamines and marijuana) on subsequent drug use behavior through changes to perceived norms. We test effects of scanning using a longitudinal online survey design with data collected at six-month intervals over three time points among 800 Israeli undergraduate students in their freshman year. Of the 800 respondents who participated in the first wave, 62.4% completed the second wave (N = 499), among which 347 (69.5%) completed a follow-up 6 months later. Results of cross-lagged structural equation models find that scanning information about amphetamines from interpersonal sources at 6 months predicted an increased likelihood of nonmedical use of amphetamines at 12-months. In addition, young adults who scanned information about marijuana from media sources at 6 months reported greater nonmedical marijuana use at 12 months. Breadth of scanning about marijuana from media sources mediated the relationship between perceived norms and marijuana use at 12 months. Results also showed indirect effects of scanning at baseline on nonmedical drug use at 12 months through scanning from the same source at 6 months. These findings contribute to our understanding of the role of information scanning and perceived norms in shaping substance use behaviors, and suggest that scanning may serve as a potential early indicator of risk.