• Andrew L Koval, KerrDavid C RDCRb School of Psychological Science , Oregon State University , Corvallis , USA., and Harold Bae.
• a School of Biological and Population Health Sciences, College of Public Health and Human Sciences , Oregon State University , Corvallis , USA.
• Am J Drug Alcohol Abuse. 2019 Jan 1; 45 (4): 392-399.

AbstractBackground: Oregon students' rates of marijuana use have increased following recreational marijuana legalization (RML), but the relation between RML and students' perceived peer use of marijuana - or descriptive norms - is unknown. Objectives: This study examined whether perceived peer use of marijuana changed more following RML for college students in Oregon than in states without RML. Methods: Repeated cross-sectional data were collected from the National College Health Assessment-II surveys from 2008 to 2016 to assess changes in descriptive norms ("Within the last 30 days, what percent of students at your school used marijuana?") among 18-26 year-old undergraduates from two Oregon institutions and 123 institutions in non-RML states (N = 280,006; 66.23% female; 33.19% male) following Oregon RML (7/1/2015). Mixed-effects regressions were used to account for clustering at the institutional level; models controlled for covariates and secular changes in descriptive norms. Results: RML was associated with higher perceived rates of marijuana use by peers [Percent Increase = 3.09, p < .001]. The effect was significant for respondents who had never used marijuana [Percent Increase = 3.72, p < .001], but not for respondents who recently or ever previously used marijuana. Respondents who had recently used marijuana had higher descriptive norms than those who had never used [Percent Increase = 12.83, p < .001]. Conclusions: Given the association between descriptive norms and personal use, RML-related increases in descriptive norms among non-using students could contribute to future marijuana use initiation and may be one mechanism linking RML with higher rates of marijuana use among college students.

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