Recreational marijuana use was legalized in Washington state in 2012. A new study explored the relationship between legalization and marijuana use among students at Washington State University (WSU). Cross-sectional data on self-reported marijuana and other substance use were collected from the National College Health Assessment (NCHA), which was administered at WSU in seven different years, with a mean of 2,069 students surveyed per year. The sample was representative of the WSU undergraduate population, except for an oversampling of White and Asian students. Participants were randomly selected from all survey years except for 2012 and 2014; in these years, survey invitations were sent to all WSU undergraduates. To compare changes in reported past-month marijuana use before and after recreational marijuana legalization, the authors compared WSU data to NCHA national data and the National Survey on Drug Use and Health (NSDUH). (Note: Both of these data sets were ‘contaminated’ with data from students in Washington and Colorado, where recreational marijuana was legalized.) The authors used logit regression to estimate the probability of a student choosing to use a substance and used ordinary least squares regression to estimate the number of days a student used marijuana, controlling for age, sex, race, and year in school. After controlling for a small, predicted increase in marijuana use each year, results of the analysis indicated marijuana use among WSU students increased between 2.0 and 3.5 percentage points each year after legalization and remained higher through 2015. The authors found no evidence legal sales had an additional impact on the proportion of marijuana users. Other findings included a decreasing likelihood of marijuana use after age 20, greater likelihood of use among first-year and Greek students, and positive correlations between marijuana use and other drug use. There were no observed differences in increases in use between underage students and those who could legally purchase marijuana. Use rates among Black and Hispanic students and female students increased the most following legalization. Frequency of marijuana use increased by a small, but significant, number of days per month following legalization, but no significant changes were observed following legal sales. Using difference-in-difference comparisons to national data, the authors estimated the effect of legalization was an increase of 8.6 percentage points (NCHA) to 9.6 percentage points (NSDUH) in likelihood of using marijuana.

Take away: Following legalization of recreational marijuana in Washington state, probability of marijuana use and frequency of marijuana use increased among Washington State University undergraduates. Black and Hispanic students and female students had the largest increases in probability of use.

Citation: Miller AM, Rosenman R & Cowan BW. (2017). Recreational marijuana legalization and college student use: Early evidence [published online ahead of print August 03 2017], SSM – Population Health doi: 10.1016/j.ssmph.2017.08.001