Modes of Marijuana Consumption Among Colorado High School Students Before and After the Initiation of Retail Marijuana Sales for Adults.

Objective: This study aimed to estimate the prevalence of different modes of marijuana consumption (e.g., smoking, ingesting) overall and by sociodemographic factors, marijuana-related perceptions, and other substance use among adolescents, as well as to characterize differences in the usual mode of consumption before and after the initiation of retail marijuana sales in 2014.

Method: Data are from the 2013 and 2015 administrations of the Healthy Kids Colorado Survey, a cross-sectional, school-based survey. We included 9th-12th grade students who reported past-30-day marijuana use in 2013 (n = 2,792; 44.8% female) or 2015 (n = 1,664; 48.9% female). We estimated the prevalence of any past-month use of each mode in 2015 and usual mode of consumption the past month in both years. We tested differences by year, sociodemographics, marijuana-related perceptions, and other substance use using Rao-Scott chi-square tests and multivariable logistic regression.

Results: The prevalence of past-month marijuana use was 20.7% in both years. In 2015, 39.8% of students reported using multiple modes in the past month. Use of any mode other than smoking and use of multiple modes differed by sociodemographics, marijuana-related perceptions, and other substance use. Smoking remained the most common usual mode in 2015. The prevalence of usually ingesting significantly decreased from 4.7% to 2.1% between years, whereas "other mode(s)" significantly increased from 4.0% to 6.0%.

Conclusions: The use of multiple modes of marijuana consumption was prevalent among adolescents in Colorado. The usual mode of consumption changed in years before and after the implementation of retail marijuana sales, suggesting the need for continued surveillance.