Trajectories of marijuana use in youth ages 15-25: implications for postsecondary education experiences

Abstract

Objective: This study examined associations between longitudinal trajectories of marijuana use from adolescence to young adulthood and postsecondary education (PSE) experiences. Outcomes examined included the type of PSE undertaken, the timing of enrollment, and the likelihood of dropping out.

Method: Participants (N = 632; 332 females) were from the Victoria Healthy Youth Survey, a five-wave multicohort study of young people interviewed biennially between 2003 and 2011. Latent class growth analysis was used to identify distinct trajectories of the frequency of marijuana use from ages 15 to 25. Logistic regression analyses evaluated class membership as a predictor of the three PSE outcomes, with sex, maternal education, family structure, high school grades, and conduct problems controlled for.

Results: Three trajectory groups of marijuana use were identified: abstainers (31%), occasional users (44%), and frequent users (25%). Compared with abstainers, frequent users had the lowest high school grades and the most conduct problems and were least likely to enroll in PSE, especially in a university. Occasional users did not differ from abstainers on high school grades or conduct problems and were no less likely than abstainers to enroll in PSE. However, they delayed enrollment longer and were more likely to drop out of PSE.

Conclusions: Frequent marijuana use from adolescence to young adulthood may close off opportunities for entering PSE, whereas occasional use may create delays in starting and finishing PSE among less at-risk young people. The mechanisms underlying associations between marijuana use and educational difficulties during emerging adulthood as well as adolescence need to be better understood.

Figure 1

Predicted marijuana use trajectories from ages 15 to 25 for abstainers, occasional users, and frequent users. Because the log-odds trajectories are on arbitrary scales, the estimated thresholds that divide the categories of observed data are shown as dashed lines to facilitate interpretation. The first (lowest) line represents using marijuana a few times a year, the second a few times a month, the third a few times a week, and the fourth more than once a week.