The Impact of Marijuana Use Trajectories on College Student Outcomes

Introduction:  Many studies have established links between marijuana use and academic performance in college.  However, little is known about the impact of marijuana trajectories during college on college outcomes.  This study identifies marijuana use trajectories over the college career and explores the relationships between these trajectories and enrollment, intention to graduate on time, graduate school aspirations, and college grade point average.

Methods:  We used data from a longitudinal study of 3,146 undergraduate students from 11 colleges in North Carolina and Virginia.  At six time points over their college career, students reported how many days in the past month they had used marijuana.  Group based trajectory modeling identified the most common patterns of marijuana use over time.  Random-effects linear and logistic regression models were constructed in order to explore associations between marijuana use trajectories and college outcomes measured during the students’ senior year of college.  Models were adjusted for gender, race, ethnicity, mother’s education, and spending money when these characteristics had a marginal bivariate association (p < 0.20) with the outcomes.

Results:  Five marijuana use trajectories during college were identified: non-use, infrequent use, decreasing use, increasing use, and frequent use. Non-users were more likely to stay enrolled in college than frequent marijuana users (AOR=2.1; 95% CI=1.1, 4.0).  Non-users were more likely to plan to graduate on time than infrequent users (AOR=1.4; CI=1.1, 1.8), decreasing users (AOR=1.8; CI=1.1, 2.9), increasing users (AOR=1.7; CI=1.1, 2.8), and frequent users (AOR=2.1; CI=1.2, 3.9).  Non-users (AOR=1.7; CI=1.0, 2.7) and frequent marijuana users (AOR=2.3; CI=1.2, 4.2) were more likely to plan to attend graduate school after graduation than increasing marijuana users.  Non-users, on average, earned grade point averages that were 0.11 points higher than infrequent users, 0.21 points higher than decreasing users, 0.31 points higher than increasing users, and 0.24 points higher than frequent users (p < 0.05).  Infrequent marijuana users, on average, earned grade point averages that were 0.20 points higher than increasing users and 0.13 points higher than frequent users (p < 0.05).

Conclusion:  Some marijuana use patterns over time are associated with poorer college outcomes.  These findings have important implications for substance abuse prevention efforts on college campuses.

Financial Support:  This research was supported by Award Number R01CA141643 from the National Cancer Institute.