Background: There is a hypothesis that low socioeconomic status (SES) may explain the link between cannabis use and poorer academic performance and mental health. A key question, therefore, is whether adolescent cannabis use is associated with poorer academic performance and mental health in high SES communities where there is reduced potential for confounding.
Methods: Youth (n=254) from an upper middle class community were followed prospectively through the four years of high school (from age 14/15 to age 17/18). Past-year frequency of cannabis use was assessed annually. Official school records of academic performance and self-reported mental health symptoms (externalizing and internalizing symptoms) were assessed in grades 9 and 12.
Results: Persistent cannabis use across the four years of high school was associated with lower grade-point average (β=-0.18, p=.006), lower Scholastic Aptitude Test (SAT) score (β=-0.13, p=.038), and greater externalizing symptoms (β=0.29, p<.001) in 12th grade, but not with greater internalizing symptoms (β=0.04, p=.53). Moreover, persistent cannabis use was associated with lower grade-point average (β=-0.13, p=.014) and greater externalizing symptoms (β=0.24, p=.002) in 12th grade, even after controlling for 9th grade levels of these outcomes. Similar associations were observed for persistent alcohol and tobacco use. Effects for persistent cannabis use became non-significant after controlling for persistent alcohol and tobacco use, reflecting the difficulties of disentangling effects of cannabis from effects of alcohol and tobacco.
Conclusions: Low SES cannot fully explain associations between cannabis use and poorer academic performance and mental health.
Keywords: Adolescent; Cannabis; Grade-point average; Longitudinal; Mental health; SES.
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