Reduced motivation is often noted as a consequence of cannabis use. However, previous work has yielded mixed results and focused largely on adults. To address these limitations, this study examined longitudinal associations between cannabis use and self-reported motivation in a large adolescent sample.

Participants were 401 adolescents aged 14–17 at baseline who completed five bi-annual assessments. We assessed motivation at three timepoints using two self-report questionnaires: the Apathy Evaluation Scale and the Motivation and Engagement Scale (disengagement, persistence, planning, self-efficacy, and valuing school subscales). Controlling for relevant covariates, we used latent growth curve modeling to characterize patterns of cannabis use and motivation over time, examining bidirectional influences between these processes.

On average, adolescent cannabis use frequency increased significantly over time. The disengagement and planning facets of motivation also increased significantly over time, whereas other aspects of motivation remained stable. At baseline, greater cannabis use was associated with greater disengagement, lower planning, and lower valuing of school. Greater baseline cannabis use also predicted lesser increases in disengagement over time. After controlling for the effect of sex, age, depression, and use of alcohol and nicotine, only the baseline association between cannabis use and valuing school remained significant.

Our results do not support a prospective link between cannabis use and reduced motivation among adolescents. Although most observed associations were accounted for by covariates, greater cannabis use was cross-sectionally associated with lower perceived value of school, which may contribute to poorer educational and later life outcomes.