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Substance use has been associated with blunted brain responses to non-drug rewards, but findings in people who use cannabis are mixed. Adolescents may be uniquely vulnerable to cannabis-related disruption to reward processing due to ongoing neuromaturation, but longitudinal research is lacking. In this longitudinal fMRI study, we compared brain measures of reward anticipation in 46 adolescents (16-17 years) and adults (26-29 years) who used cannabis (1-7 days/week) and 50 age-matched controls with the Monetary Incentive Delay task at baseline and 12-month follow-up. Region of interest (ROI) analyses adjusted for cigarette/roll-up use, depression, and risk-taking found that reward anticipation activity decreased in the right (p = 0.05, η_p² = 0.04) and left (p = 0.02, η_p² = 0.05) ventral striatum from baseline to follow-up in participants who used cannabis compared with control participants. These effects remained in unadjusted models and when including only participants who consistently used or abstained from cannabis during the study period. There were no significant interactions between the cannabis user-group and age-group, or between the user-group, age-group, and time. There were also no cannabis user-group main or interaction effects in full sample ROI analyses for the thalamus, insula, or supplementary motor area, or in exploratory whole-brain analyses. The current results suggest that cannabis use may be associated with reductions in non-drug reward anticipation activity in the ventral striatum, a key part of the brain's reward system. However, there was no evidence of adolescent resilience or vulnerability to cannabis-related changes in brain reward anticipation activity.