Abstract Background Preclinical and human studies suggest that adolescent cannabis use may be associated with worse cognitive outcomes than adult cannabis use. We investigated the associations between chronic cannabis use and cognitive function in adolescent and adult cannabis users and controls. We hypothesised user-status would be negatively associated with cognitive function and this relationship would be stronger in adolescents than adults. Methods As part of the ‘CannTeen’ project, this cross-sectional study assessed cognitive performance in adolescent cannabis users (n = 76; 16–17-year-olds), adolescent controls (n = 63), adult cannabis users (n = 71; 26–29-year-olds) and adult controls (n = 64). Users used cannabis 1–7 days/week. Adolescent and adult cannabis users were matched...