OBJECTIVE: Emerging adulthood (18-25 years) is associated with peak prevalence of cannabis use. Although population-based longitudinal studies have found little change in cannabis use among emerging adults during COVID-19, research examining changes among vulnerable subgroups is lacking. The present study examined the association between emotion dysregulation at 23 years and change in cannabis use frequency and problem cannabis use among a large sample of emerging adults, from before to during the COVID-19 pandemic. METHOD: Longitudinal data were analyzed from 1,226 emerging adults (59% female; n = 738 reported cannabis use) who completed online surveys before the pandemic (2019; age 21) and 1 year into COVID-19 (2021; age 23) as part of the Québec Longitudinal Study of Child Development. RESULTS: There was no significant overall within-person change in cannabis use outcomes during COVID-19 among the emerging adult sample. However, emotional clarity (a dimension of emotion dysregulation) at 23 years significantly moderated change in problem cannabis use during COVID-19. Namely, low emotional clarity at 23 years was associated with increased problem cannabis use (B = 0.79, 95% CI [0.23, 1.34]), whereas high emotional clarity at 23 years was associated with decreased problem cannabis use (B = -0.68, 95% CI [-1.27, -0.09]) during COVID-19, among men only. CONCLUSIONS: Findings highlight the need to consider changes in cannabis use during COVID-19 among emerging adults with elevated emotion dysregulation (and particularly, low emotional clarity among men) and reiterate the need for supports and targeted interventions to reduce cannabis use and decrease associated harms as society emerges from COVID-19.< Réduire