Effect of the COVID-19 pandemic on adolescent mental health and substance use up to March, 2022, in Iceland: a repeated, cross-sectional, population-based study

BACKGROUND: Poor mental health in the first year of the COVID-19 pandemic has been well documented in adolescents; however, less is known about the longer-term effect of the pandemic. We aimed to examine adolescent mental health and substance use as well as covariates associated with these outcomes 1 year or more into the pandemic. METHODS: A nationwide sample of adolescents aged 13–18 years enrolled in school in Iceland were invited to complete surveys administered during October–November or February–March, 2018, October–November, 2020, February–March or October–November, 2021, and February–March 2022. The survey was in Icelandic for all administrations and offered to adolescents aged 13–15 years in English in 2020 and 2022 and in Polish in 2022. Surveys assessed depressive symptoms (Symptom Checklist-90); mental wellbeing (Short Warwick Edinburgh Mental Wellbeing Scale); and the frequency of cigarette smoking, e-cigarette use, and alcohol intoxication. Covariates comprised age, gender, and migration status as determined by language spoken at home, level of social restrictions based on residency, parental social support, and sleep duration (≥8 h nightly). Weighted mixed-effect models were used to determine the effect of time and the covariates on mental health and substance use. The main outcomes were assessed in all participants with more than 80% of the necessary data, and multiple imputation was used to handle missing data. Bonferroni corrections were used to adjust for multiple testing and analyses were considered significant at a p value of <0·0017. FINDINGS: 64 071 responses were submitted and analysed between 2018 and 2022. Elevated depressive symptoms and worsened mental wellbeing across girls and boys aged 13–18 years were observed to have been maintained up to 2 years into the pandemic (p>0·0017). Alcohol intoxication initially decreased during the pandemic but increased again as social restrictions eased (p<0·0001). No changes were observed in cigarette smoking and e-cigarette use during the COVID-19 pandemic. Higher levels of parental social support and an average sleep duration of 8 h or more per night were associated with mental health better outcomes and less substance use (p<0·0001). Social restrictions and migration background were inconsistently associated with the outcomes. INTERPRETATION: Population-level prevention targeting adolescent depressive symptoms should be prioritised in health policy in the wake of COVID-19. FUNDING: Icelandic Research Fund.