Background Adolescence represents a crucial developmental period in shaping mental health trajectories. In this study, we investigated the effect of the COVID-19 pandemic on mental health and substance use during this sensitive developmental stage. MethodsIn this longitudinal, population-based study, surveys were administered to a nationwide sample of 13-18-yearolds in Iceland in October or February in 2016 and 2018, and in October, 2020 (during the COVID-19 pandemic). The surveys assessed depressive symptoms with the Symptom Checklist-90, mental wellbeing with the Short Warwick Edinburgh Mental Wellbeing Scale, and the frequency of cigarette smoking, e-cigarette use, and alcohol intoxication. Demographic data were collected, which included language spoken at home although not ethnicity data. We used mixed effects models to study the effect of gender, age, and survey year on trends in mental health outcomes. Findings 59 701 survey responses were included; response rates ranged from 63% to 86%. An increase in depressive symptoms (β 0•57, 95% CI 0•53 to 0•60) and worsened mental wellbeing (β -0•46, 95% CI -0•49 to -0•42) were observed across all age groups during the pandemic compared with same-aged peers before COVID-19. These outcomes were significantly worse in adolescent girls compared with boys (β 4•16, 95% CI 4•05 to 4•28, and β -1•13, 95% CI -1•23 to -1•03, respectively). Cigarette smoking (OR 2•61, 95% CI 2•59 to 2•66), e-cigarette use (OR 2•61, 95% CI 2•59 to 2•64), and alcohol intoxication (OR 2•59, 95% CI 2•56 to 2•64) declined among 15-18-year-olds during COVID-19, with no similar gender differences.Interpretation Our results suggest that COVID-19 has significantly impaired adolescent mental health. However, the decrease observed in substance use during the pandemic might be an unintended benefit of isolation, and might serve as a protective factor against future substance use disorders and dependence. Population-level prevention efforts, especially for girls, are warranted.Funding Icelandic Research Fund.

Adolescent substance use—the consumption of alcohol, tobacco, and other harmful drugs—remains a persistent global problem and has presented ongoing challenges for public health authorities and society. In response to the high rates of adolescent substance use during the 1990s, Iceland has pioneered in the development of the Icelandic Model for Primary Prevention of Substance Use—a theory-based approach that has demonstrated effectiveness in reducing substance use in Iceland over the past 20 years. In an effort to document our approach and inform potentially replicable practice-based processes for implementation in other country settings, we outline in a two-part series of articles the background and theory, guiding principles of the approach, and the core steps used in the successful implementation of the model. In this article, we describe the background context, theoretical orientation, and development of the approach and briefly review published evaluation findings. In addition, we present the five guiding principles that underlie the Icelandic Prevention Model’s approach to adolescent substance use prevention and discuss the accumulated evidence that supports effectiveness of the model. In a subsequent Part 2 article, we will identify and describe key processes and the 10 core steps of effective practice-based implementation of the model.

Substance use among adolescents in Iceland has declined steadily from 1997 to 2014, while primary prevention factors for substance use have increased in strength during the same time-period.

Limiting the disruption of daily operations in schools while at the same time ensuring both quality and clarity of data collection procedures in school-based surveys are of paramount importance for researchers, school personnel, and students.

This is the second in a two-part series of articles about the Icelandic Model for Primary Prevention of Substance Use (IPM) in this volume of Health Promotion Practice. IPM is a community collaborative approach that has demonstrated remarkable effectiveness in reducing substance use initiation among youth in Iceland over the past 20 years. While the first article focused attention on the background context, theoretical orientation, evaluation and evidence of effectiveness, and the five guiding principles of the model, this second article describes the 10 core steps to practical implementation. Steps 1 to 3 focus on building and maintaining community capacity for model implementation. Steps 4 to 6 focus on implementing a rigorous system of data collection, processing, dissemination, and translation of findings. Steps 7 to 9 are designed to focus community attention and to maximize community engagement in creating and sustaining a social environment in which young people become progressively less likely to engage in substance use, including demonstrative examples from Iceland. And Step 10 focuses on the iterative, repetitive, and long-term nature of the IPM and describes a predictable arc of implementation-related opportunities and challenges. The article is concluded with a brief discussion about potential variation in community factors for implementation.