https://doi.org/10.1177/0004867417700274 Australian & New Zealand Journal of Psychiatry 1–23 DOI: 10.1177/0004867417700274 © The Royal Australian and New Zealand College of Psychiatrists 2017 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav journals.sagepub.com/home/anp Australian & New Zealand Journal of Psychiatry Introduction Depressive disorders, including major depressive disorder (MDD) and dysthymic disorder (DD), are a leading cause of global burden of disease (Ferrari et al., 2013). While MDD is a relatively rare diagnosis in childhood, the inci- dence of the disorder rises rapidly during adolescence and early adulthood (Hankin et al., 1998; Lewinsohn et al., 1993, 1998). In all, 40% of MDD patients have suffered their first depressive episode by the age of 20 (Eaton et al., 2008), and 50% of patients experiencing MDD before the age of 18 will have further mood episodes in adulthood (Kessler et al., 2001). These numbers have provided an argument for early intervention strategies in MDD that can target symptoms early and prevent progression to a chronic illness stage (Allen et al., 2007). However, intermittent subthreshold depressive symptoms affect 10–20% of all young people (for review, see Wesselhoeft et al., 2013) and may represent a maturational process occurring in a devel- opmental window similar to memory and fear development (King et al., 2013). Targeting evidence-based interventions to those most in need therefore remains a major challenge for clinicians and policy-makers (Jorm, 2015; Purcell et al., 2015). Depressive symptom trajectories in late adolescence and early adulthood: A systematic review Klaus Oliver Schubert 1,2 , Scott R Clark 1 , Linh K Van 1 , Jane L Collinson 1 and Bernhard T Baune 1 Abstract Objective: In adolescents and young adults, depressive symptoms are highly prevalent and dynamic. For clinicians, it is difficult to determine whether a young person reporting depressive symptoms is at risk of developing ongoing mood difficulties or whether symptoms form part of a transient maturational process. Trajectory analyses of longitudinally assessed symptoms in large cohorts have the potential to untangle clinical heterogeneity by determining subgroups or classes of symptom course and their risk factors, by interrogating the impact of known or suspected risk factors on tra- jectory slope and intercept and by tracing the interrelation between depressive symptoms and other clinical outcomes over time. Method: We conducted a systematic review of trajectory studies conducted in cohorts including people aged between 15 and 25 years. Results: We retrieved 47 relevant articles. These studies suggest that young people fall into common mood trajec- tory classes and that class membership and symptom course are mediated by biological and environmental risk factors. Furthermore, studies provide evidence that high and persistent depressive symptoms are associated with a range of concurrent health and behavioral outcomes. Conclusion: Findings could assist in the formulation of novel concepts of depressive disorders in young people and inform preventive strategies and predictive models for clinical practice. Keywords Depressive symptoms, trajectory, young people, adolescents, youth mental health 1 Discipline of Psychiatry, The University of Adelaide, Adelaide, SA, Australia 2 Lyell McEwin Hospital, Northern Adelaide Local Health Network, Mental Health Service, Adelaide, SA, Australia Corresponding author: Klaus Oliver Schubert, Discipline of Psychiatry, The University of Adelaide, Adelaide, 5005, SA, Australia. Email: oliver.schubert@adelaide.edu.au 700274ANP 0 0 10.1177/0004867417700274ANZJP ArticlesSchubert et al. review-article 2017 Review