Developmental course of anxiety and depression from adolescence to young adulthood in a prospective Norwegian clinical cohort.

Anxiety and depression are often co-occurring disorders, reflecting both homotypic and heterotypic continuity as possible developmental pathways. The present study aimed to examine homotypic and heterotypic continuities of anxiety and depression across 3 years in adolescence and young adulthood. Participants included patients presenting to psychiatric care with diagnoses of anxiety and/or depressive disorders aged 13-18 at T1 (N = 717, 44% initial participation rate) and aged 16-21 at T2 (N = 549, 80% follow-up participation rate). McNemar's mid-p test and ordinal proportional odds logistic regression analyses were used to assess changes in prevalence within and across diagnostic categories, respectively. More adolescents had an anxiety disorder (+ 11%), whereas fewer had a depressive disorder (- 11%), at T2 compared to T1. Of adolescents with anxiety and/or depression at T1, only 25% recovered or were non-symptomatic 3 years after referral to a psychiatric clinic. Homotypic continuity was observed for anxiety disorders in general (OR = 2.33), for phobic anxiety disorders (OR = 7.45), and for depressive disorders (OR = 2.15). For heterotypic continuity, depression predicted later anxiety (OR = 1.92), more specifically social anxiety (OR = 2.14) and phobic anxiety disorders (OR = 1.83). In addition, social anxiety predicted later generalized anxiety disorder (OR = 3.11). Heterotypic continuity was thus more common than homotypic continuity. For adolescents presenting with anxiety or depression, treatment should, therefore, target broad internalizing symptom clusters, rather than individual diagnoses. This may contribute to prevent future mental illness, particularly anxiety, in clinical samples.