The impact of initial depression and anxiety levels on symptom severity change during psychological treatment for common mental disorders: a systematic review

Depression and anxiety are highly comorbid conditions, which may impact treatment response. We intended to examine how depression and anxiety symptoms change during psychological interventions for adults and how the initial severity is associated with distinct trajectory classes. We identified papers examining longitudinal changes in depression and anxiety. Trajectory classes were grouped into responders, improvers and non-improvers. Narrative synthesis, alongside meta-analysis, was applied to explore the number and nature of classes, their associations with study characteristics and predictors of trajectory class membership. This study was pre-registered on International Prospective Register of Systematic Reviews (PROSPERO) (CRD42023393155), and the authors followed Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidance. We identified 18 papers, including 22 models with two to six classes. Responding and non-improving classes prevailed. Meta-regression revealed no characteristics associated with the proportion of these classes. Initial depression and anxiety levels predicted trajectory class membership for each other, but not always non-response. Unemployment, suicidality, social functioning impairment, treatment type and medication use predicted following non-responding trajectory. Our findings highlight the complex relationship between initial anxiety and depression severity and their changes during psychological interventions. They provide practitioners with insights into factors associated with non-response patterns of symptom change.