Interactive effect of irritability and negative life events on internalizing symptoms.

BACKGROUND AND OBJECTIVES: Childhood irritability and negative life events have been linked to internalizing symptoms; however, it remains unclear how these factors jointly shape symptom trajectories. DESIGN: We examined independent and interactive effects of irritability and negative life events on the development of depressive, anxiety, and somatic symptoms. METHODS: Participants included 9- to 10-year-old children (N = 11,868) from the Adolescent Brain Cognitive Development Study (ABCD Study®). Linear mixed-effects modeling was utilized to investigate the longitudinal trajectories of depressive, anxiety, and somatic symptoms across three annual follow-up assessments, with irritability, including both tonic and phasic irritability, negative life events, and their interaction included as predictors. RESULTS: Higher irritability and greater exposure to negative life events independently predicted changes in depressive, anxiety, and somatic symptom trajectories over time. Irritability and negative life events also interacted to predict depressive symptom trajectories, with greater negative life event exposure amplifying differences in depressive symptom trajectories across irritability levels. Similar patterns were observed for tonic and phasic irritability. No significant interactions were observed for anxiety or somatic symptom trajectories. CONCLUSIONS: Irritability and negative life events independently contribute to multiple domains of internalizing psychopathology, but their joint effects appear to be specific to depressive symptom development.