Attention-deficit/hyperactivity disorder (ADHD) and depression commonly co-occur. Identifying children with ADHD at risk for later depression may allow early intervention and prevention. Irritability is one possible mechanism linking these two disorders. It is common in ADHD and associated with later depression in the general population. Cross-sectional studies suggest an association between irritability and depression in ADHD, but longitudinal research is limited. This study followed up a clinical ADHD sample longitudinally to examine: (1) the association between childhood irritability and later depression symptoms, and (2) whether irritability persistence is important in this association. At baseline, parents (n = 696) completed semi-structured interviews about their child (mean age = 10.9), providing information on child psychopathology, including irritability. A subsample (n = 249) was followed up after a mean of 5.4 years. Parent-completed Mood and Feelings Questionnaires provided information on depressive symptoms at follow-up. Parent-rated structured diagnostic interviews provided information on ADHD diagnosis and irritability at follow-up. Regression analyses examined associations between (i) baseline irritability and depression symptoms at follow-up, and (ii) persistent (vs. remitted) irritability and depression symptoms at follow-up. Analyses controlled for age, gender, depression symptoms, anxiety, ADHD symptoms, and ADHD medication at baseline. Baseline irritability was associated with depression symptoms at follow-up, but the association attenuated after controlling for anxiety and ADHD symptoms. Persistent irritability was associated with depression symptoms at follow-up, after including all covariates. Children with ADHD with persistent irritability are at elevated risk of developing depression symptoms. They may be a target for early intervention and prevention of depression.
Keywords: ADHD; DMDD; Depression; Irritability.