Study Preregistration: Clinical and Cognitive Mediators Underlying Subsequent Depression in Individuals With Attention-Deficit/Hyperactivity Disorder: A Developmental Approach.

Individuals with attention-deficit/hyperactivity disorder (ADHD) are about 5.5 times more likely to develop depression,¹ and this comorbidity is associated with greater impairment than either disorder alone. Although there is evidence that ADHD may play a causal role in the development of depression,^2,3 the underlying mechanisms remain poorly understood. Several clinical and cognitive mechanisms have been proposed: (1) clinical antecedents of depression, such as irritability and anxiety, often observed in individuals with ^4,5; (2) cognitive-affective functions (response inhibition, working memory, sustained attention, and emotion recognition) impaired in individuals with ADHD and, to a lesser extent, in depressed individuals^6,7; or (3) negative thought patterns underlying vulnerability to depression also observed in individuals with ADHD (external locus of control and negative cognitive styles).⁸ Nevertheless, few longitudinal studies have tested these as potential mediators between ADHD and subsequent depression. Existing studies are primarily cross-sectional, limited by small sample sizes, and have not examined developmental stage-specific effects. Therefore, we will explore the mediating role of clinical, cognitive-affective, and negative thought patterns, and whether their role varies by developmental stage and sex. We will examine all mediators simultaneously, the relative contribution of 3 categories of mediators, and the associations between ADHD and each hypothesized mediator/factor. We hypothesize the following: (1) ADHD will be more strongly associated with irritability and emotion recognition in childhood than in adolescence and young adulthood; (2) the association between ADHD and anxiety will be consistent across development; and (3) ADHD will be more strongly associated with response inhibition, working memory, sustained attention, external locus of control, and negative cognitive style in adolescence and young adulthood compared to childhood.