Neurobiological and cognitive theories implicate deficits in executive function (EF) as a core facet of both depressive disorders and attention-deficit/hyperactivity disorder (ADHD), but empirical investigations inconsistently support this conclusion. Despite recognition of the likely bi-directional relationship of EF deficits to depression and ADHD, respectively, the extent to which comorbid depression might impact EF in adults remains unclear, considering more of the literature has examined children and adolescents. This study examined performance differences on EF measures in clinically-referred adults diagnosed with ADHD or a non-ADHD primary psychopathological condition in the presence/absence of comorbid depression.

This cross-sectional study included data from 404 adults referred for neuropsychological evaluation at a Midwestern academic medical center. In total, 343 met DSM-5 diagnostic criteria for ADHD (ADHD-all group:164 Predominantly Inattentive presentation [ADHD-I] and 179 Combined presentation [ADHD-C]) and 61 met criteria for a non-ADHD primary psychopathological condition (psychopathology group: 31 mood disorder, 17 anxiety disorder, and 13 posttraumatic stress disorder) when assessed via semi-structured clinical interview. All patients completed the Beck Depression Inventory-Second Edition (BDI-II) and five EF tests: Letter Fluency, Trail Making Test-Part B (Trails-B), Stroop Color and Word Test Color-Word trial (SCWT CW); and WAIS-IV Working Memory Index (WMI). Oneway MANOVAs assessed for significant EF differences between groups with high (BDI-II greater than or equal to 20) or low (BDI-II less than or equal to 19) depressive symptoms.

When group diagnosis (ADHD-all vs. psychopathology) was examined in the context of high or low depression, a significant difference in EF performance emerged between groups, F(12, 1042.72)=2.44, p<.01, Wilk's A=.93, partial n2=.02, with univariate analyses indicating a significant difference in FAS-T between at least two of the groups (F(3, 397)=3.92 , p< .01, partial n2=.03). Tukey's HSD Test for multiple comparisons found that the mean value of FAS-T was significantly different between the ADHD-high depression and ADHD-low depression groups (p=.046 , 95% CI = [5.81, -.04]) as well as between the ADHD-low depression and psychopathology-high depression groups (p=.05, 95% CI = [-8.89, .00]). A one-way MANOVA examining differences between groups when distinguishing ADHD by subtype revealed a statistically significant difference in EF performance between groups, F(20, 1301)=1.85, p<.05, Wilk's A=.91, partial n2=.02, with univariate analyses indicating a statistically significant difference in FAS-T between at least two of the groups (F(5, 395) = 2.39 , p<.05, partial n2 = .03). However, Tukey's HSD Test for multiple comparisons found that the mean value of FAS-T was not significantly different between any of the groups.

Overall, results indicate that clinically-referred patients with ADHD perform comparably on tests of EF regardless of the presence or absence of comorbid depression. These findings have implications for conceptualizing EF weaknesses in neuropsychological profiles for individuals with ADHD and suggest examining factors beyond comorbid depression.