Is there evidence for additive neurocognitive deficits in adults with attention-deficit/hyperactivity disorder and co-occurring conditions?

OBJECTIVE: Adults with attention-deficit/hyperactivity disorder (ADHD) frequently present with co-occurring anxiety and depressive symptoms, raising questions about whether such comorbidity is associated with additive neurocognitive impairment. Prior findings have been mixed and rarely account for symptom exaggeration or noncredible task engagement. This study examined whether adults with ADHD and elevated internalizing symptoms demonstrate additive neurocognitive deficits when symptom and performance validity are controlled. METHOD: Archival data were analyzed from 752 postsecondary students referred for psychoeducational/neuropsychological evaluation. Participants were classified into ADHD only, ADHD with elevated anxiety and/or depressive symptoms, anxiety only, depression only, and assessment-seeking clinical controls without formal diagnoses. Analyses were restricted to individuals who passed established presentation validity criteria. Neurocognitive performance was examined across intellectual functioning, executive functioning, memory, and academic achievement using mean-level comparisons and rates of scores at or below the 16th percentile. RESULTS: Across domains, group means generally fell within the average range with substantial overlap among groups. Adults with ADHD and co-occurring anxiety and/or depressive symptoms did not demonstrate poorer neurocognitive performance than adults with ADHD alone. Statistically significant group differences emerged on select measures but were small, inconsistent, and not specific to comorbid ADHD groups. Rates of low scores (e.g., ≤ 16th percentile) were comparable across groups. CONCLUSIONS: When presentation validity is established, co-occurring anxiety and/or depressive symptoms were not associated with consistent or clinically meaningful additive neurocognitive deficits in adults with ADHD. These findings underscore the importance of validity-controlled assessment and caution against inferring objective cognitive impairment solely from diagnostic comorbidity.