Background: Attention deficit hyperactivity disorder (ADHD) is present in about a quarter of patients with a substance use disorder (SUD) and impulsivity is a key feature of both disorders. However, very little is known about differences in impulse control and other cognitive functions between ADHD patients with and without SUD.
Methods: In adult male medication-naïve ADHD patients with and without comorbid cocaine dependence and healthy controls (matched on gender, age and IQ), we measured motor impulsivity (stop signal task), cognitive impulsivity (delay discounting task), divided attention (trail making test), interference (Stroop task), working memory (n-back task), and time reproduction (time reproduction task). Additionally, self-reported ADHD symptoms (using the ADHD Symptom Rating Scale; ASRS) and self-reported impulsivity (Barratt Impulsivity Scale; BIS) were assessed.
Results: Significantly higher levels of motor and cognitive impulsivity were found in ADHD patients with comorbid cocaine dependence compared to ADHD patients without cocaine dependence and controls, and both measures of impulsivity were highly correlated. No significant group differences were found on other cognitive measures. With regard to the self-report measures, only BIS attention subscores differed significantly between ADHD patients with and without cocaine dependence. ASRS and BIS scores were not significantly correlated.
Conclusion: This is the first study showing that ADHD patients with cocaine dependence are a distinctly more impulsive subpopulation compared to ADHD patients without cocaine dependence on objective measures of impulsivity. These findings are relevant to optimize psycho-education and treatment of ADHD patients with comorbid SUD.
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