Substance Use in Adolescents with ADHD and Bipolar Spectrum Disorders: The Transdiagnostic Role of Emotional Dysregulation, Impulsivity and Hypersensitivity Traits

Background/Objectives: Adolescents with attention-deficit/hyperactivity disorder (ADHD) and bipolar spectrum disorders are at increased risk of substance use; categorical diagnoses may not fully explain individual variability in substance-related outcomes. This study examined substance use severity in clinically complex adolescents, focusing on the role of primary diagnosis and transdiagnostic dimensions (emotional dysregulation, impulsivity, cyclothymic-hypersensitive traits). Methods: In this cross-sectional observational study, 47 adolescents (aged 14–17) with DSM-5 diagnoses of ADHD or bipolar spectrum disorders were recruited from two Italian child and adolescent mental health services. Substance use severity was assessed using the Q-PAD Substance Abuse scale and the ABQ. Emotional dysregulation, impulsivity, affective temperament, and emotional-behavioral problems were assessed through RIPOST-Y, BIS-11, CHT-Q, and YSR. Correlation studies and group comparisons based on the Q-PAD Substance Abuse scale were performed to explore associations between clinical features and substance use. Results: Substance use severity was elevated in the overall sample and was not significantly associated with primary diagnostic category, overall illness severity, or global functioning. Higher Q-PAD Substance Abuse scores were significantly associated with impulsivity, emotional dysregulation, and hypersensitivity traits. Later initiation of lithium treatment was also associated with greater substance use severity. Conclusions: In this sample, substance use severity was more related to dimensional transdiagnostic vulnerabilities than to categorical diagnosis. Although preliminary and exploratory, these findings support early identification and targeted intervention on emotional dysregulation and impulsivity as potentially modifiable risk factors for adolescent substance use.