• Adult ADHD
• Attention deficit hyperactivity disorder
• Dual disorder
• Substance use disorder

Background: Attention deficit hyperactivity disorder (ADHD) albeit considered a childhood-onset neurodevelopmental condition, is nevertheless a frequent and disabling condition in adults. Substance Use Disorders (SUD) are particularly common among adults with ADHD and are associated with an early onset of SUD, a more severe course, an high risk of polysubstance abuse, reduced treatment adherence and worse response to stimulant therapies. Our study proposes to explore substance use patterns among adult ADHD (A-ADHD) patients and to compare clinical, temperamental and functional features in A-ADHD with (A-ADHD/SUD) and without (A-ADHD) a substance use disorder.
Methods: Participants included 102 adults who fulfilled DSM-5 criteria for ADHD admitted between 2016 and 2019 to the Outpatient Clinic of the Second Psychiatric Unit of the University of Pisa. All patients were assessed using the Diagnostic Interview for ADHD in adults (DIVA 2.0), the Conners’ Adult ADHD Rating Scales–Observer: Short Version (CAARS-O:S), the Structured Clinical Interview for Axis I and II Disorders (SCID-I/II), the brief Temperament Evaluation of Memphis, Pisa, Paris and San Diego-M (TEMPS-M), the Barratt Impulsiveness Scale (BIS-11), the Brief Psychiatric rating scale (BPRS), the Reactivity Intensity Polarity Stability Questionnaire (RIPoSt-40), the Difficulties in Emotion Regulation Scale (DERS), the WHODAS 2.0 and the Functioning Assessment Short Test (FAST). We performed a factorial analysis in order to clusterize our patients in different typology of substance use; then, we divided the sample into ADHD patients with (A-ADHD/SUD) and without SUD (A-ADHD). Comparisons between the two groups were conducted using chi-square test for categorical variables and Student's t-test for continuous variables. Logistic regression analysis was used to identify the predictive value of the diagnostic, temperamental and functional variables associated with A-ADHD/SUD.
Results: In our sample 50 (49%) patients had a comorbid SUD (A-ADHD/SUD). The substances most used were cannabis (90%), cocaine (72%), alcohol (58%) MDMA (36%), amphetamines (28%), opioids (20%) and benzodiazepines (20%). The factorial analysis revealed three patterns of SUD: the first (Type 1) characterized by co-use of stimulants, cocaine and alcohol (N=14); the second (Type 2) characterized by co-use of cocaine, stimulants, SNC depressors and THC (N=11) and the third characterized by THC mono-use (N=25)(Type 3). Patients who used only THC (Type 3) were significantly younger than poly-users (Type 2). Type 2 group showed higher scores at the BPRS ‘Anxiety-Depression’ domain (p= 0.013) and at the total BPRS severity score (p= 0.024) compared to both the other patterns. Only the FAST ‘interpersonal’ subscale scored higher in the Type 2 group (p=0.020) compared to THC mono-users (Type 3). A-ADHD/SUD patients were more unemployed (p= 0.009), had more legal problems (p=0.001) and showed higher rates of borderline personality disorder (p=0.05) and antisocial personality disorder (p=0.037). Conversely, A-ADHD/SUD group had significantly less social phobia (p=0.017) and autism spectrum disorders (p=0.053) than A-ADHD.
A-ADHD/SUD patients showed less inattentive symptoms (DIVA 2.0) (p=0.047) and higher Hyperactive/Impulsive symptoms (CAARS-O:S) (p=0.013) but the ADHD severity index was similar to that of A-ADHD patients (p=0.696). Discriminant analysis showed that the variables that differentiated A-ADHD/SUD patients were Irritable temperament (p=0.024), BPRS Hostile-Suspiciousness (p=0.002), BIS Motor impulsiveness (p=0.003), RIPoSt Emotional Impulsivity (p=0.05), DERS Awareness (p=0.023) and FAST Financial (p=0.003) subscales.
At the logistic regression analysis the most discriminant factors of ADHD/SUD patients were the presence of ‘legal problems’, the ‘financial’ impairment and the ‘Hostile-Suspiciousness’ BPRS subscale; the presence of social phobia was the only variable that differentiated the A-ADHD group from the A-ADHD/SUD one.
Conclusions: Our results showed high rates of SUD comorbidity (50%) in adult ADHD patients with a predominant use of THC, stimulants and poly substance use. Given SUD severity, poly users displayed more interpersonal difficulties and more psychopathology. ADHD/SUD patients showed more hyperactivity/impulsivity symptoms suggesting a major role of impulsiveness traits in the use of substances. As substances of abuse are known to increase the release of dopamine in the brain reward center, besides the ‘rewarding’ effect, we hypothesized that at the beginning substances use could be an attempt to ameliorate the specific ADHD symptomatology. However, the trajectories of SUD are not stable and progressively patients tend to develop poly abuse conducts, drug dependence, psychiatric symptoms with higher dysfunction in several contexts. Stimulants and non-stimulants medications should be used to improve ADHD symptomatology in Dual Disorder patients but their efficacy on SUD is still debating. We believe that an early recognition of ADHD associated with a prompt psychopharmacological treatment will reduce the incidence and the consequences of SUD.