Predictors of treatment success in patients with substance use disorder (SUD) and co-morbid attention deficit/hyperactivity disorder (ADHD): Results from the International Naturalistic Cohort Study of ADHD and SUD (INCAS).

Comorbid attention deficit/hyperactivity disorder (ADHD) and substance use disorder (SUD) is associated with poor treatment outcomes. This international multi-center observational prospective cohort study aimed to gain knowledge about predictors of treatment outcomes in adult SUD+ADHD patients. Data was collected from June 2017 to May 2021 at baseline, four weeks, three months, and nine months at twelve treatment services in nine countries. Main outcomes were: Treatment retention, ≥30% reduction from baseline to follow-up according to the adult ADHD self-report scale (ASRS-18), and self-reported substance use at three-month follow-up. A total of 137 adult females (24 %) and 441 adult males (76 %) were enrolled. Receiving stimulant treatment for ADHD was significantly associated with better treatment retention (OR: 2·4, 95% CI: 1·4-4·2), ≥30% reduction in ASRS total score (OR: 2·6, 95% CI: 1·2-6·1), and fewer heavy drinking days (IRR: 0·24, 95% CI: 0·13-0·42) at three months. Psychosocial treatment for ADHD was independently and significantly associated with fewer heavy drinking days at three months (IRR: 0·27, 95% CI: 0·14-0·51). In summary, treatment of ADHD in SUD+ADHD patients was related to improvements in ADHD-symptoms, treatment retention and fewer heavy drinking days at follow-up. These findings highlight the importance of ADHD treatment provision in this population. Future RCTs are warranted to confirm these results and should assess combinations of ADHD treatments and SUD treatments using different doses of stimulants. Trial Registration: ISRCTN (https://doi.org/10.1186/ISRCTN15998989).