To Örebro University

Background: A better understanding of the trajectories and economic burden of psychiatric and somatic disorders (multimorbidity) in ADHD from childhood to adulthood is important for guiding more targeted areas for treatment of ADHD and prevention of multimorbidity, and for forecasting demands on the medical infrastructure. This study aimed to investigate patterns of healthcare utilization and costs of multimorbidity across young adulthood in individuals with a childhood ADHD diagnosis, and additionally in individuals who continue to have ADHD-related contact with health services (persisters) and those who do not (remitters).

Methods: We prospectively followed a cohort (N = 445,790) born 1987-1990 from the ages of 18 to 26 years. Data on healthcare utilization were obtained from the Swedish National Patient Register (inpatient and outpatient care) and the Prescribed Drug Register (medication prescriptions).

Results: Mean annual costs per capita from multimorbidity was euro890 ($1,223) in individuals with a childhood ADHD diagnosis (persisters/remitters: euro1,060[$1,456]/euro609[$837]) and euro304 ($418) in individuals without. Costs were largely driven by inpatient hospital admissions, mainly from drug abuse and injuries. Healthcare utilization and costs of psychiatric and somatic disorders at 18 years was significantly higher in individuals with childhood ADHD compared to those without. These group differences remained stable or increased across young adulthood for most outcomes and were generally larger in women than in men. ADHD remitters continued to show significantly greater healthcare utilization and costs compared to individuals without childhood ADHD, although their profiles were not as severe as ADHD persisters.

Conclusions: Childhood ADHD has long-term associations with both psychiatric and somatic disorders. Findings demonstrate the individual and societal burden of ADHD in adulthood and highlight the importance of continued support from childhood-adolescent to adult health services and early prevention of multimorbidity. Findings also point to specific targets for intervention that may be effective, such as drug abuse and injuries.