Increase in Occurrence of Attention Deficit Hyperactivity Disorder Differs by Age Group and Gender-Finnish Nationwide Register Study.

introductionThis study describes epidemiology of attention deficit hyperactivity disorder (ADHD) and use of ADHD medication across all age groups in Finland.

methodsThis retrospective study is based on nationwide registers in Finland. The study population included individuals with ADHD diagnosis and/or an ADHD medication record at least once during 2015-2020.

resultsThe yearly prevalence of ADHD was higher in males than in females and was highest in the age groups of 6- to 12- and 13- to 17-year-old males. In 2020, the yearly prevalence was 4.2% in ≤12-year-old, 6.7% in 13- to 17-year-old, 0.7% in ≥18-year-old males, and 1.1%, 2.6%, and 0.6%, respectively, in females. The gender-related differences were greatest among 6- to 12- and 13- to 17-year-olds, after which the differences evened out. During the study period from 2015 to 2020, the yearly prevalence more than doubled in each of the five Finnish administrative university hospital areas. The prevalence was higher in males, but the relative growth was higher in females compared to males. The incidence per 100,000 inhabitants was the highest in ≤12-year-old males and increased in all age groups and in both genders. The use of medication was more common in males than in females, and the overall proportion of prevalent ADHD patients on medication remained around 80%. Decrease in medication use was observed in connection with the transition from adolescence to adulthood, in both genders.

conclusionBoth prevalence and incidence of ADHD more than doubled in Finland during the study period 2015-2020. This study presents the most comprehensive analysis of national register data at personal-level linkage in Finland, since it included all age groups, and both diagnosed ADHD patients and individuals receiving medication, not limited to reimbursed medication.