The deCODE cohort consisted of 8,281 individuals with ADHD. These were either individuals with a clinical diagnosis of ADHD (n = 5,583) according to the ICD10 criteria (ICD10-F90, F90.1, F98.8) or individuals that have been prescribed medication specific for ADHD symptoms (ATC-NA06BA, mostly methylphenidate) (n = 2,698). The control sample did not contain individuals with a diagnosis of SCZ, BD, ASD or self-reported ADHD symptoms or diagnosis. All participants who donated samples gave informed consent. Information about genotyping, QC and evaluation of potential genetic heterogeneity between individuals identified based on diagnosis codes and medication can be found in the Supplementary Note.
