Inclusion Criteria  Age greater than or equal to (>=) 18 years at the beginning of the patient observation period (that is 18-months prior to the adult ADHD diagnosis to ensure they would have been seen in adult health care services). First record of an adult ADHD diagnosis between 01st January 2016 and 30th June 2018. Data availability in the database at least during the 18-months before and after the index date.  Exclusion Criteria  A participant will be excluded from the study if their CPRD linked to HES electronic medical record data includes:  Incomplete information for key demographics (that is, missing age or sex). Clinical history of a diagnosis of ADHD during childhood or adolescence. Prescription of a licensed adult ADHD medication (that is, methylphenidate, lisdexamfetamine, dexamfetamine, atomoxetine) during the pre-index period.