What is Adult ADHD? Attention-Deficit/Hyperactivity Disorder (ADHD) is a neurodevelopmental disorder that affects the brain’s ability to regulate attention and behaviour. Although it is typically diagnosed in childhood, it can still be present in adulthood. Under the Diagnostic and Statistical Manual of Mental Disorders (DSM-5), adult ADHD is identified by the patterns of inattention, hyperactivity, and impulsivity that can affect day-to-day activities. These symptoms can go unnoticed until...