Late-Onset ADHD: Understanding the Evidence and Building Theoretical Frameworks

Purpose of Review The traditional definition of Attention-Deficit/Hyperactivity Disorder (ADHD), assuming onset in childhood, has been challenged by evidence from four recent birth-cohort studies that reported most adults with ADHD lacked a childhood categorical ADHD diagnosis. Recent Findings Late onset of symptoms was evaluated in the long-term follow-up of the Multimodal Treatment study of ADHD (MTA). In most cases, other factors were present that discounted the late onset of ADHD symptoms and excluded the diagnosis of ADHD. Summary We offer two theoretical frameworks for understanding the ADHD trajectory throughout the life cycle: (1) the complex phenotype model, and (2) the restricted phenotype model. We conclude that (a) late onset (after age 12) is a valid trajectory for ADHD symptoms, (b) the percentage of these cases with onset after adolescence is yet uncertain, and (c) the percentage meeting exclusion criteria for diagnosis of ADHD is influenced by the rigor of the methodology used to obtain evidence and whether or not DSM exclusionary criteria are applied.