Paediatric versus adult ADHD.

ADHD has long been framed as a childhood condition, with the assumption that symptoms diminish during adolescence and early adulthood. This view is increasingly difficult to sustain. A growing body of research shows that ADHD frequently persists into adulthood, challenging the notion of it being a transient developmental disorder and positioning it instead as a lifespan condition.

What has changed is not only recognition, but scale. Adult ADHD, once considered relatively rare, is now understood to be common. Longitudinal studies suggest that in approximately 40–60% of cases, individuals continue to meet full diagnostic criteria in adulthood, while up to 90% retain at least some symptoms. Globally, around 2.5% of adults are estimated to have persistent ADHD (with childhood onset), and nearly 7% meet criteria for symptomatic adult ADHD regardless of onset—equating to hundreds of millions of adults worldwide. At the same time, prevalence appears to decline with age, with higher rates observed in young adults and substantially lower rates in older populations.

Diagnosis in adulthood remains complex and, at times, contested. On one hand, ADHD in adults is widely underdiagnosed or misdiagnosed, often overlooked when symptoms present differently than in childhood. On the other, increased awareness has raised concerns about potential overdiagnosis and overtreatment. This tension reflects ongoing ambiguity in diagnostic frameworks and contributes to inconsistent prevalence estimates.

Importantly, ADHD does not simply persist unchanged—it evolves. While hyperactivity tends to emerge early and often decreases with age, inattentive symptoms are typically more stable. In adults, ADHD is less likely to present as overt hyperactivity and more often manifests as distractibility, mind-wandering, difficulty sustaining effort, and challenges with goal-directed behaviour. Symptoms may appear less visible externally, partly due to the development of compensatory strategies, which can mask underlying difficulties.

Taken together, current evidence supports a shift in perspective: ADHD is not confined to childhood but represents a condition that can persist across the lifespan, with changing expression rather than simple remission.