Attention-Deficit/Hyperactivity Disorder

Attention-deficit/hyperactivity disorder (ADHD) is a neurodevelopmental condition defined by a persistent pattern of inattention and/or hyperactivity-impulsivity that is greater than expected for a child's developmental level and that interferes with functioning across settings. It begins in childhood and, for many, continues into adolescence and adulthood.

Definition

Attention-deficit/hyperactivity disorder is a neurodevelopmental disorder defined by a persistent, developmentally excessive pattern of inattention and/or hyperactivity-impulsivity, with several symptoms present before age 12, occurring in more than one setting and causing functional impairment.

Scope

This entry covers the defining features, presentations, prevalence, and conceptual framing of ADHD in children and adolescents, together with its developmental course and frequent co-occurrence with other conditions. It is a reference overview of how ADHD is described and studied and does not provide diagnostic criteria for individual children or treatment guidance.

Core questions

• How is developmentally excessive inattention or hyperactivity distinguished from normal childhood behaviour?
• Why does ADHD present differently across ages and settings?
• To what extent does childhood ADHD persist into adulthood?

Key concepts

• Inattention
• Hyperactivity and impulsivity
• Symptom onset before age 12
• Cross-setting impairment
• Predominantly inattentive, hyperactive-impulsive, and combined presentations
• Persistence into adulthood

Key theories

Executive function and self-regulation models

Frame ADHD as involving difficulties in executive processes such as inhibitory control, working memory, and the regulation of attention and effort; influential as cognitive accounts but not a single unifying cause.

Mechanisms

ADHD is highly heritable and polygenic, with genetic risk interacting with prenatal and early-environmental factors. Neurobiological accounts implicate differences in fronto-striatal and other distributed networks involved in attention, inhibition, and reward, with dopaminergic and noradrenergic signalling featuring prominently. Cognitive models emphasise executive-function and self-regulation difficulties, while motivational accounts highlight altered sensitivity to delay and reward; no single mechanism explains all cases.

Clinical relevance

ADHD is one of the most common reasons children are referred for behavioural and developmental assessment, and it affects learning, relationships, and daily functioning. Understanding its features helps clinicians and educators interpret behaviour developmentally. This entry describes how the condition is conceptualised and studied and is not a basis for diagnosing or managing an individual child, which requires specialist assessment.

Epidemiology

Meta-analyses estimate a worldwide childhood prevalence of ADHD of roughly 5-7 percent, with variation across studies driven largely by differences in diagnostic criteria and ascertainment rather than true geographic differences. ADHD is identified more often in boys than girls in childhood, frequently co-occurs with other neurodevelopmental, learning, and emotional disorders, and symptoms persist into adolescence or adulthood in a substantial proportion of cases.

Evidence & guidelines

Diagnostic concepts follow DSM-5-TR, which recognises inattentive, hyperactive-impulsive, and combined presentations, and ICD-11. Diagnosis is clinical, based on developmental history and corroborating information across settings rather than a biological test. Comprehensive reviews summarise the evidence base, and clinical pathways are issued by bodies such as the American Academy of Pediatrics and the UK National Institute for Health and Care Excellence; this entry summarises framing rather than reproducing those pathways.

History

Descriptions of restless, inattentive children appear in the early twentieth-century medical literature, and the condition was labelled in successive classifications as hyperkinetic reaction, attention deficit disorder, and then attention-deficit/hyperactivity disorder. DSM-III (1980) emphasised inattention, later editions recognised symptom subtypes or presentations, and DSM-5 (2013) reclassified ADHD as a neurodevelopmental disorder and raised the onset criterion to before age 12.

Debates

Thresholds and concerns about over- and under-diagnosis

Because attention and activity are continuously distributed, where to set the diagnostic threshold is contested, with debate over both over-diagnosis in some settings and under-recognition in others, including in girls and in adults.

Key figures

• Stephen Faraone
• Anita Thapar
• Russell Barkley

Seminal works

• faraone-2015
• thapar-2016

Frequently asked questions

Is ADHD only a childhood condition?

No. ADHD begins in childhood, but for a substantial proportion of people symptoms and impairment persist into adolescence and adulthood, though the presentation often changes with age.

Can ADHD be diagnosed with a brain scan or blood test?

No. Diagnosis is clinical, based on a developmental history and information about symptoms and impairment across more than one setting, not on any biological test.