Attention-Deficit/Hyperactivity Disorder

Attention-deficit/hyperactivity disorder (ADHD) is a neurodevelopmental disorder defined by a persistent pattern of inattention and/or hyperactivity-impulsivity that is more frequent and severe than is typical for a person's developmental level and that interferes with functioning across more than one setting. Symptoms begin in childhood, and the condition often continues into adolescence and adult life.

Definition

ADHD is a neurodevelopmental disorder characterized by an age-inappropriate, persistent pattern of inattention and/or hyperactivity-impulsivity, with several symptoms present before age 12, occurring in two or more settings and causing functional impairment.

Scope

The entry covers ADHD as a clinical and neurodevelopmental entity: its core symptom dimensions, the requirement for early onset and cross-situational impairment, its high heritability and frequent co-occurrence with other disorders, and its developmental course. It is a reference description of the condition and not a source of diagnostic or treatment advice.

Core questions

• How are the inattentive and hyperactive-impulsive symptom dimensions defined and combined into presentations?
• What distinguishes ADHD from developmentally normal levels of activity and distractibility?
• Why is ADHD considered a neurodevelopmental rather than a purely behavioural disorder?
• How does the condition change across the lifespan?

Key concepts

• Inattention dimension
• Hyperactivity-impulsivity dimension
• Onset before age 12
• Cross-situational impairment
• Executive function and self-regulation
• High heritability
• Comorbidity (e.g., learning, oppositional, anxiety disorders)

Mechanisms

ADHD is highly heritable, with twin studies estimating heritability around 70 to 80 percent and risk arising from many common variants of small effect together with rarer variants. At the neural level it is associated with differences in fronto-striatal and other distributed networks that support attention, response inhibition, and reward processing, and with maturational delay in some cortical regions. No single biomarker defines the disorder; the diagnosis rests on the behavioural pattern. These neurobiological accounts describe group-level associations rather than tests applicable to an individual.

Clinical relevance

Understanding ADHD as an early-onset, cross-situational pattern of inattention and hyperactivity-impulsivity informs how clinicians, teachers, and families interpret a child's difficulties with sustained attention, organization, and self-regulation. This entry describes the disorder for reference; it does not provide individualized diagnostic criteria thresholds for clinical decisions or any treatment recommendations.

Epidemiology

ADHD is among the most common childhood neurodevelopmental disorders, with meta-analytic prevalence estimates of roughly 5 to 7 percent in children and adolescents worldwide. It is diagnosed more often in boys than girls, partly reflecting more prominent hyperactive-impulsive presentation in boys, and a substantial proportion of affected children continue to have impairing symptoms in adulthood.

Evidence & guidelines

DSM-5-TR and ICD-11 (where the corresponding category is 6A05) provide the diagnostic frameworks, requiring early onset, persistence, cross-situational symptoms, and functional impairment. Consensus reviews such as the Nature Reviews Disease Primers summary synthesize the genetic, neurobiological, and epidemiological evidence base. Diagnosis is clinical and based on developmental history and corroborating information across settings.

History

Descriptions of restless, inattentive children appear in the medical literature from the early twentieth century, and the condition was labelled in successive diagnostic systems as minimal brain dysfunction, hyperkinetic reaction, attention deficit disorder, and, from DSM-III-R and DSM-IV onward, attention-deficit/hyperactivity disorder. DSM-5 reclassified it explicitly as a neurodevelopmental disorder and recognized its persistence into adulthood.

Debates

Categorical diagnosis versus a dimensional trait

Because attention and activity vary continuously in the population, there is debate over whether ADHD marks a distinct category or the extreme of a continuous, partly heritable trait, with implications for diagnostic thresholds.

Key figures

• Stephen Faraone
• Russell Barkley
• Luis Augusto Rohde
• Anita Thapar

Seminal works

• faraone-2015
• polanczyk-2015

Frequently asked questions

Is ADHD a childhood-only condition?

No. Symptoms begin in childhood, but a substantial proportion of people continue to experience impairing inattention or hyperactivity-impulsivity into adolescence and adulthood.

Is ADHD inherited?

ADHD is strongly heritable; twin studies estimate heritability around 70 to 80 percent, with risk arising from many genetic variants of small effect alongside environmental contributions.