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 developmentally inappropriate and interferes with functioning. It typically begins in childhood, frequently persists into adulthood, and is increasingly recognized across the lifespan in primary care.

Definition

ADHD is characterized by a persistent pattern of inattention (such as difficulty sustaining attention, distractibility, and disorganization) and/or hyperactivity-impulsivity (such as restlessness, excessive activity, and acting without forethought) that is inconsistent with developmental level, has an onset in childhood, occurs in more than one setting, and causes clinically significant impairment.

Scope

The entry covers the clinical concept of ADHD as a neurodevelopmental disorder, its core symptom domains and presentations, hypothesized mechanisms, and population burden. It treats ADHD as a reference topic within the family-medicine mental-health area and does not provide diagnostic instruments, dosing, or individualized treatment plans.

Core questions

• What are the core symptom domains and presentations of ADHD?
• How is ADHD distinguished from developmentally normal behaviour and from other conditions?
• What is known about the genetic and neurobiological basis of the disorder, and its course across the lifespan?

Key concepts

• Inattention domain
• Hyperactivity-impulsivity domain
• Predominantly inattentive, hyperactive-impulsive, and combined presentations
• Childhood onset and persistence into adulthood
• Executive function and self-regulation
• Heritability and polygenic risk
• Psychiatric comorbidity

Mechanisms

ADHD is described as a highly heritable, polygenic neurodevelopmental condition involving altered development and function of brain networks supporting attention, executive control, and reward processing, with dopaminergic and noradrenergic signaling featuring in neurobiological accounts. Reviews characterize it as the outcome of many small-effect genetic variants interacting with environmental factors, producing deficits in self-regulation rather than a single localized lesion; no biomarker establishes the diagnosis, which remains clinical.

Clinical relevance

ADHD is among the more common neurodevelopmental conditions seen in primary care, frequently co-occurs with learning, mood, anxiety, and substance-use problems, and is increasingly identified in adults as well as children. This entry describes the clinical concept and the evidence base for understanding it; it is educational reference material and is not a tool for diagnosing or treating an individual patient.

Epidemiology

ADHD affects a substantial minority of children worldwide, with most prevalence estimates in the low single-digit-to-around-five-percent range depending on criteria and setting, and it is more frequently diagnosed in boys than girls. A considerable proportion of childhood cases show persistence of symptoms or impairment into adulthood, and the disorder is associated with broad functional consequences across education, work, and relationships.

Evidence & guidelines

ADHD is defined in the DSM-5, which classifies it among neurodevelopmental disorders and recognizes adult diagnosis, and in the ICD-11 (attention deficit hyperactivity disorder, code 6A05), which adopted the term in place of the earlier hyperkinetic-disorder concept. Authoritative reviews summarize its clinical features, genetics, and course. Specific management recommendations are issued by national bodies and lie outside this reference entry.

History

Descriptions of inattentive and overactive children date back over a century, and the disorder was successively labelled minimal brain dysfunction, hyperkinetic reaction, attention deficit disorder, and finally attention-deficit/hyperactivity disorder through evolving DSM editions. The DSM-5 recognized adult ADHD and adjusted symptom criteria, while the ICD-11 aligned its terminology with ADHD, reflecting decades of genetic and neuroimaging research.

Debates

Is ADHD over- or under-diagnosed?

Concerns about variability in prevalence across regions and over time have prompted debate about whether diagnostic thresholds are applied too liberally in some settings and missed in others, particularly in girls and adults; reviews frame this as a question of recognition and criteria rather than of the disorder's validity.

Seminal works

• faraone-2015
• thapar-cooper-2016

Frequently asked questions

Is ADHD only a childhood condition?

No. ADHD begins in childhood, but symptoms or impairment persist into adolescence and adulthood in a considerable proportion of people, and it is now recognized and diagnosed across the lifespan.

What are the main presentations of ADHD?

Standard classifications describe predominantly inattentive, predominantly hyperactive-impulsive, and combined presentations, based on which symptom domain predominates.