ADHD is a neurodevelopmental disorder characterized by persistent patterns of inattention and/or hyperactivity-impulsivity that interfere with functioning or development. It affects approximately 5% of children and 2.5% of adults worldwide. Once considered a childhood-limited condition, ADHD is now recognized to persist into adulthood in 50–70% of cases.

Brain wireframe — ADHD is a neurodevelopmental disorder affecting approximately 5% of children and 2.5% of adults worldwide. Source: Unsplash.

DSM-5 Diagnostic Criteria

Mindfulness nature — ADHD is characterized by persistent inattention, hyperactivity, and impulsivity that interfere with daily functioning. Source: Unsplash.

Inattention (6 or more symptoms for children, 5 for adults age 17+)

Symptoms must persist for at least six months, are developmentally inappropriate, and negatively impact social, academic, or occupational activities. They include: fails to give close attention to details or makes careless mistakes; difficulty sustaining attention in tasks or play; does not seem to listen when spoken to directly; does not follow through on instructions and fails to finish schoolwork or duties; difficulty organizing tasks and activities; avoids or dislikes tasks requiring sustained mental effort; loses things necessary for tasks; easily distracted by extraneous stimuli; forgetful in daily activities.

Hyperactivity and Impulsivity (6 or more symptoms for children, 5 for adults)

Fidgets with or taps hands or feet or squirms in seat; leaves seat in situations when remaining seated is expected; runs about or climbs in situations where it is inappropriate (in adults, restlessness); unable to play or engage in leisure activities quietly; on the go, acting as if driven by a motor; talks excessively; blurts out an answer before a question has been completed; difficulty waiting turn; interrupts or intrudes on others.

Additional Criteria

Several inattentive or hyperactive-impulsive symptoms were present before age 12. Several symptoms are present in two or more settings. There is clear evidence that symptoms interfere with or reduce the quality of social, academic, or occupational functioning. The symptoms do not occur exclusively during the course of schizophrenia or another psychotic disorder and are not better explained by another mental disorder.

Presentations

Combined presentation — both inattention and hyperactivity-impulsivity criteria are met for the past six months. Predominantly inattentive presentation — inattention criteria are met, but hyperactivity-impulsivity criteria are not met. Predominantly hyperactive-impulsive presentation — hyperactivity-impulsivity criteria are met, but inattention criteria are not met. The predominantly inattentive presentation is more common in girls and presents later in life. Hyperactivity tends to diminish with age, while inattention remains more stable.

⚠ Clinical Correlation

In preschool, ADHD presents as excessive motor activity, difficulty sitting still, and poor impulse control. In school-age children, academic underachievement, classroom disruption, and peer difficulties emerge. In adolescence, academic demands exceed attentional capacity, and risky behaviors (substance use, reckless driving) increase. In adults, overt hyperactivity may be replaced by inner restlessness, fidgeting, and difficulty relaxing. Executive function deficits — time management, organization, procrastination, emotional dysregulation — become more prominent in adulthood. Adults with ADHD have higher rates of unemployment, relationship difficulties, divorce, motor vehicle accidents, and substance use disorders. Comorbid conditions include anxiety, depression, substance use disorders, and antisocial behaviors.

Neurobiology

ADHD is highly heritable (70–80% heritability). Candidate genes include DRD4 (dopamine D4 receptor), DAT1 (dopamine transporter), and SNAP25 (involved in neurotransmitter release). The dopamine and norepinephrine systems are central — stimulants block the dopamine transporter (DAT) and norepinephrine transporter (NET), increasing synaptic availability of these neurotransmitters in the prefrontal cortex.

Neuroimaging shows structural differences: reduced total brain volume, slower cortical maturation (particularly in prefrontal regions, delayed by 2–3 years), and reduced volume in the caudate nucleus, putamen, and cerebellum. Functionally, frontostriatal circuits — particularly the prefrontal cortex, anterior cingulate cortex, and striatum — show reduced activation during tasks requiring attention and executive control. The default mode network (DMN) — active during rest and suppressed during tasks — fails to deactivate appropriately in ADHD, leading to mind-wandering and inattention.

Assessment

Diagnosis requires a comprehensive evaluation including clinical interview, developmental history, school or work records, and standardized rating scales (ADHD-RS, Conners scales, SNAP-IV, CAARS for adults). Collateral information from parents, teachers, or partners is essential. Differential diagnosis includes anxiety disorders, mood disorders, learning disorders, autism spectrum disorder, oppositional defiant disorder, and medical causes (thyroid disease, sleep disorders, substance use). Objective measures (continuous performance tests, computerized attention tests) support but do not independently establish the diagnosis.

Evidence-Based Treatment

Pharmacotherapy

Stimulants are first-line, with the largest effect sizes. Methylphenidate (Ritalin, Concerta, Daytrana) blocks DAT and NET. Amphetamine derivatives (Adderall, Vyvanse, Dexedrine) also block DAT and NET and reverse DAT, causing dopamine efflux. Stimulants are available in immediate-release (3–5 hour duration) and extended-release (8–12 hour) formulations. Response rate is 70–80% for the first stimulant tried. Side effects: decreased appetite, insomnia, headache, stomachache, irritability, and, rarely, cardiovascular effects. Growth velocity may be slightly reduced in children; height monitoring is recommended.

Non-stimulants are second-line or used when stimulants are ineffective or poorly tolerated. Atomoxetine is a selective norepinephrine reuptake inhibitor, effective for ADHD but with a smaller effect size and slower onset (4–8 weeks). Alpha-2 agonists (guanfacine extended-release, clonidine extended-release) target prefrontal cortex function and are often used as adjuncts to stimulants or for comorbid tic disorders.

Behavioral Interventions

Behavioral parent training teaches parents to use positive reinforcement, consistent consequences, and environmental structuring to improve child behavior. It is the recommended first-line intervention for preschool-age children.

Behavioral classroom management includes token economies, daily report cards, and teacher-implemented contingencies.

Organizational skills training directly teaches time management, planning, and organization strategies for children and adolescents.

Cognitive behavioral therapy for adult ADHD. Targets executive function deficits and maladaptive beliefs. Includes psychoeducation, behavioral activation, calendar and task management, environmental modification, and cognitive restructuring for procrastination and avoidance.

Educational and workplace accommodations. Extended time on tests, preferential classroom seating, reduced homework load, quiet testing environments, and organizational coaching.

★ Key Concept

Russell Barkleys influential model conceptualizes ADHD as a disorder of executive functioning and behavioral inhibition. Executive functions — working memory (holding and manipulating information), self-regulation of affect and motivation, internalization of speech (self-directed language), and reconstitution (analysis and synthesis of information) — depend on the prefrontal cortex. These functions enable planning, organization, goal-directed behavior, and self-control. In ADHD, impaired inhibition at the root level cascades into deficits in all downstream executive functions. This explains why ADHD is not merely a problem of paying attention but a fundamental impairment in self-regulation that affects every domain of life.

Summary

ADHD is a neurodevelopmental disorder characterized by developmentally inappropriate inattention, hyperactivity, and impulsivity. It is highly heritable and involves dysfunction of frontostriatal dopamine and norepinephrine circuits. Diagnosis requires persistent symptoms across settings with onset before age 12. Stimulant medication is the most effective treatment, with response rates of 70–80%. Behavioral interventions and environmental accommodations are essential components of comprehensive care. ADHD persists into adulthood in the majority of cases and requires ongoing management.