ADHD (Attention Deficit Hyperactivity Disorder)

ADHD is a neurodevelopmental disorder characterised by persistent inattention, hyperactivity and impulsivity beyond what is expected for developmental level, present before age 12, evident across multiple settings, and causing genuine functional impairment. The framing that fits the evidence best is executive dysfunction rather than an attention deficit. People with ADHD can concentrate intensely on engaging tasks — hyperfocus is common — and struggle enormously with tasks requiring self-directed effort in the absence of immediate interest or consequence. The impairment is in regulation: initiating, sustaining, shifting and inhibiting, and in the emotional and time-perception systems that depend on the same prefrontal circuitry. Three presentations are recognised: predominantly inattentive, predominantly hyperactive-impulsive, and combined. The inattentive presentation is the most missed, particularly in girls and women, who tend to present with disorganisation, daydreaming, internalised anxiety and chronic underperformance rather than disruptive behaviour. The consequence is a large cohort diagnosed in adulthood, often after a child is assessed. Neurobiologically, ADHD involves dopaminergic and noradrenergic signalling deficits in prefrontal-striatal circuits, with delayed cortical maturation demonstrated on longitudinal imaging. Heritability is around 74%, among the highest of any psychiatric condition. Treatment effect sizes are large. Stimulant medications produce response rates of roughly 70-80%, with effect sizes around 0.8-1.0 — considerably larger than most psychiatric interventions. Behavioural strategies, environmental structure and, for adults, coaching or CBT adapted for ADHD add meaningfully but do not substitute for medication in moderate to severe cases. Untreated ADHD carries real costs: lower educational attainment, higher accident rates, higher substance use, and elevated rates of anxiety and depression.

• •Difficulty starting tasks that require sustained mental effort
• •Losing focus mid-task or mid-conversation
• •Careless errors from inattention rather than lack of understanding
• •Chronic disorganisation and losing essential items
• •Time blindness — consistently misjudging how long things take
• •Restlessness, fidgeting or an internal sense of being driven
• •Interrupting, blurting out, or difficulty waiting
• •Emotional dysregulation and low frustration tolerance
• •Hyperfocus on engaging tasks, to the exclusion of everything else
• •Rejection sensitivity and intense reactions to perceived criticism

• •Genetic factors, with heritability around 74%
• •Delayed maturation of prefrontal cortical circuits
• •Dopaminergic and noradrenergic signalling differences
• •Premature birth and low birth weight
• •Prenatal exposure to alcohol, nicotine or certain toxins
• •Early childhood lead exposure
• •Traumatic brain injury in a minority of cases

ADHD is fundamentally a disorder of the brain circuits underpinning executive function, principally the prefrontal cortex and its connections to the striatum and cerebellum. Longitudinal imaging by Shaw and colleagues showed that cortical maturation in children with ADHD follows a normal trajectory but is delayed by roughly three years, with the greatest delay in prefrontal regions governing attentional control and motor planning. Dopamine and noradrenaline are central. Both are required for optimal prefrontal function, and the relationship is an inverted U — too little or too much impairs performance. Stimulant medication increases synaptic availability of both, which is why it improves function rather than sedating or over-stimulating when correctly dosed. The genetic contribution is polygenic and substantial. Twin studies place heritability around 74%, and hundreds of common variants of small effect have been identified. Environmental factors including prematurity and prenatal exposures contribute but are modest by comparison, and the popular explanations — sugar, screens, poor parenting — are not supported as causes. The delay-aversion model adds explanatory power: people with ADHD show altered reward processing with a steep discounting of delayed rewards, which explains difficulty with tasks whose payoff is distant even when the person fully understands their importance.