Attention-deficit hyperactivity disorder

• Attention-deficit/hyperactivity disorder (ADHD) is a chronic neurodevelopmental condition. Its two core dimensions are a persisting problem keeping and organising attention, and/or excessive, poorly controlled motor activity and impulsive action, both present for months and visible in more than one setting.
• It usually begins in childhood, and for most people symptoms and impairment continue into adolescence and adulthood, although the balance of features changes. The current diagnostic systems require some evidence of symptoms before the twelfth birthday.
• There is no blood test, brain scan or single rating scale that diagnoses ADHD. Diagnosis is clinical: a trained specialist weighs a full developmental and psychiatric history, a mental state examination, impairment, and reports from more than one informant and setting.
• For children aged 5 years and over the first-line drug treatment in both NICE NG87 and the AAP 2019 guideline is methylphenidate, with lisdexamfetamine or methylphenidate first-line for adults. Before and alongside medication there is parent training, behavioural support, and school or workplace adjustments. ^[1][2]
• Because ADHD so commonly overlaps with anxiety, depression, oppositional behaviour, learning disorders, tics and autism spectrum disorder, screening for comorbidity is part of the diagnosis, not an afterthought. ^[5]

By the end of this page you should be able to:

1. State the current diagnostic criteria paraphrased in your own words, and name the symptom number needed in each presentation and the age-of-onset and setting rules.
2. Explain the epidemiology of ADHD and why prevalence figures differ between studies.
3. Describe the main genetic, developmental, and environmental risk factors, and the brain circuits and neurotransmitters implicated.
4. Carry out a clinical assessment of ADHD in a child, adolescent or adult, including history, mental state examination, risk assessment and comorbidity screening.
5. Distinguish ADHD from the conditions that commonly mimic or accompany it.
6. Choose and explain first-line non-pharmacological and pharmacological treatments, and give typical starting and maximum doses for the main drugs.
7. Plan baseline checks, titration, and the long-term monitoring of pulse, blood pressure, height and weight.
8. Counsel families about course, complications, driving, and transition to adult services.

The two symptom dimensions are inattention (difficulty sustaining attention, disorganisation, forgetfulness, avoiding sustained mental effort, being easily distracted) and hyperactivity-impulsivity (fidgeting, leaving one's seat, running or climbing inappropriately, excessive talking, difficulty waiting turns, interrupting). From these dimensions three clinical presentations are recognised. The predominantly inattentive presentation is the one most often seen in girls and in adults. The predominantly hyperactive-impulsive presentation is more common in very young children. The combined presentation is the one most often associated with functional impairment in childhood. A presentation can change over the lifespan even though the person remains the same individual. ^[3]

ADHD is not a personality flaw or the result of poor parenting. It is best understood as a spectrum condition that shades into normal variation, which is exactly why thresholds, settings and impairment matter as much as the symptoms themselves. ^[3][4]

Estimates vary with the criteria, the age group, and whether cases are drawn from community or clinical samples, so a single "true" prevalence does not exist. The American Psychiatric Association (APA) estimates that 8.4% of children and 2.5% of adults have ADHD. ^[3] A meta-analysis cited by the American Academy of Pediatrics (AAP) 2019 guideline gives a pooled worldwide prevalence of 7.2% among children, with some community-based samples reporting between 8.7% and 15.5%. ^[2] The Canadian Paediatric Society (CPS), quoting a 2018 review, estimates that ADHD affects about 3.4% of children and youth worldwide and describes it as the third most common mental health disorder after depression and anxiety. ^[4] Boys are diagnosed more than twice as often as girls, although the true sex ratio is smaller than the diagnosed ratio, because inattentive and less disruptive presentations are missed. ^[2][3] In one US national survey 9.4% of children aged 2 to 17 years had ever had an ADHD diagnosis and 8.4% currently had the condition, representing about 5.4 million children, with a median age of diagnosis of 7 years. ^[2]

ADHD is chronic: most children continue to have symptoms and impairment through adolescence and into adulthood. The AAP notes that overt hyperactive and impulsive symptoms tend to decline with age while inattentive symptoms persist. ^[2] The CPS estimates that 50% of children with ADHD continue to have symptoms of ADHD in adolescence and adulthood. ^[4] ADHD is under-recognised in girls and women, who are less likely to be referred and more likely to be given another, incorrect, diagnosis. ^[1]

The strongest risk factor is inheritance: twin and family studies show high heritability, although no single gene accounts for it, and the family pattern also reflects shared environment. ^[4] Having a close relative with ADHD increases the chance markedly. ^[1]

Other consistent risk factors include:

• prenatal exposure to alcohol or tobacco, and low birth weight below 2500 g, both of which carry strong evidence of increased ADHD risk; ^[4]
• being born preterm, which NICE singles out as a group with increased prevalence; ^[1]
• being the youngest in a school year (relative immaturity masquerading as a disorder); ^[2]
• psychosocial adversity and looked-after children; ^[1]
• co-occurring neurodevelopmental disorders such as autism spectrum disorder or intellectual disability, and conditions such as epilepsy. ^[1]

Neurobiologically, imaging and neuropsychological work point to a developmental disorder of fronto-striatal and fronto-cerebellar circuits involving the prefrontal cortex, basal ganglia, anterior cingulate cortex and cerebellum. These circuits depend on dopaminergic and noradrenergic signalling, and the parts that are delayed most in structural development are those supporting attention, working memory and impulse control. ^[4] This is why stimulants, which increase synaptic dopamine and noradrenaline, help. ^[3][9]

ADHD is thought of as a disorder of self-regulation rather than of energy alone. Dopamine and noradrenaline modulate signalling in the circuits above; when they are dynamically poorly regulated, sustaining attention, resisting distraction and inhibiting a prepotent response all become harder. ^[3][4] The result is not a single symptom but a trait that leaks out in different situations: a child may focus for an hour on a favourite video game (high intrinsic reward, no delay) and fall apart doing homework; an adult may hyperfocus under deadline pressure and miss routine social cues.

As individuals grow older, overt hyperactivity tends to be internalised as restlessness, and impulsive actions give way to impulsive decisions, mood lability and poor time management. Sleep disturbance, which is common in ADHD, both worsens and resembles the cognitive deficits. ^[1][2]

A careful history is the diagnosis. Ask separately about inattention and hyperactivity-impulsivity, and in each case ask for concrete examples rather than labels. "He never finishes anything" is a conclusion; "he starts homework, leaves his desk three times, loses the book, and gets a detention for shouting out an answer" is evidence.

Common parent or self descriptions include:

• cannot sustain attention in class or meetings, loses things, makes careless mistakes, avoids tasks that demand sustained thought, is forgetful in daily activities; ^[3]
• fidgets, leaves his seat, runs about when sitting is expected, talks excessively, cannot wait his turn, interrupts others; ^[3]
• difficulty organising tasks, poor time estimation, and emotional volatility after trivial frustration.

The history must cover duration (problems for at least six months), impairment (at least moderate psychological, social, academic or occupational impairment), and pervasiveness (two or more important settings). ^[1] NICE recommends taking children's and young people's views into account when deciding whether impairment is clinically significant. ^[1] In adults, retrospective childhood information is essential, because diagnosis requires that some manifestations began before the twelfth birthday. ^[1][3]

Ask also about sleep, substance use (which both mimics and complicates ADHD, and which NICE and AAP flag as a prominent risk in adolescents), traffic accidents, financial mishaps, relationship conflict, and whether the person drives or operates machinery. ^[1][2]

There is often no abnormal physical sign, and a normal examination never excludes ADHD. Look for tics, clumsiness (developmental coordination disorder is commonly comorbid), growth parameters, blood pressure and pulse (a baseline for later monitoring), and any medical mimic such as thyroid disease or sensory impairment. ^[1]

Observe the interview itself. The person may arrive late, ramble, interrupt, and struggle to sit still; or they may hide all of this, particularly if they are bright and anxious, so absence of visible restlessness does not rule the diagnosis out. ^[3]

Risk assessment is mandatory: ask about self-harm and suicide (adolescents with ADHD have increased risk), risky sexual behaviour, aggression, and diversion of prescribed stimulants. NICE also notes that ADHD may affect driving, and that people in the UK must declare their diagnosis to the Driver and Vehicle Licensing Agency if symptoms or medication affect safe driving. ^[1]

• Preschool (4 to 6 years). Symptoms are present but hard to separate from normal toddler behaviour; evaluation relies heavily on parent and teacher report, and parent training is the first treatment even before a firm diagnosis. ^{[2] [1]}
• School age. Hyperactive and impulsive features dominate and create most impairment; median age of diagnosis is about 7 years. ^[2]
• Adolescence. Overt hyperactivity decreases, inattention persists, and mood and anxiety disorders, risky behaviour, and substance use become more prominent. ^[2]
• Adulthood. Disorganisation, poor planning, restlessness and impulsivity dominate; adults may present with job loss, university failure, or relationship problems rather than with behavioural complaints. ^[3]

Many problems produce or mimic inattention, and several commonly coexist with ADHD. The CPS lists conditions that are commonly misdiagnosed as ADHD, in decreasing frequency: learning disorder, sleep disorder, oppositional defiant disorder, anxiety disorder, intellectual disability, language disorder, mood disorder, tic disorder, conduct disorder, autism spectrum disorder, and developmental coordination disorder. ^[4] The APA adds thyroid disease, head injury, substance use and mood disorders. ^[3] Distinguish ADHD by its developmental early onset, its breadth across settings, and the absence of an episodic pattern that would suggest mood or another primary disorder. ^[9]

No medical test diagnoses ADHD. Routine blood tests, liver function tests and electrocardiograms are not needed in people taking ADHD medication unless there is a clinical indication, in NICE's words. ^[1] NICE and the AAP agree that the diagnosis is made by a clinician with training and expertise, using a full clinical and psychosocial assessment, a full developmental and psychiatric history, and observer reports with a mental state examination. ^[1][2] Rating scales such as the Conners scales and the Strengths and Difficulties Questionnaire are helpful additions, but a diagnosis should not be made on rating-scale or observational data alone. ^[1] For those aged 6 to 17 years, NICE allows QbTest, a computerised continuous performance test with movement tracking, as an adjunct to support diagnosis. ^[1]

Clinically useful baseline checks before medication are carried out during the baseline assessment: full medical history, current medication, height and weight plotted against normal ranges, pulse and blood pressure with an appropriately sized cuff, and a cardiovascular assessment, referring for cardiology opinion if there are red-flag cardiac features or consistently raised blood pressure. ^[1] Neuropsychological or imaging tests are not needed for typical cases, though cognitive assessment can clarify learning strengths and weaknesses. ^[2]

The table summarises the thresholds a clinician applies; these are the DSM-5-TR criteria as represented in the guidelines, written in original words rather than copied from the manual. ^[2][3]

NICE states the equivalent criteria using ICD hyperkinetic disorder language: symptoms meeting diagnostic criteria that cause at least moderate impairment and happen often in two or more important settings. ^[1]

Screening for comorbidity is required at diagnosis. The AAP lists emotional or behavioural conditions (anxiety, depression, oppositional defiant disorder, conduct disorder, substance use), developmental conditions (learning and language disorders, autism spectrum disorder) and physical conditions (tics, sleep apnoea). ^[2] NICE adds intellectual disability, epilepsy, specific learning difficulties and other neurodevelopmental disorders to the list of groups with increased prevalence, and requires assessment of social, familial, educational and occupational circumstances and physical health. ^[1] In the CPS position statements, oppositional defiant or conduct disorder co-occurs in up to 90% of cases, anxiety disorders in about 30%, and specific learning disorder in about one-third; ADHD prevalence is three to four times higher in children with intellectual disability. ^[4]

Because a substantial proportion of children with ADHD are also on the autism spectrum, and the reverse is true, the Canadian guidance (CPS Part 3) confirms that stimulants remain the first-line pharmacological treatment for ADHD co-existing with autism or intellectual disability, while warning that non-response and side effects, especially irritability with emotional outbursts, are more common in this group. ^[5]

Build a holistic shared treatment plan addressing psychological, behavioural, occupational and educational needs, with the person and family involved in decisions that can be revisited. ^[1] Environmental modification comes before drugs: advise on a balanced diet, activity, regular exercise, consistent routines, clear rules, and positive parent-child contact. ^[1] NICE recommends an ADHD-focused group parent-training programme for children under 5 as first-line treatment. ^[1] Behavioural support and educational adjustment are part of the plan at every age, not optional extras. ^[2]

Medication is offered when symptoms remain significantly impairing after environmental modifications have been implemented and reviewed, and when a baseline assessment has been completed. ^[1] Drugs are never a complete service: NICE recommends adding a course of cognitive behavioural therapy (CBT) for young people who have benefited from medication but still have significant impairment, and structured supportive psychological intervention with ADHD focus, often including CBT, for adults. ^[1]

For preschool-aged children (from the fourth birthday to the sixth birthday), the first-line treatment is parent training in behaviour management (PTBM) and/or behavioural classroom interventions, with NICE recommending an ADHD-focused group parent programme. ^[1][2] Medication, usually methylphenidate, may be considered if these behavioural interventions do not produce significant improvement and there is moderate to severe continued disturbance in functioning, and only after a second specialist opinion. ^[1][2] Clinicians do not need an ADHD diagnosis before recommending parent training, because it helps a wide range of problem behaviours. ^[2]

NICE offers methylphenidate (short or long acting) as the first-line drug for children aged 5 years and over and young people with ADHD. ^[1] The AAP equivalent is Key Action Statement 5b and 5c: for children from age 6 to the twelfth birthday, FDA-approved medication along with parent training and/or behavioural classroom intervention (preferably both); for adolescents from 12 to 18 years, medication with the adolescent's assent plus encouraged behavioural or training interventions. ^[2] If methylphenidate is insufficient after a six-week trial at adequate dose, lisdexamfetamine is considered next; dexamfetamine is an option where responding to lisdexamfetamine but intolerant of its longer effect profile. ^[1] If stimulants are not tolerated or effective, atomoxetine or guanfacine are offered. ^{[1] [3]}

Typical titration is low start, increase gradually (usually weekly), recording symptoms, impairment and adverse effects at baseline and at each dose change, reviewing regularly such as by weekly telephone contact during titration. ^[1][6] Drugs are titrated to the maximum benefit with tolerable side effects. ^[2]

A few drug details deserve emphasis:

• Take methylphenidate at the same time each day and aim to standardise whether it is taken with food; different brands release differently. ^[6]
• Atomoxetine needs six weeks or more to show benefit and acts through noradrenaline reuptake inhibition; it can be stopped without tapering but monitor for mood changes. ^[9]
• Guanfacine, an alpha-2A agonist, can cause somnolence, hypotension and bradycardia and must be withdrawn slowly to avoid rebound rises in blood pressure and heart rate. ^[8]
• Clonidine, the other alpha-agonist, is FDA-approved in the USA but is not in NICE's recommended list; regional guidance varies. ^[3]

NICE offers lisdexamfetamine or methylphenidate as first-line pharmacological treatment for adults with ADHD. ^[1] Atomoxetine is offered if lisdexamfetamine or methylphenidate is not tolerated or has failed after separate six-week trials. ^[1] Non-pharmacological treatment is indicated for adults who have chosen not to take medication, who cannot tolerate or adhere to it, or who have benefited from medication but still have impairment: at minimum a structured supportive psychological intervention with ADHD focus, regular follow-up, and often CBT. ^[1]

Baseline assessment and physical health review are the same as for younger patients: confirm the diagnosis still holds, review mental health, social circumstances, substance misuse and diversion risk, and carry out a physical review with height, weight, pulse, blood pressure and cardiovascular assessment. ^[1]

Monitoring is where harm is prevented. NICE specifies: ^[1]

• measure height every 6 months in children and young people; ^[1]
• measure weight every 3 months in children aged 10 years and under, and in children over 10 years at 3 and 6 months and every 6 months thereafter; ^[1]
• measure weight every 6 months in adults; ^[1]
• monitor heart rate and blood pressure, and compare with the normal range for age, before and after each dose change and every 6 months; ^[1]
• monitor body mass index in adults if weight changes.

In addition, do not offer routine blood tests (including liver function tests) or ECGs to people taking ADHD medication unless there is a clinical indication. ^[1] However, NICE also requires referral for cardiology assessment before starting medication where there is a history or signs suggestive of cardiac disease, and referral to a paediatric hypertension specialist if blood pressure is consistently above the 95th centile for age and height in children. ^[1]

Compare blood pressure to the appropriate normal range for age; if there is sustained resting tachycardia above 120 beats per minute, an arrhythmia, or systolic blood pressure above the 95th percentile (or consistently hypertensive in adults), reduce the dose and refer. ^[1] NICE does not recommend routine laboratory monitoring; local cardiac precautions still apply. ^[1]

Review medication before and after school transitions: a formal reassessment at school-leaving age, usually completed by age 18, supports transition to adult services, with the care programme approach used from age 16. ^[1]

Left untreated or undertreated, ADHD impairs functioning across life domains. Academic and occupational underachievement, accidents and injuries, substance misuse (particularly in adolescence), anxiety and depression, and impaired social relationships are common. ^[1][2][4] The divergence between early ability and later achievement can damage self-esteem, and adults may develop compensatory coping that fails under stress. ^[3] Financial and legal difficulties occur more often than in the general population. ^[1] Driving safety is affected by impulsivity and may improve with treatment; adolescents should be counselled about this. ^[1]

Medication adverse effects, managed by titration and monitoring, include appetite suppression and weight loss, sleep disturbance, headache, abdominal pain, and, rarely, cardiovascular effects. ^[6][8] Stimulants are controlled drugs and require secure storage, patient identity checks, and awareness of misuse and diversion. ^[6]

The prognosis is good when the diagnosis is made early and treatment combines pharmacological, behavioural and educational approaches. ^[2][4] Symptom severity fluctuates: overt hyperactivity usually declines with age, while inattention and executive dysfunction tend to persist. ^[2] NICE advises reassessing need for continuing treatment and considering de-challenge to test whether symptoms persist, while monitoring for relapse for at least two years after withdrawal. ^[1] No cure exists; ADHD is a long-term condition, but most people develop a workable strategy with the right support. ^[3][4]

There is no proven way to prevent ADHD, although reducing known risk exposures (maternal smoking and alcohol in pregnancy, preterm birth prevention, and timely treatment of hearing and vision disorders) is reasonable. ^[4] NICE explicitly recommends that universal screening for ADHD should not be undertaken in nursery, primary or secondary schools. ^[1] Screening should be targeted: identifying children with behavioural and attention problems and applying the evaluation pathway when impairment is significant. ^[1][2] The separate MedGrasp topic "Autism spectrum disorder, ADHD and developmental delay" outlines red flags and screening tools for children; this topic supplies the full criteria and management framework for the disorder itself. A child's ADHD is more likely to be detected when teachers and parents know what to look for and the clinician can arrange a formal assessment. ^[2]

For children aged 4 to 6, parent training is the first-line treatment; medication is reserved for moderate to severe continued disturbance after behavioural approaches, with a second specialist opinion, and benefits from NICE's watchful waiting of up to 10 weeks where impairment is moderate rather than severe. ^[1][2] Diagnosing in this age group is challenging because multi-setting observation is harder if the child does not attend nursery or childcare. ^[2]

Adolescents may need information from two teachers or other sources outside the family. They often under-report their own symptoms. The risks of mood and anxiety disorders, self-harm, risky sexual behaviour and substance use rise in this age group, and marijuana in particular can mimic ADHD. Clinicians must establish that some ADHD manifestations existed before age 12. ^[2] Check contraception, driving advice and appropriate autonomy in treatment decisions. ^{[1][2] [3]}

The NHS Scotland general guidance states that no medications for the treatment of ADHD are recommended in pregnancy or breastfeeding, referring prescribers to individual summaries of product characteristics and the BUMPS service. ^[2] This is a caution, not a blanket prohibition forever: if a woman plans pregnancy, the decision to continue, switch or stop medication should be made before conception with the specialist, the woman and, where relevant, the obstetric team, weighing maternal functioning and impairment against fetal exposure. ^{[1] [8]} Evidence on stimulant use in pregnancy is limited and should be checked against current product information. ^[8]

ADHD persists into older age, although less is known about it. The diagnostic principles are unchanged: symptoms from childhood, impairment in two settings, and exclusion of other causes including cognitive decline, mood disorder and medication effects. Cardiovascular disease becomes more prevalent, so baseline and monitoring blood pressure and pulse are particularly important, and stimulant doses are often lower. ^[1]

ADHD with autism spectrum disorder or intellectual disability is common. The CPS confirms that psychostimulants should be first-line pharmacological treatment in children diagnosed with both autism and ADHD, with the expectation of higher rates of non-response and adverse effects, especially irritability with emotional outbursts. ^[5] For ADHD in intellectual disability, prevalence is three to four times the general rate and stimulants are used first when medication is needed. ^[5] NICE recommends offering the same medication choices to people with ADHD and anxiety disorder, tic disorder or autism spectrum disorder as to other people with ADHD. ^{[1] [3]}

Where specialist teams, rating scales and continuity of care are limited, a few measures preserve quality: use a structured history and a single page describing symptoms across home and school; rely on teacher and parent report even from informal interviews; and treat ADHD with the cheapest effective preparation available, usually immediate-release methylphenidate, starting low and titrating to effect. ^[6][10] Parent training can be delivered in groups, in schools or by telephone and needs no credential beyond being taught the skills. ^[1][2] Where ECGs and routine laboratory tests are not indicated anyway, scarce resources are better spent on blood pressure cuffs, growth charts and follow-up. ^[1] Refer when the diagnosis is uncertain, when comorbidity is significant, or when the child is under 5 and medication is being considered. ^[1][2]

• ADHD is a chronic neurodevelopmental disorder with two core dimensions, inattention and hyperactivity-impulsivity, previously treated as separate disorders.
• Diagnosis requires symptom counts of six or more, or five or more in people 17 and older, in at least one dimension, plus onset before age 12, duration of at least six months, impairment in two or more settings, and exclusion of better explanations.
• Prevalence estimates range from about 3.4% to 8.4% in children depending on criteria and source; boys are diagnosed more than twice as often as girls, though inattention in girls is under-recognised.
• Genetics dominate the aetiology, with heritability of 70 to 80%; prenatal exposures and preterm birth add risk.
• Brain circuits dependent on dopamine and noradrenaline, particularly fronto-striatal and fronto-cerebellar pathways, mature later in ADHD.
• No medical test diagnoses the condition; clinicians combine history, mental state examination, functional impairment and multi-informant report.
• Always screen for comorbid anxiety, depression, oppositional defiant or conduct disorder, tics, sleep apnoea, learning and language disorders, autism spectrum disorder and substance use.
• For children aged 5 years and over, first-line medication is methylphenidate; lisdexamfetamine follows if needed, then atomoxetine or guanfacine.
• For adults, first-line medication is lisdexamfetamine or methylphenidate; non-pharmacological treatment is essential for those not taking medication or with residual impairment.
• Before starting medication, complete a baseline physical assessment and refer when cardiac red flags or hypertension are present.
• Monitor height every 6 months, weight 3 or 6 monthly by age, and pulse and blood pressure at dose changes and every 6 months; do not order routine ECGs or liver tests.
• Preschool children receive parent training first; medication only with a second specialist opinion.
• ADHD persists into adulthood in roughly half to two-thirds of cases, and cognitive rather than hyperactive features dominate later life.
• Composite care including school and employer adjustment, behavioural therapy and medication yields the best outcomes.
• NICE NG87 and the AAP 2019 guideline agree on methylphenidate first in children and multi-modal care, while differing in details; both encourage shared, revisitable treatment plans.
• Special groups needing tailored care include pregnant women (no ADHD medication recommended routinely), adolescents with high-risk behaviour, and older adults with cardiovascular disease.

• Autism spectrum disorder, ADHD and developmental delay (MedGrasp, pediatrics): red flags, screening, and the combined evaluation of neurodevelopmental disorders in children.
• Antipsychotics and adverse effects (MedGrasp): useful background on monitoring and pharmacological cautions relevant to comorbid mental health care.
• Alzheimer disease and dementia (MedGrasp): an example of how cognitive impairment in later life is separated from lifelong attention problems.