How ADHD is diagnosed: ICD-11 criteria and assessment process

What ADHD is – a neurodevelopmental disorder, not "a lack of effort"

ADHD stands for attention deficit hyperactivity disorder. In ICD-11, this disorder has code 6A05 and belongs to the group of neurodevelopmental disorders – conditions whose onset falls within the period of development and maturation of the nervous system.^[1]

ADHD is a neurodevelopmental disorder, not a simple term for distractedness, laziness or lack of motivation. Its core includes difficulties in sustaining attention, excessive activity and impulsivity – but not every patient presents these symptoms in an identical way. In one child, motor restlessness, interrupting others and difficulty waiting may be most visible; in another – chronic disorganisation, forgetting, losing things and difficulty finishing tasks. In adults, the picture may be less "physical" and more related to organisational chaos, impulsive decision-making, difficulty planning and maintaining a stable routine.^[4]

Placing ADHD among neurodevelopmental disorders has an important clinical consequence: symptoms do not appear suddenly in adulthood. ADHD always begins in childhood; attention deficit hyperactivity disorder cannot first "appear" in adult life. An adult with ADHD did not acquire this disorder – they lived with it earlier, often managing at the cost of considerable effort or with the support of those around them. This text is educational in nature and does not replace specialist assessment.

ICD-11 diagnostic requirements for ADHD

In ICD-11, ADHD has code 6A05 and belongs to the neurodevelopmental disorders. Diagnosis requires a persistent pattern of inattention and/or hyperactivity-impulsivity that directly impairs school, occupational, social or everyday functioning. Symptoms must be stronger than expected for the person's age and level of intellectual development.^[1]

The key requirements are practical as well as formal. Symptoms usually persist for at least six months, begin before age 12, occur in more than one setting and produce real functional difficulty. They must not be better explained by another mental disorder, somatic or neurological condition, sleep disorder, medication effect, substance use, intoxication or withdrawal.^[1]

ICD-11 allows the current clinical presentation to be specified: 6A05.0 predominantly inattentive presentation, 6A05.1 predominantly hyperactive-impulsive presentation and 6A05.2 combined presentation. Other specified and unspecified presentations are also available.^[7]

Absent-mindedness, procrastination or high activity alone is not enough for an ADHD diagnosis. The essentials are childhood onset, persistence, cross-situational symptoms and clear impact on functioning.

How common is ADHD?

ADHD is one of the more common neurodevelopmental disorders. Estimates vary by country, diagnostic criteria and method of study, but systematic reviews indicate that ADHD affects several per cent of children and adolescents. The literature adopts a range of approximately 2–7% of children, with a mean around 5%.^[5,14] In adults, prevalence is lower but still clinically significant – Faraone and colleagues in the World ADHD Federation consensus summary report approximately 2.5% among adults.^[4]

It is worth avoiding two oversimplifications. First, greater recognition of ADHD does not mean every diagnosis is accurate. Second, concern about overdiagnosis should not lead to missing children who genuinely have chronic difficulties with attention, impulsivity and self-regulation.

ADHD in children – symptoms in daily life

In children, ADHD most often becomes visible in situations requiring self-control, waiting, compliance with rules and sustained attention. This is why first difficulties are often noticed in nursery or school: the child does not finish tasks, fidgets, leaves their seat, interrupts others, becomes quickly frustrated, loses equipment, forgets instructions or gives the impression of "not listening" even when they understand what is expected of them.^[2,3]

It is important not to reduce ADHD solely to excessive motor activity, however. Some children – particularly those with predominantly inattentive symptoms – need not be very loud or impulsive. Such a child may be quiet but constantly drifting in thought, have difficulty organising their work, defer tasks, fail to write down information, lose the thread and need many reminders. In clinical practice, this picture is more easily missed, because it does not disrupt the class as visibly as pronounced impulsivity or hyperactivity.

The predominantly inattentive presentation (without marked hyperactivity) is particularly at risk of being missed – especially in girls. The child may be quiet but internally bear a high cost of maintaining apparent control and gradually accumulate academic and emotional failures.

ADHD in young children – when motor activity stops being just a phase

In pre-school children, diagnosis requires particular care, because high activity, impulsivity and a short attention span may be partially age-related. Not every very active child has ADHD. What becomes clinically significant is whether difficulties are clearly greater than in peers, persist across different situations and cause real problems in functioning – for example in relationships with other children, safety, compliance with simple rules or participation in activities.^[3,15]

In this age group, a detailed history from parents and carers and information from the nursery are particularly important. Diagnosis should not rest solely on a single observation in the consulting room, because a child's behaviour can depend greatly on fatigue, anxiety, parenting style, family changes, sleep, temperament or developmental circumstances.

ADHD at school age – organisation, tasks and relationships

At school age, ADHD often manifests through difficulties with organising study, remembering instructions, finishing tasks and impulse control. The child may know the material but not hand in work, make careless errors, not write down homework, interrupt the teacher or have conflicts with peers. From the outside this is sometimes interpreted as lack of effort, immaturity, rudeness or "capable but lazy", when the problem may concern attention regulation, response inhibition and action organisation.^[5,12]

It is also important that academic difficulties need not imply low intelligence. Children with ADHD may have good cognitive capacities and yet fail to manage tasks requiring consistency, planning and independent time management. Assessment should therefore include not only academic results but the way the child works, the level of effort, the degree of frustration, relationships with teachers and functioning at home.

ADHD in girls – a less stereotypical picture

ADHD in girls is often diagnosed later because it more often takes a form that is not disruptive to those around them. A girl with ADHD is not always "unstoppable" or markedly impulsive. She may instead be distracted, chaotic, forgetful, emotionally overloaded, very tired from trying to meet expectations, or perfectionistically masking her difficulties. At school, such a child may not disturb others but internally bear a very high cost of maintaining apparent control.^[10,11]

The stereotype of "ADHD as a hyperactive boy running around the classroom" increases the risk of missing children in whom predominantly inattentive symptoms, disorganisation and emotional overload dominate. In such cases the warning signal may not only be behaviour problems, but also chronic chaos, forgetfulness, difficulty starting tasks, low self-esteem, fear of evaluation and large discrepancies between the child's capacities and their daily functioning.

ADHD in adolescents – symptoms change form

During adolescence the ADHD picture often changes. Hyperactivity may be less visible than in childhood, but difficulties with organisation, planning, emotion regulation, impulsivity and long-term consistency persist. An adolescent may struggle not because they "don't understand" but because they cannot effectively translate intention into action: starting to study, spreading work over time, remembering deadlines, limiting distractions and returning to a task after a break.^[4,8]

In adolescents, risk assessment takes on particular importance: impulsive decisions, conflicts, sleep problems, substance use, lowered self-esteem, anxiety, depressive symptoms and academic overload can complicate the clinical picture. Diagnosis of ADHD in adolescents should therefore encompass not only the question of concentration but also social, emotional, academic and family functioning.^[5]

Estimates of ADHD persistence from childhood into adulthood vary depending on the method of diagnosis and the adopted criteria. It is worth avoiding the overly simple statement that "ADHD always persists for life" or "always passes in childhood."

ADHD in adults – symptoms do not disappear, they just look different

In adults, ADHD often does not look the same as in a child in class. Hyperactivity may take the form of inner tension, difficulty resting, a need for constant stimulation or impulsively switching between activities. Inattentive symptoms more often manifest as lateness, forgetting obligations, difficulty with priorities, deferring tasks, and problems organising documents, finances, work and household responsibilities.^[4,9]

Diagnosing ADHD in an adult requires assessment of the developmental history. The aim is not for the adult to remember every symptom from childhood, but to check whether present difficulties are long-standing, appeared earlier and are not better explained by another problem – depression, anxiety disorder, sleep disorder, substance use, overload or a somatic illness. If attention problems, impulsivity or excessive activity clearly began only in adulthood, other causes should be examined especially carefully, because ADHD as a neurodevelopmental disorder begins in childhood.^[8]

Many adults with ADHD have spent years building compensatory strategies – to-do lists, reminders, working under deadline pressure, choosing highly varied occupations. These strategies can be effective until life demands increase after a job change, the birth of a child or the loss of an external daily structure. At that point ADHD becomes visible – not because it has only just arisen, but because the previous coping methods have ceased to be sufficient.

What can resemble ADHD?

Symptoms similar to ADHD can appear in many situations. Concentration problems can result from anxiety, depression, trauma, sleep disorders, overload, family conflicts, learning difficulties, sensory problems, somatic illness or the action of medications. Hyperactivity and impulsivity can be aggravated by sleep deprivation, stress, irregular daily rhythm, excessive stimulus overload or difficulties in emotion regulation.^[2,3]

An accurate ADHD diagnosis does not consist of simply confirming that a child is inattentive or restless. The key question is whether symptoms are persistent, developmentally inappropriate, present in more than one context and cause clear functional difficulties. It is equally important to check whether another cause does not explain the picture better.

In adults, concentration difficulties, restlessness and impulsivity also belong to the picture of mood disorders, anxiety disorders, stress-related disorders and sleep problems. ICD-11 allows more than one diagnosis in the same person if the picture requires it – determining what is primary and what is co-occurring belongs to the specialist.

ADHD and co-occurring difficulties

In children and adolescents, ADHD can co-occur with oppositional defiant disorder, conduct disorder, specific learning difficulties, anxiety disorders, mood disorders, tics, sleep disorders and autism spectrum disorder (code 6A02).^[12,13] Co-occurrence is not an addition to the diagnosis, but often a key element of the clinical picture, because it affects the child's functioning, the choice of intervention and the prognosis.

Examples of how co-occurrence changes the picture: a child with ADHD and pronounced anxiety may avoid tasks not only because of attention difficulty but also from fear of failure. A child with ADHD and learning difficulties may appear inattentive because the material exceeds their current capacities. A child with ADHD and oppositional features may be seen as "naughty" when what underlies it is difficulty inhibiting responses and regulating emotions.

Similarly in adults, ADHD frequently co-occurs with mood disorders, anxiety disorders and substance use disorders. Sound diagnostics therefore encompasses not only searching for ADHD but also assessing the broader picture and any additional diagnoses.

What does an ADHD assessment look like?

An ADHD diagnosis should not rest on a brief conversation, a scale score or a single observation in the consulting room. NICE states that diagnosis should be based on a full clinical and psychosocial assessment, developmental and psychiatric history, observer reports and mental state assessment.^[2]

The first stage is a detailed interview: what difficulties are present, when they began, how long they have lasted, where they are most visible and how they affect education, work, relationships, home responsibilities and wellbeing. The clinician evaluates frequency, severity, persistence and consequences, not merely whether a behaviour sometimes occurs.

The second stage is reconstructing childhood functioning. In children and adolescents, information from parents and school is important. In adults, school reports, earlier psychological documentation or a conversation with a parent, partner or another person who knew the patient when younger can help. Lack of such information does not always make diagnosis impossible, but it requires more cautious clinical judgement.

The third stage is collecting information across settings. ADHD should be visible in more than one context, such as home and school, university, work or relationships. Symptoms do not have to be equally severe everywhere: they often decrease during highly interesting, urgent or rewarding tasks and increase during routine, sustained mental effort and self-organisation.

The fourth stage is differential diagnosis and assessment of co-occurrence. The specialist checks whether similar difficulties are better explained by anxiety, depression, sleep disorders, trauma, substance use, medical conditions, medication effects, learning difficulties or autism spectrum disorder. In children and adolescents, at least screening for co-occurring emotional, behavioural, developmental and physical problems is recommended.^[3]

Questionnaires and rating scales, such as DIVA-5, are supporting tools. They can organise symptom descriptions and compare the perspectives of the patient, parent, teacher or partner, but they are not a stand-alone diagnostic test. Their results must be interpreted alongside interview data, developmental history, functional impact and differential diagnosis. Therefore, a test score alone is not sufficient to make the diagnosis.^[2]

A useful diagnostic report usually includes not only the diagnostic label, but also the criteria-based rationale, functional description, alternative explanations considered, co-occurring difficulties, the patient's strengths and recommendations for next steps.

What helps after diagnosis?

Support for a child with ADHD should include psychoeducation, environmental adjustment, work with parents, collaboration with the school and – where indicated – pharmacological treatment conducted by an appropriate specialist.^[2,3] For many children, specific, everyday solutions are very important: shorter instructions, dividing tasks into stages, predictable routine, reducing distractions, clear rules, a reminder system, reinforcing positive behaviours and help with organising work.

A child with ADHD usually does not need more pressure alone – they need structure that reduces the cost of self-control. The message "just focus" rarely helps if the problem concerns attention and action regulation. Much more useful are specific instructions: "do the first point now", "put the notebook on the desk", "we'll set a timer for 10 minutes".

For adults, a diagnosis is not a label but a starting point. It makes it possible to understand previous difficulties, relieve unjustified guilt and deliberately choose methods of support – from adjusting the work environment through psychoeducation to methods recommended by a specialist. An accurate diagnosis shifts perspective from evaluative to explanatory.

Summary and when to seek help

ADHD is a neurodevelopmental disorder that always begins in childhood, although it may be recognised only in adolescence or adulthood. This does not mean that the disorder "appeared" in adulthood; it was usually compensated, masked or misinterpreted earlier. Symptoms change form with age – hyperactivity typical of childhood gives way to disorganisation, impulsivity and inner restlessness. The core of the disorder – difficulties with sustaining attention, inhibiting responses and regulating activity – nevertheless remains the same.

An accurate diagnosis requires a comprehensive assessment: history, information from different settings, evaluation of the developmental history and differential diagnosis. The result of a questionnaire, reading an article or comparing oneself with symptoms described online does not replace this.

The content of this guide is educational. If difficulties with attention, organisation or impulsivity persist, escalate or impair daily life – the appropriate step is to arrange a consultation with a specialist, most often a psychiatrist or clinical psychologist. For children, the first contact is often a paediatrician or family doctor who can refer to a specialist clinic.

Frequently asked questions