The DSM-5 diagnostic criteria
ADHD in the UK is diagnosed using the DSM-5 (Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition), published by the American Psychiatric Association. This is the standard most used in UK clinical practice for adult ADHD, and it is the framework that Distinct assessments follow throughout.
For a diagnosis of ADHD in adults, the following conditions must all be met. First, the person must demonstrate a persistent pattern of inattention and/or hyperactivity-impulsivity that interferes with functioning or development. Second, several symptoms must have been present before age 12. Third, symptoms must be present in two or more settings (for example, at work and at home). Fourth, the symptoms must clearly interfere with, or reduce the quality of, social, academic, or occupational functioning. Fifth, the symptoms must not be better explained by another mental disorder.
For adults, the symptom threshold is five or more symptoms from the inattentive domain or five or more from the hyperactive-impulsive domain (compared to six or more for children and adolescents). This adjustment reflects the established finding that symptom counts tend to reduce with age even where impairment remains significant.
The three presentations
DSM-5 defines three presentations of ADHD, which the diagnostic report will specify. Predominantly inattentive presentation: five or more inattentive symptoms are present but fewer than five hyperactive-impulsive symptoms. This is the most common presentation in adults, and particularly in women. Predominantly hyperactive-impulsive presentation: five or more hyperactive-impulsive symptoms are present but fewer than five inattentive symptoms. Combined presentation: five or more symptoms from both domains are present.
The nine inattentive symptoms include: failing to give close attention to details, difficulty sustaining attention on tasks, not listening when spoken to directly, failing to follow through on instructions, difficulty organising tasks and activities, avoiding tasks requiring sustained mental effort, losing items necessary for tasks, being easily distracted by extraneous stimuli, and forgetting daily activities. The nine hyperactive-impulsive symptoms include: fidgeting, leaving seat when remaining seated is expected, running or climbing in inappropriate situations, inability to engage quietly in leisure activities, being "on the go" as if driven by a motor, talking excessively, blurting out answers, difficulty waiting their turn, and interrupting or intruding on others.
How ADHD presents differently in adults
The DSM-5 symptom list was originally developed largely from research on children, and several of the descriptions require interpretation when applied to adults. In adults, hyperactivity rarely manifests as physical restlessness; it is more often experienced as an internal quality of mental restlessness, an inability to switch off, or a need to be constantly occupied or stimulated. Impulsivity in adults often shows up as difficulty waiting, interrupting in conversation, or making decisions without adequate consideration rather than the physical impulsivity of childhood.
Inattentive symptoms in adults frequently express themselves through specific difficulties with sustained effort on unrewarding tasks, working memory lapses, poor time management, difficulty initiating tasks without external pressure, and masking strategies that can make the difficulties less visible but not less real. A skilled clinician assesses these adult expressions of the criteria rather than expecting them to map directly onto child descriptions.
The childhood onset requirement can present a practical challenge for adults who were not assessed as children. The assessment draws on retrospective account rather than contemporaneous records, which is why the DIVA-5 structured interview specifically explores childhood experiences systematically alongside adult ones.
"A diagnosis requires evidence of a persistent pattern across a lifetime, not a particularly difficult day in a consulting room."
The diagnostic tools used
The DIVA-5 (Diagnostic Interview for ADHD in Adults) is the clinical standard for structured assessment of adult ADHD in the UK. It is a semistructured interview that systematically explores each DSM-5 symptom in both childhood and adulthood, with specific examples provided for each to help the person identify whether and how each symptom applies to their experience.
The DIVA-5 is used alongside validated self-report rating scales. The CAARS (Conners Adult ADHD Rating Scales) is the most widely used, providing a standardised measure of current symptom severity. These rating scales provide quantitative data that complements the qualitative information from the clinical interview.
The pre-assessment questionnaire completed before the appointment also contributes structured information that the clinician reviews alongside the interview findings. No single tool is diagnostic in isolation: the clinical conclusion is based on the totality of the evidence gathered, integrated with the clinician's professional judgment.
Differential diagnosis
A thorough adult ADHD assessment considers the differential diagnosis: other conditions that can produce presentations similar to ADHD and that need to be considered before a diagnosis can be made with confidence. This is one of the clinical reasons why assessment by a consultant psychiatrist is significantly more valuable than assessment by a less senior clinician.
Conditions that can present similarly to ADHD, or that frequently co-occur with it, include generalised anxiety disorder, depression, bipolar disorder, autism spectrum conditions, sleep disorders (particularly sleep apnoea), thyroid dysfunction, and, in older adults, early cognitive decline. The clinician's task is not to rule all of these out definitively in a single session, but to consider whether the clinical picture is more consistent with ADHD, with another condition, or with a combination of both.
Where another condition is identified alongside ADHD, the report will address it. Where the presentation suggests something other than ADHD is the primary explanation, the report will say so clearly and set out appropriate recommendations. A well-conducted assessment that concludes ADHD is not present is clinically useful even when it is not the answer the person was hoping for.
Who can diagnose ADHD in the UK
In the UK, a formal ADHD diagnosis can only be made by a specialist clinician: typically a psychiatrist or, for children and young people, a paediatrician. A GP cannot diagnose ADHD, though they play an important role in the referral process and in subsequent shared care prescribing arrangements.
Within private services, assessments are conducted by clinicians of varying seniority, from consultant psychiatrists to mental health nurses and psychologists working under consultant oversight. The clinical authority and the practical usefulness of the resulting report differs significantly depending on who conducts the assessment. For a fuller discussion of this point, see our guide to why the cheapest assessment might be the most expensive mistake.
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NHS versus private diagnosis
The diagnostic criteria and clinical standards are the same whether the assessment takes place on the NHS or privately. The differences are primarily in waiting time, the seniority of the assessing clinician, and the practical usefulness of the report for subsequent purposes.
NHS waiting times for adult ADHD assessment are currently between three and five years in most parts of England. Private assessment is available considerably faster, and a Distinct assessment can typically be arranged within days of booking. For a fuller comparison of the two routes, see our guide to NHS vs private ADHD assessment.
This article has been reviewed for clinical accuracy by Distinct's clinical governance team, led by a consultant psychiatrist and senior NHS clinical leader with over two decades of specialist experience.