Adult ADHD assessment is one of the fastest-growing areas of clinical work in the UK. Referrals have multiplied, waiting lists for an NHS ADHD assessment run to years in many areas, and Right to Choose has brought a wave of private and independent providers into the pathway. With that volume comes scrutiny: an adult ADHD diagnosis is increasingly questioned by GPs asked to take on shared care, by employers, and by patients themselves. This guide sets out what a defensible adult ADHD assessment involves, which tools to use, and where the common errors lie.
How common is adult ADHD?
ADHD persists into adulthood in a majority of those diagnosed as children, and an estimated 2.5–4% of adults meet criteria worldwide. In the UK most of them are undiagnosed. Under-recognition is greatest in women, in older adults, and in people whose presentation is predominantly inattentive rather than hyperactive — the ones who were never disruptive enough to be referred at school. Many arrive for assessment in their thirties and forties after years of treatment for anxiety or depression that never quite worked.
What an adult ADHD assessment involves
There is no single test for ADHD. A gold-standard assessment triangulates several sources of evidence: a structured clinical interview covering current symptoms, developmental history and functional impairment across more than one setting; validated rating scales; collateral information from someone who knew the patient as a child or knows them well now; and a systematic screen for co-occurring and alternative conditions. NICE guideline NG87 expects the diagnosis to be made by a psychiatrist, paediatrician or another appropriately qualified healthcare professional with training and expertise in ADHD, on the basis of a full clinical and psychosocial assessment — not on a questionnaire score.
Which ADHD rating scales and interviews to use
The Adult ADHD Self-Report Scale (ASRS-v1.1) is the standard screening tool: quick, free and well validated, but a screen rather than a diagnosis. For the diagnostic interview, the DIVA-5 (Diagnostic Interview for ADHD in Adults) and the ACE+ are the most widely used structured instruments in UK practice; both walk through each DSM-5 criterion in childhood and adulthood with concrete examples, which is what makes the resulting diagnosis reproducible. The Conners' Adult ADHD Rating Scales (CAARS) and the Brown scales add informant versions and symptom-domain profiles. Whichever you use, record the instrument, the scores and the reasoning — a diagnosis that cannot be reconstructed from the notes is hard to defend.
Establishing childhood onset
DSM-5 requires several symptoms to have been present before the age of 12. Retrospective self-report is the weakest part of most adult assessments: people under-report because they assumed everyone found school that hard, or over-report after reading about ADHD. School reports are the most useful objective record and are worth asking for explicitly — 'could do better', 'easily distracted', 'chatty', 'careless mistakes' are the phrases to look for. A parent, older sibling or long-term partner interviewed briefly, with consent, adds more than any scale.
Differential diagnosis and co-occurring conditions
Differential diagnosis is the most demanding part of ADHD assessment. Generalised anxiety, depression, bipolar II disorder, emotionally unstable personality disorder, autism, sleep disorders, substance use and thyroid disease can each mimic ADHD, and several of them commonly co-occur with it. The distinction usually lies in the timeline: ADHD is lifelong and pervasive, whereas mood and anxiety symptoms are episodic and often secondary. Screen for autism in every adult ADHD assessment; the overlap is large and both are under-recognised, particularly in women. Screen too for the consequences of untreated ADHD — substance misuse, eating disorders, dangerous driving, financial difficulty — because they shape the risk assessment and the treatment plan.
Is neuropsychological testing needed?
No. Cognitive testing is not required for an ADHD diagnosis and does not reliably distinguish ADHD from its absence at the individual level: many adults with clear ADHD perform normally in a quiet testing room. It can be useful for clarifying a specific profile — a suspected learning disability, a query about acquired brain injury — but it should not be the basis of the diagnosis, and its absence should never be a reason to withhold one.
Baseline checks before medication
If medication is being considered, NG87 expects a cardiovascular history including family history of sudden cardiac death, baseline blood pressure and heart rate, weight (and height in anyone still growing), a medication review for interactions, and an ECG where the history indicates one. These belong in the assessment, not in a later appointment, because they determine whether treatment can start and whether the case will be acceptable for shared care with the GP.
Shared decision-making
The assessment ends with a conversation, not a letter. Explain what the diagnosis means and what it does not, the evidence for medication and for psychosocial treatment — psychoeducation, ADHD coaching, CBT-based approaches — and what monitoring involves. Many patients describe the explanation of their own neurobiology as the most therapeutic part of the process. Document the discussion; it is part of a defensible assessment.
Training in adult ADHD assessment
Clinicians moving into ADHD work — psychiatrists, GPs with a special interest, nurse and pharmacist prescribers, clinical psychologists — increasingly want structured CPD rather than learning under pressure. Mind Companion Institute's Adult ADHD Assessment Course is a CPD-accredited programme built by practising clinicians that takes the assessment from referral to diagnosis and treatment planning, with the tools, differentials and documentation covered in the depth a busy service needs.