How is ADHD diagnosed?
What actually happens in an ADHD assessment — the criteria used, the history taken, what gets ruled out, and why no online questionnaire can replace it.
In short
- There is no blood test, brain scan or single questionnaire that diagnoses ADHD.
- Diagnosis comes from a detailed clinical interview covering your whole history, including childhood.
- Ruling out other explanations is a major part of the process, not an afterthought.
- Rating scales are used as one input among many, never as the decision.
- Who can diagnose, and how you get referred, differs by country — ask your own doctor.
The single most useful thing to understand about ADHD assessment is that it is a clinical judgement built from history, not a measurement. There is no test that returns a result. That is not a gap in the science — it reflects that ADHD is defined by a pattern of functioning over time, which only a history can reveal.
The criteria being applied
Clinicians work from established diagnostic criteria. The details differ slightly between systems, but broadly a diagnosis requires:
- A sufficient number of symptoms from the inattention and/or hyperactivity-impulsivity lists. Typically six or more for children, and five or more for people aged 17 and over — the threshold is lower for adults because some symptoms genuinely diminish with age.
- Persistence — present for at least six months, to a degree beyond what is expected for the person's age.
- Childhood onset — several symptoms present before around age 12, even if never identified at the time.
- More than one setting — for example work and home, or school and home. Difficulty confined to a single environment points elsewhere.
- Clear interference with social, academic or occupational functioning.
- Not better explained by something else. The condition that does most of the work in a careful assessment.
What actually happens in an assessment
A long clinical interview
The core of it. Expect to spend a substantial amount of time — often more than an hour, sometimes across multiple appointments — going through symptoms in detail with concrete examples, how each affects daily life, and your history in each area.
Developmental and childhood history
Because childhood onset is required, this is unavoidable. Clinicians ask about early development, school, behaviour, friendships and whether anyone raised concerns. Useful supporting material includes old school reports, and the recollections of a parent, older sibling or anyone who knew you as a child.
If none of that is available, say so. Clinicians assess adults with no surviving records regularly and work with what exists.
Rating scales
Standardised questionnaires are commonly used — completed by you, and often by a partner, parent or teacher who can describe what they observe. These are genuinely useful for structuring information and comparing against population norms.
What they are not is a diagnosis. A high score prompts further investigation; it does not conclude anything. This is precisely why this site does not host one.
Screening for other explanations
A proper assessment actively considers what else could account for the picture: sleep disorders, anxiety, depression, thyroid problems, iron or B12 deficiency, substance use, hormonal changes, learning difficulties, autism, hearing or vision problems, head injury, and the effects of chronic stress. Some are checked with a blood test.
This is not the clinician being sceptical. It is the most valuable part of the process — several of these are treatable, and getting the wrong answer costs years.
Considering what else may be present alongside
ADHD frequently occurs with other conditions. Identifying them matters for treatment, because managing ADHD alone when significant depression or anxiety is also present tends not to work well.
Impairment and impact
Expect questions about consequences: work history, education, finances, relationships, driving, and health. Symptoms without impairment do not meet the threshold, so the practical effect on your life is a substantive part of the assessment rather than small talk.
What is not used to diagnose ADHD
- Brain scans. Group-level differences exist; they cannot identify an individual. Clinics offering scan-based diagnosis are overstating the science.
- Blood or genetic tests. Bloods may be taken to rule other things out, never to confirm ADHD.
- Computerised attention tests. Sometimes used as supporting information, but not diagnostic on their own.
- Online questionnaires. Useful at most as a prompt to seek assessment.
- A trial of medication. Stimulants improve concentration in most people regardless of whether they have ADHD, so responding well proves nothing.
Who can diagnose it, and how long it takes
This varies enormously between countries, and often between regions within a country. Depending on where you live, ADHD may be diagnosed by psychiatrists, paediatricians, clinical psychologists, specialist nurses, or in some systems by GPs with specific training. Waiting times range from weeks to years, and cost varies from free to substantial.
Because it differs so much, this site does not attempt to describe any particular system. Your own doctor is the person who can tell you what the route is where you live.
On very quick private assessments
Private services can be a reasonable route where public waiting lists are long. It is still worth checking what you are buying: who conducts the assessment and their qualifications, how long it takes, whether childhood history and other explanations are properly explored, and whether your regular doctor will accept the result for ongoing prescribing. A thorough assessment is not a fifteen-minute conversation, and an assessment your health system will not recognise may leave you stuck.
How to prepare
- Write things down beforehand. Specific examples with real consequences are far more useful than "I'm disorganised". Recall under pressure in an appointment is hard for anyone, and particularly hard here.
- Cover the whole timeline. Childhood, school, work, relationships — when each difficulty started and whether it has been continuous.
- Bring documents if you have them. School reports, previous assessments, relevant medical history.
- Bring someone who knows you well, if the service allows it and you are comfortable — an outside perspective is genuinely valuable evidence.
- Be honest about substances, alcohol and sleep. Withholding this makes an accurate answer less likely, not more.
- Mention other conditions you have been diagnosed with, and what treatment did or did not help.
Common questions
What if I am not diagnosed with ADHD?
A thorough assessment that concludes something else is causing your difficulties is a useful outcome, not a failure — particularly if it identifies something treatable. If you disagree with the conclusion, it is reasonable to ask what alternative explanation the clinician reached and why, and to ask about a second opinion.
Can my GP or family doctor diagnose ADHD?
In some countries and systems, yes; in others they refer to a specialist. This is exactly the kind of thing that varies, so ask them directly rather than relying on anything you read online.
Can I be assessed if I have already been diagnosed with something else?
Yes. Existing diagnoses of anxiety, depression, autism or others do not exclude ADHD, and co-occurrence is common. Bring the full history — it helps rather than complicates.
Should I stop my current medication before an assessment?
Do not stop or change any prescribed medication without talking to the prescriber. Ask them what they advise ahead of the appointment.