What Is ADHD? Types, Causes and How It’s Diagnosed

In short: ADHD (Attention-Deficit/Hyperactivity Disorder) is a common neurodevelopmental condition that affects attention, impulse control and activity levels. It comes in three presentations — inattentive, hyperactive-impulsive, and combined — and is caused mainly by genetic and neurological differences in how the brain uses dopamine and noradrenaline. It affects roughly 2.5–4% of adults.¹²

What is ADHD?

ADHD is a neurodevelopmental condition characterised by persistent patterns of inattention and/or hyperactivity-impulsivity that interfere with daily functioning. It is not a matter of laziness, low intelligence or poor discipline — it reflects real differences in brain structure and chemistry, particularly in the systems that regulate attention, motivation and self-control.

What does ADHD stand for?

ADHD stands for attention deficit hyperactivity disorder — written attention-deficit/hyperactivity disorder in the DSM-5, the diagnostic manual clinicians use. healthdirect, the Australian Government’s health information service, describes it as a neurodevelopmental (brain development) condition that begins in early childhood, and estimates that around 1 in 20 people in Australia has ADHD.³ See how common ADHD is in Australia.

The three types (presentations) of ADHD

The DSM-5 describes three presentations, because symptoms can shift over a person’s life:

• Predominantly Inattentive — mainly difficulty focusing, forgetfulness, disorganisation and losing things. Often called “ADD” and frequently missed, especially in women.
• Predominantly Hyperactive-Impulsive — mainly restlessness, fidgeting, impulsivity and interrupting. More visible, and more often identified in childhood.
• Combined Presentation — significant symptoms of both. This is the most commonly diagnosed presentation in adults.

ADD vs ADHD: what’s the difference?

“ADD” (Attention Deficit Disorder) is an older term. It is no longer used clinically — what people call ADD is now the predominantly inattentive presentation of ADHD. So ADD and ADHD are not separate conditions; ADD is simply an outdated name for one type of ADHD.

What causes ADHD?

ADHD is one of the most heritable conditions in psychiatry — genetics account for a large share of the risk, which is why it often runs in families. The Australian ADHD Guideline estimates heritability at 70–80%.⁴ Differences in how the brain uses dopamine and noradrenaline affect the executive-function networks that manage attention and impulse control. ADHD is not caused by parenting style,⁵ and there’s no evidence it’s caused by particular foods such as additives,⁶ though sleep, diet and stress can affect how symptoms show up day to day. Read more in is ADHD genetic?

What is ADHD in adults?

Many children diagnosed with ADHD still have symptoms as adults, and ADHD can also be diagnosed for the first time in adulthood.³ About 7 in 10 children with ADHD continue to experience symptoms as adults.⁷ Adults are more likely to keep inattention symptoms than obvious hyperactivity,⁴ so adult ADHD often looks like careless mistakes at work, difficulty sustaining attention and organising tasks, losing things, forgetfulness, feeling restless or driven to stay busy, interrupting, rapid changes in mood and sleep difficulties.⁷

See ADHD symptoms in adults and does ADHD get worse with age?

How is ADHD diagnosed in adults?

Adult ADHD is diagnosed against DSM-5 criteria: five or more symptoms of inattention and/or hyperactivity-impulsivity, present for at least six months, with several present before age 12, causing impairment in more than one setting, and not better explained by another condition. Assessment uses validated questionnaires, your history and collateral information. Depending on your state, a psychiatrist, a paediatrician or a GP who meets the state’s requirements can make the diagnosis — see who can diagnose ADHD in Australia and how to get diagnosed.

Is ADHD a mental illness?

ADHD is classified in the DSM-5 as a neurodevelopmental disorder, alongside other mental disorders, but it differs from conditions such as depression in that it begins in childhood and relates to how the brain develops.⁴ It is also covered by the definition of disability in the Disability Discrimination Act 1992.⁸ Read more in is ADHD a mental illness?

Frequently asked questions

What does ADHD stand for?

ADHD stands for attention deficit hyperactivity disorder (attention-deficit/hyperactivity disorder in the DSM-5). It is a neurodevelopmental condition that begins in childhood.

What are the three types of ADHD?

Predominantly inattentive, predominantly hyperactive-impulsive, and combined presentation. The type is based on which symptoms are most prominent, and it can change over time.

Is ADD the same as ADHD?

Yes — ADD is an outdated term for what is now called the predominantly inattentive presentation of ADHD. They are not separate conditions.

What causes ADHD?

Mainly genetic and neurological factors affecting how the brain uses dopamine and noradrenaline. It is highly heritable and often runs in families. It is not caused by parenting style or by food additives.

Is ADHD a mental illness or a disability?

ADHD is a neurodevelopmental condition. It is classified in the DSM-5 alongside other mental disorders, and it is covered by the definition of disability in the Disability Discrimination Act 1992, which gives protection from discrimination and a right to reasonable adjustments.

This article is general information only and is not medical advice. Only a qualified health professional can diagnose ADHD. ADHD GP is a private telehealth clinic staffed by AHPRA-registered Australian GPs.

Next steps

Not sure whether you have ADHD? Take our free ADHD test — the full 18-question ASRS self-assessment with instant scoring — to see whether your symptoms warrant a formal assessment.

If ADHD might be affecting you, our GPs offer telehealth assessments for adults in Queensland — no referral needed — and we’re working on opening in other states. Book an assessment, see how it works, or compare your ADHD assessment options in Queensland.

Related reading: Inattentive ADHD in adults, ADHD and autism (AuDHD) and is ADHD genetic?

References

1. Simon V, Czobor P, Bálint S, Mészáros Á, Bitter I. Prevalence and correlates of adult attention-deficit hyperactivity disorder: meta-analysis. British Journal of Psychiatry. 2009. PubMed PMID 19252145 — Pooled prevalence of adult ADHD 2.5% (95% CI 2.1–3.1).
2. Kessler RC, Adler L, Barkley R, et al. The prevalence and correlates of adult ADHD in the United States: results from the National Comorbidity Survey Replication. American Journal of Psychiatry. 2006. PubMed PMID 16585449 — Estimated prevalence of current adult ADHD 4.4%; ADHD significantly correlated with other DSM-IV disorders.
3. healthdirect (Australian Government). Attention deficit hyperactivity disorder (ADHD). 2025. www.healthdirect.gov.au — ADHD is a neurodevelopmental condition that begins in early childhood; around 1 in 20 people in Australia has ADHD; it is partly genetic; an adult diagnosis requires evidence that symptoms began in childhood; learning difficulties can occur alongside it.
4. Australian ADHD Professionals Association. About ADHD (Australian ADHD Guideline). 2022. adhdguideline.aadpa.com.au — ADHD prevalence is 6–10% in Australian children and 2–6% in adults; heritability 70–80%; symptoms are present before age 12 though diagnosis may come later; 60–86% show symptomatic persistence into adulthood.
5. Better Health Channel (Victorian Government). Attention deficit hyperactivity disorder (ADHD). 2026. www.betterhealth.vic.gov.au — ADHD has a strong genetic component and is not caused by parenting style.
6. Better Health Channel (Victorian Government). ADHD — therapies. 2026. www.betterhealth.vic.gov.au — Stimulants act on dopamine release; short-acting forms last about 3 hours and long-acting forms 6–12+ hours; doses may be increased gradually over 3–4 weeks; there is no evidence ADHD is caused by food additives.
7. Better Health Channel (Victorian Government). ADHD — adults. 2026. www.betterhealth.vic.gov.au — About 7 in 10 children continue to experience ADHD symptoms as adults; treatment can include education, psychological support, coaching, practical strategies and medication.
8. Parliament of Australia — Senate Community Affairs References Committee. Assessment and support services for people with ADHD — Chapter 7: ADHD under the NDIS. 2023. www.aph.gov.au — ADHD does not appear on either NDIS condition list, but people with ADHD can become participants if they meet the disability requirements; 188 participants had ADHD as their primary disability in March 2023.

Sources were last checked on 5 October 2026. See all sources used on this site on our Sources page.