What Is ADHD? A Clear Definition for UK Adults

The National Health Service (NHS) defines Attention-Deficit/Hyperactivity Disorder (ADHD) as a condition where the brain functions differently from that of most other people.^[1]

Many studies have proven that ADHD is a genuine medical condition with a real effect on daily life. While it is commonly associated with children, it can also impact adults, affecting their work or relationships. 

Having a clear understanding of what ADHD is can make a real difference. For many adults, recognising it brings greater clarity and opens the door to professional help and support.

Understanding ADHD: What Does It Mean?

ADHD is officially defined as a condition that changes how the brain works. It’s not just about being occasionally distracted or restless. Instead, it is a long-term condition that alters information processing in the brain. 

Let’s break down what this really means for adults.

ADHD as a Neurodevelopmental Condition

ADHD is not due to laziness or poor parenting. 

ADHD is what doctors call a neurodevelopmental condition. In other words, it affects the way the brain develops and functions from a young age. This causes differences in your thoughts, behaviours, and habits when compared to people without ADHD.

Research shows that ADHD can alter the function of the brain in various ways. Studies suggest there may be differences in the size and structure of certain brain regions. ADHD is also linked to changes in the levels of chemical messengers that regulate our behaviour.^[2][3]

Essentially, the ADHD brain is wired in a unique way. 

How the Term Has Evolved Over Time

The language around ADHD has shifted over the years. 

In the past, terms like “ADD” (Attention Deficit Disorder) were used. Individuals were diagnosed with “ADD with hyperactivity” or “ADD without hyperactivity.”

Today, the medical community uses the broader term ADHD. This term recognises hyperactivity as an important feature of the condition, but not everyone with ADHD will have it. It also reflects the different ways ADHD can show up in people’s lives.

The Role of UK Guidelines

In the UK, the diagnosis and treatment of ADHD are shaped by guidelines from two main organisations. They are the National Health Service (NHS) and the National Institute for Health and Care Excellence (NICE).^[4]

These guidelines ensure that healthcare professionals diagnose and manage ADHD with evidence-backed approaches. Over time, they have also been updated to ensure adults receive the same level of recognition and care for ADHD as children do.

Symptoms that Define ADHD

ADHD symptoms can impact work, relationships, and daily tasks, but recognizing them is the first step toward getting help.

The hallmark symptoms of ADHD are split into several main categories below. 

Inattention

Symptoms of inattention in adult ADHD typically include the following:^[5]

• Difficulty staying focused on tasks that aren’t interesting
• Making careless mistakes from overlooking details
• Struggling to complete tasks as instructed
• Trouble organising and prioritising responsibilities
• Lacking time management skills
• Avoiding or procrastinating on tasks that require sustained effort
• Frequently misplacing important items or documents
• Being forgetful in daily life, such as missing appointments or bill payments

Hyperactivity and Restlessness

Hyperactivity in adults doesn’t always mirror that in children. It’s usually more subtle and can show up in the following ways:^[5]

• Fidgeting and squirming about in your seat
• Being unable to sit still
• Experiencing inner restlessness
• Feeling the need to stay busy
• Always out-and-about and on-the-go
• Talking excessively

Impulsivity

Impulsivity in ADHD can lead to the symptoms below:^[5]

• Interrupting other people and finishing their sentences
• Having trouble being patient and waiting for your turn
• Intruding or taking over what other people are doing
• Impulsive spending
• Reckless driving
• Substance use

Impulsivity can lead to acting or speaking without considering the consequences. This may affect your decision-making and relationships.

Emotional Regulation Difficulties

Many adults with ADHD find it harder to manage difficult emotions. You might notice yourself blaming yourself or others, expecting the worst, or getting stuck on negative thoughts – and that’s completely understandable given how ADHD affects the brain.^[6]

Strong emotions like frustration, anger, or disappointment can feel overwhelming. Remember, this isn’t a character flaw; it’s part of how ADHD affects emotional processing.

Executive Function Challenges

Executive functions are brain skills that help you focus, plan ahead, remember details, and control your impulses.

When you have ADHD, these skills often don’t work as well. This might mean missing deadlines, being late, struggling with motivation, or having difficulty sticking to routines. The good news? Understanding this is the first step, and there are strategies that can help.

What Causes ADHD in the Brain?

Currently, the exact cause of ADHD is still unclear. However, researchers suggest that ADHD can be linked to a combination of genetic and environmental factors.

Brain Structure and Function

ADHD is linked to differences in the structure and function of the ADHD brain. 

Affected regions may include the following:^[7]

• Insula: Supports attention, emotional regulation, and self-control
• Superior temporal gyrus: Involved in language and spatial awareness
• Cerebellum: Supports motor skills, learning, and attention shifting

This might explain why ADHDers experience challenges with focus, planning, or regulating emotions. 

Neurotransmitter Involvement

Neurotransmitters are chemical messengers. They allow nerve cells to communicate with each other or with other cells all over your body. 

ADHD is linked to changes in the levels of neurotransmitters in the brain. The main ones affected are dopamine and noradrenaline.^[3]

These chemical messengers play a crucial role in regulating attention, memory, motivation, and reward processing. When levels are disrupted, it can be harder to focus, stay motivated, and remember details.

Genetic and Hereditary Factors

ADHD often runs in families as it demonstrates a strong genetic link. In fact, some research suggests that it has a heritability of 80%.^[8]

So if your parent or close relative has ADHD, there is a higher likelihood that you might develop it too.

Environmental Influences

Environmental factors can also play a role in increasing the risk of ADHD.

Some of them include:^[9]

• Maternal exposure to alcohol, tobacco, or drugs during pregnancy
• Exposure to secondhand smoke
• Low birth weight or premature birth
• Early exposure to toxins such as lead

These are unlikely to cause ADHD on their own but may contribute to its development.

Is ADHD Considered a Medical Condition?

ADHD is recognised as a legitimate medical condition by health organisations. 

It’s important to note that ADHD is not simply a personality trait, laziness, or a lack of willpower. Instead, it is a well-defined condition that can be diagnosed and treated.

Recognition in Medical Classifications

ADHD is listed in various diagnostic manuals. These include:

• The Diagnostic and Statistical Manual of Mental Disorders (DSM-5)
• The International Classification of Diseases (ICD-10 and ICD-11).

These manuals give healthcare professionals guidelines on how to diagnose and treat ADHD. 

NHS and NICE Position

In the UK, ADHD is commonly diagnosed and managed following the NICE guidelines. These guidelines help ensure consistency and accuracy in the diagnosis and care of people with ADHD. 

Meanwhile, the NHS provides an affordable option for individuals to seek assessment and treatment for ADHD. Under the Right to Choose scheme, individuals can select their preferred ADHD specialist for an assessment. 

This further highlights ADHD as a real medical condition that deserves proper, subsidised care.

ADHD as a Lifelong Condition

While symptoms of ADHD typically start in childhood, they can often persist into adulthood. 

Numerous research studies have disputed the common idea that ADHD is only a childhood condition. In fact, many adults also experience its impact in their daily lives. 

Symptoms can also change over time. This means a person’s needs and required level of support might shift over their lifetime.

Is ADHD a Disability in the UK?

ADHD may be classified as a disability, but this depends on how much it affects your daily life.

Let’s explore how ADHD can be legally considered a disability.

Equality Act 2010 Criteria

Under the Equality Act 2010, a person is considered to have a disability when both conditions below are met:^[10]

• They have a mental or physical impairment.
• This impairment has a long-term and significant impact on the person’s ability to perform their daily activities.

So if ADHD leads to symptoms that make it difficult for you to carry out your everyday responsibilities, it can be considered a disability. With this act in place, individuals can gain access to reasonable support and accommodations to help them succeed.

Workplace Adjustments and Support

Employees with a formal diagnosis of ADHD are legally able to request reasonable adjustments at work. 

Some examples of these include:

• Flexible working hours
• Written instructions
• A quiet workspace
• Noise-cancelling headphones
• A standing desk
• Shorter but more frequent breaks

These adjustments can create a supportive work environment. That way, they can reach their full potential and secure similar opportunities as their peers.

Are You Born With ADHD?

Research suggests that ADHD is linked to genetic factors and tends to run in families. So, some individuals might be born with genes that put them at a higher risk of developing ADHD.^[9] In other words, it appears possible to be “born with ADHD.”

This is also why an official diagnosis requires symptoms to have appeared before the age of 12. Examples of these early signs include being restless, having trouble focusing, and talking a lot. 

That said, many people are only diagnosed as adults, and that’s perfectly valid. Your symptoms in childhood might have been missed. Getting diagnosed later in life doesn’t make your ADHD any less real.

ADHD in Adults Should Not be Overlooked

ADHD is a real medical condition that can change how adults tackle their daily activities. 

If you’re considering an assessment for ADHD as an adult, remember that it’s never too late. With the right support, treatment, and strategies, you can put yourself in the best position to reach your daily goals.

Want to learn more about adult ADHD and how to manage its symptoms? Check out ADDA+. This resource hub provides support groups, courses, and practical guidance to help adults with ADHD achieve their goals and thrive.

References

[1] NHS. (2025). ADHD in adults. Nhs.uk. https://www.nhs.uk/conditions/adhd-adults/

‌[2] Yu, M., Gao, X., Niu, X., Zhang, M., Yang, Z., Han, S., Cheng, J., & Zhang, Y. (2023). Meta-analysis of structural and functional alterations of brain in patients with attention-deficit/hyperactivity disorder. Frontiers in psychiatry, 13, 1070142. https://doi.org/10.3389/fpsyt.2022.1070142

[3] da Silva, B. S., Grevet, E. H., Silva, L. C. F., Ramos, J. K. N., Rovaris, D. L., & Bau, C. H. D. (2023). An overview on neurobiology and therapeutics of attention-deficit/hyperactivity disorder. Discover mental health, 3(1), 2. https://doi.org/10.1007/s44192-022-00030-1

[4] NICE. (2018). Attention Deficit Hyperactivity disorder: Diagnosis and Management | Guidance | NICE. Nice.org.uk; NICE. https://www.nice.org.uk/guidance/ng87

[5] de la Peña, I. C., Pan, M. C., Thai, C. G., & Alisso, T. (2020). Attention-Deficit/Hyperactivity Disorder Predominantly Inattentive Subtype/Presentation: Research Progress and Translational Studies. Brain sciences, 10(5), 292. https://doi.org/10.3390/brainsci10050292

[6] Soler-Gutiérrez, A. M., Pérez-González, J. C., & Mayas, J. (2023). Evidence of emotion dysregulation as a core symptom of adult ADHD: A systematic review. PloS one, 18(1), e0280131. https://doi.org/10.1371/journal.pone.0280131

[7] Agoalikum, E., Klugah-Brown, B., Wu, H., Hu, P., Jing, J., & Biswal, B. (2023). Structural differences among children, adolescents, and adults with attention-deficit/hyperactivity disorder and abnormal Granger causality of the right pallidum and whole-brain. Frontiers in human neuroscience, 17, 1076873. https://doi.org/10.3389/fnhum.2023.1076873

[8] Balogh, L., Pulay, A. J., & Réthelyi, J. M. (2022). Genetics in the ADHD Clinic: How Can Genetic Testing Support the Current Clinical Practice?. Frontiers in psychology, 13, 751041. https://doi.org/10.3389/fpsyg.2022.751041

[9] Hussein, R. A., Refai, R. H., El-Zoka, A. H., Azouz, H. G., & Hussein, M. F. (2025). Association between some environmental risk factors and attention-deficit hyperactivity disorder among children in Egypt: a case-control study. Italian journal of pediatrics, 51(1), 19. https://doi.org/10.1186/s13052-025-01843-w

[10] UK Government. (2010). Equality Act 2010. Legislation.gov.uk. https://www.legislation.gov.uk/ukpga/2010/15/section/6