The 3 Main Features of ADHD Explained: What Defines ADHD Today

Ever feel like your brain runs on a completely different operating system? For millions of Brits, that feeling has a name: Attention Deficit Hyperactivity Disorder. It’s a genuine condition where the brain functions differently. It's not a flaw.

ADHD Overview: Understanding the Condition

Let's start with a clear picture of what ADHD is. The National Health Service (NHS) describes it as a condition where the brain works differently from that of most people, which can result in trouble with things like concentrating and sitting still. It is not a new fad or an excuse for poor behaviour. The World Health Organization defines it as a “persistent pattern of inattention or hyperactivity-impulsivity that has a direct negative impact on academic, occupational, or social functioning”.

For decades, ADHD was seen as a childhood issue, but we now know it affects people across their entire lives.

The conversation around ADHD has become much louder in recent years. What looks like a new "boom" is actually a long-overdue recognition. In England alone, it's estimated that nearly 2.5 million people have ADHD.

Here’s the reality of that recognition: only about 1 in 9 people in the UK with ADHD have a formal diagnosis.

Those 2 million-plus undiagnosed individuals are now seeking help, and the system is struggling to cope. The situation has become so critical that in 2025, NHS England launched its first-ever ADHD Taskforce to tackle the crisis.

What about "ADD"? Understanding the Types of ADHD

You might be thinking, "I'm not hyperactive, so I can't have ADHD." It's a very common misconception.

You may remember the term "ADD" or Attention Deficit Disorder. That term is now obsolete. Clinicians today use the single term "ADHD" and classify it into three different "presentations" or types of adhd. What was once called ADD is now "Predominantly Inattentive Presentation."

A diagnosis depends on which symptoms of adhd a person has, how many they have, and how long they've been present (at least 6 months, in two or more settings like home and work). For adults aged 17 and older, five symptoms are required; for children, six are needed.

The three presentations are:

1. Predominantly Inattentive Presentation (20%-30% of cases): A person has enough inattentive symptoms but very few hyperactive-impulsive ones. It's the "classic" ADD profile.
2. Predominantly Hyperactive-Impulsive Presentation (15% of cases): A person has enough hyperactive-impulsive symptoms but struggles less with inattention.
3. Combined Presentation (50%-75% of cases): A person has enough symptoms of both inattention and hyperactivity-impulsivity. It's the most common presentation.

Core Feature 1: Inattention

Inattention is the feature that targets a person’s focus and organisation. It's the symptom cluster most people associate with old-fashioned "ADD."

The official diagnostic criteria list many symptoms of adhd related to inattention. A person may often:

• Fail to give close attention to details or make "careless" mistakes at work or in school.
• Have difficulty sustaining attention in tasks, such as during long readings or lectures.
• Not seem to listen when spoken to directly (their mind seems elsewhere).
• Not follow through on instructions and fail to finish tasks.
• Lose things necessary for tasks, like keys, wallets, phones, or paperwork.
• Become easily distracted.
• Be forgetful in daily activities, like paying bills or keeping appointments.

What does that feel like?

It’s sitting in an important work meeting, trying to focus, but "zoning out." At the end, you feel a wave of shame as you realise you've missed half of what was said.

It’s starting to write an important email, hearing a notification, and 20 minutes later, you're deep in a research hole about an unrelated topic, and the email is completely forgotten.

It’s the pile of unopened mail on the kitchen counter because the task of filling out forms or paying bills feels mentally painful.

It’s the constant, exhausting mental effort required to try and stay focused. The messy desk or cluttered home isn't a sign of laziness; it's often a sign of a brain that is overwhelmed and fatigued.

The Deeper Issue: Executive Dysfunction

These symptoms are all part of a deeper challenge: executive dysfunction.

Executive functions are your brain's "internal management system". They are the high-level skills that help you plan, prioritise, manage your time, and regulate your emotions.

ADHD is, at its root, a "condition that disrupts executive functioning".

Struggling with organisation, chronic lateness, and procrastination are not separate moral failings. They are symptoms of a breakdown in the brain's "admin" system.

Core Feature 2: Hyperactivity

Hyperactivity is the most stereotyped feature of ADHD. It's the "H" in the name.

The classic clinical symptoms include:

• Fidgeting with or tapping hands or feet, or squirming in a seat.
• Leaving a seat in situations when remaining seated is expected (like an office).
• Being unable to play or do leisure activities quietly.
• Feeling "always 'on the go,' as if driven by a motor."
• Talking excessively.

For many adults, especially women, "hyperactivity" looks very different. The symptom manifestation changes over time.

This is the most important takeaway: in adults, the "H" often goes underground.

A child’s hyperactivity is external and obvious: running, jumping, and climbing constantly. As that person grows up, they learn (or are forced) to suppress those obvious behaviours.

But the feeling doesn't go away. It just internalises.

Adult hyperactivity often feels like:

• A powerful, persistent "inner restlessness".
• Feeling "edgy" or constantly "on the go".
• "Racing thoughts" or a mind that just won't turn off.
• Subtle fidgeting, like jiggling a foot, tapping a pen, or shifting in a chair.
• A profound inability to just sit and relax; feeling uncomfortable just being still.
• Needing to be busy, often trying to do multiple things at once.

It’s that "driven by a motor" feeling, but the motor is inside your brain and your chest.

A key reason ADHD is "recognised less often in women than men" is that girls are more likely to have this less-disruptive, internalised hyperactivity. They don't fit the "disruptive boy" stereotype, so their struggles are often missed.

Core Feature 3: Impulsivity

Impulsivity is often grouped with hyperactivity. It’s defined as "acting without thinking" or having "trouble with self-control". It's a problem with the brain's braking system.

The clinical criteria include:

• Blurting out an answer before a question has been finished.
• Having difficulty waiting for a turn (like in a queue).
• Interrupting or intruding on others.

Like hyperactivity, "impulsivity" in adults is about more than just physical risk. It has profound social, verbal, and financial consequences.

• Verbal Impulsivity: It’s the "no filter" feeling. It’s finishing people's sentences or blurting out a thought. It’s interrupting a conversation, not to be rude, but because your brain can't hold the thought and wait for its turn.
• Emotional Impulsivity: It can appear as a "quick temper" or a "low tolerance for frustration". It’s a sudden flash of anger or a wave of emotion that feels out of proportion.
• Financial and Life Impulsivity: It’s the "impulsive purchases". It’s also the bigger, hasty decisions about jobs, relationships, or engaging in risky behaviours without fully thinking through the consequences.

How ADHD Symptoms Vary in Adults vs Children

So, to pull it all together: the core symptoms of ADHD are the same, but the way they look can be very different.

In children, symptoms are often "more noticeable". They are external and physical.

In adults, the symptoms "tend to appear in subtler ways".

• Hyperactivity often becomes that "inner restlessness".
• Inattention persists and evolves into more complex executive dysfunction (poor time management, disorganisation).
• Adults often struggle more with emotional regulation.

There's one final piece of the puzzle: masking.

As adults, people with undiagnosed ADHD have spent a lifetime trying to "fit in." They learn to hide their symptoms. They might over-compensate with endless checklists or appear anxious. They might withdraw socially to avoid interrupting people.

Masking is an exhausting, 24/7 performance. It’s a major reason ADHD is harder to recognise in adults and why a diagnosis can feel like a revelation.

Symptom Manifestation: Children vs. Adults

The Tangled Link Between ADHD and Anxiety

It is very common for people with ADHD to also struggle with other conditions. A 2025 study highlighted the "high comorbidity rate" between ADHD and other psychiatric conditions, especially adhd and anxiety and depression.

So what’s the connection? It's a bit of a "chicken-and-egg" situation.

• Life-Experience Anxiety: Living with undiagnosed ADHD is incredibly stressful. The constant frustration of missing deadlines, forgetting appointments, and feeling disorganised can lead to "feelings of inadequacy and low self-esteem," which in turn contribute to developing anxiety. Doctors call one form "secondary anxiety"—it’s anxiety about the ADHD difficulties.
• Neurological Anxiety: The conditions may also share biological roots. 2025 research suggests ADHD isn't just a "frontal lobe" issue; it’s also linked to "emotional dysregulation" and an "increased excitability in the limbic system"—the brain's emotion and threat centre. A person’s brain wiring may leave them vulnerable to both.

Is There an ADHD Attention Deficit Disorder Test?

Many people ask, "How do I get an adhd attention deficit disorder test?"

Here’s the simple truth: There is no single test to diagnose ADHD.

You can't get a blood test, brain scan, or simple quiz that gives you a definitive answer. Symptoms can overlap with other conditions, like sleep disorders, anxiety, or depression.

A diagnosis is not a test; it's a biography.

According to official NICE guidelines, a diagnosis can only be made by a specialist (like a psychiatrist or paediatrician) after a "full clinical and psychosocial assessment".

What does that mean? It's an in-depth conversation. The specialist will ask about your entire life: your childhood, your school days, your work, and your relationships. They are looking for that "persistent pattern" and will gather a "full developmental and psychiatric history".

The NHS pathway in the UK starts with your GP. You visit them, explain your symptoms and how they affect your life, and they can refer you to a specialist. Given the long waits, it's worth knowing that in England, you have a "Right to Choose." It allows you to ask your GP for a referral to a private provider that has an NHS contract, which can sometimes be faster.

Summary

Understanding ADHD isn't about finding a label for flaws. It's about getting a clearer picture of how a person's brain is wired. These three features—inattention, hyperactivity, and impulsivity—are not character failings. They are the defining traits of a different way of processing the world. That clarity can be the first step toward finding the right support.