ADHD (Attention Deficit Hyperactivity Disorder) is a neurodevelopmental condition that affects attention, impulse control, and activity levels. It begins in childhood, although many people are not diagnosed until their teenage years or adulthood.

ADHD is recognised by international diagnostic frameworks and NHS services across the UK. It is not caused by poor parenting, laziness, or a lack of discipline. It reflects differences in how the brain develops and manages executive functions such as focus, organisation, and emotional regulation.

This guide explains:

• What ADHD is

• The three types of ADHD

• Symptoms in children and adults

• How ADHD diagnosis works in the UK

What Is ADHD?

ADHD is a condition that affects how a person regulates attention, activity, and impulses.

Everyone experiences distraction or restlessness at times. ADHD is different because:

• The symptoms are persistent

• They began in childhood

• They affect more than one area of life

• They cause meaningful difficulty in education, work, or relationships

ADHD is considered a neurodevelopmental disorder, meaning it relates to how the brain develops and functions. Research shows strong genetic influences and identifiable differences in brain networks linked to attention and executive functioning.

The Three Types of ADHD

Clinically, ADHD is described in three presentations.

1. Predominantly Inattentive Presentation

Sometimes previously referred to as ADD, though this term is no longer used diagnostically.

Common signs include:

• Difficulty sustaining attention

• Frequently losing items

• Disorganisation

• Forgetfulness

• Avoiding tasks that require sustained mental effort

This type can be overlooked, especially in girls and adults, because it may not involve obvious hyperactivity.

2. Predominantly Hyperactive-Impulsive Presentation

Common signs include:

• Fidgeting or restlessness

• Difficulty staying seated

• Talking excessively

• Interrupting others

• Acting without thinking through consequences

In adults, hyperactivity may present more as inner restlessness rather than visible overactivity.

3. Combined Presentation

This is the most common type and includes a mix of inattentive and hyperactive-impulsive symptoms.

How to Get Diagnosed With ADHD in the UK

The ADHD diagnosis process in the UK is structured and evidence-based.

Step 1: Referral

For NHS services:

• A GP usually makes the referral

• In some cases, schools or mental health teams may refer

• Waiting times vary significantly across regions

For independent services:

• Self-referral may be possible

• Some organisations commission additional assessment capacity

Step 2: Triage and Information Gathering

Before assessment, services may:

• Review referral details

• Request questionnaires

• Prioritise based on clinical need

This helps ensure appropriate and safe allocation of assessment slots.

Step 3: Comprehensive ADHD Assessment

An ADHD assessment is more than a questionnaire.

A high-quality assessment usually includes:

• A detailed clinical interview

• Exploration of childhood history

• Assessment of current functioning

• Consideration of impairment across settings

• Screening for co-existing conditions such as anxiety, depression, autism spectrum traits, sleep difficulties, or substance use

• Risk and safeguarding considerations

This process is designed to ensure diagnostic accuracy and safe next steps.

Step 4: Diagnostic Decision

Diagnosis is made by appropriately qualified clinicians using recognised diagnostic criteria.

Possible outcomes include:

• ADHD diagnosis confirmed

• ADHD not confirmed

• Identification of alternative or additional conditions

Clear documentation should explain the reasoning behind the decision.

Step 5: Treatment and Next Steps

If ADHD is diagnosed, recommendations may include:

• Discussion of medication suitability

• Psychological support

• Workplace or educational adjustments

• Shared-care arrangements where appropriate

A thorough report helps unlock appropriate ongoing care.

ADHD Assessment vs ADHD Screening

An ADHD screening tool is a short questionnaire that indicates whether further assessment might be helpful.

An ADHD assessment is a structured clinical evaluation that determines whether diagnostic criteria are met.

Screening alone cannot provide a diagnosis.

Frequently Asked Questions

Is ADHD overdiagnosed in the UK?

Evidence suggests ADHD has historically been underdiagnosed, particularly in adults and women. Increased awareness has led to more referrals, but diagnostic criteria remain consistent.

Can adults be diagnosed with ADHD?

Yes. ADHD frequently continues into adulthood. Diagnosis requires evidence that symptoms were present in childhood, even if they were not formally recognised at the time.

How long does an ADHD assessment take?

A comprehensive ADHD assessment typically takes several hours and may be delivered across more than one appointment, depending on complexity.

What happens if ADHD is not diagnosed?

A good assessment should still provide clarity, identify alternative explanations, and offer appropriate recommendations for support.