What is the difference between ADHD and autism? A clinical breakdown

Understanding the distinction between autism spectrum disorder (ASD) and attention deficit hyperactivity disorder (ADHD) is crucial, for both clinicians and healthcare professionals. These disparate neurodivergences share overlapping traits1, leading to frequent misdiagnosis or delayed identification2,3. However, despite their similarities, ADHD and autism manifest in distinct ways that affect cognition, behaviour, and social interactions very differently.

Both conditions are increasingly recognised as part of the broader neurodiversity paradigm, emphasising differences rather than deficits. Research indicates that ADHD affects approximately 5% of children and 3-4% of adults in the UK4, while autism is estimated to affect around 1.1% of the population5. Accurate diagnosis and appropriate support strategies depend on a nuanced understanding of each condition’s core characteristics, underlying neurological mechanisms, and real-world impact.

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What is ADHD? 

ADHD is a neurodevelopmental condition characterised by persistent patterns of inattention, hyperactivity, and impulsivity that interfere with daily functioning6. The condition arises from dysregulation in the brain’s dopaminergic and noradrenergic systems7, particularly in the prefrontal cortex, which governs executive function, impulse control, and attention regulation.

For example, a business leader with ADHD might struggle with task prioritisation, time management, and impulse regulation but thrive in high-pressure, fast-paced environments8 that align with their unique strengths. 

Research suggests that genetic predisposition, prenatal factors, and early childhood development all contribute to the presentation of ADHD9. Despite common misconceptions, ADHD is not solely a ‘childhood disorder’10 – many individuals continue to experience symptoms into adulthood, affecting work performance, relationships, and mental health.

Defining characteristics

ADHD presents with three primary subtypes:

• Predominantly inattentive type: difficulty sustaining attention, forgetfulness, apparent disorganisation, and difficulty following through on tasks.
• Predominantly hyperactive-impulsive type: excessive talking, fidgeting, restlessness, impulsive decision-making, and difficulty waiting for turns.
• Combined type: a mix of both inattentive and hyperactive-impulsive traits.

The degree of symptom severity varies between individuals, with some demonstrating high cognitive adaptability and compensatory strategies, while others may experience significant functional impairments.

What is autism?

Meanwhile, autism is a complex presentation characterised by differences in social communication, sensory processing, and cognitive flexibility. Unlike ADHD, which primarily affects attention and impulse control, autism involves altered neural connectivity patterns14 that shape perception, behaviour, and emotional regulation.

For instance: consider a media personality with autism. While they may have a deep focus on their area of expertise and excel in structured environments, they may also find spontaneous social interactions challenging. 

It’s important to say that autism is not a disease or disorder to be ‘cured’, but rather a neurotype with distinct strengths and challenges – arguably better thought of simply as differences15,16. It is diagnosed based on behavioural criteria outlined in the DSM-5, and is understood as a spectrum due to the wide variability in traits and functional capacities.

Defining characteristics 

Autistic traits do vary widely but can often include:

• Social communication differences: challenges interpreting social cues, maintaining eye contact, and understanding implicit meanings in conversations.
• Repetitive behaviours and routines: strong preference for predictability, repetitive motor movements (eg., hand-flapping, rocking), or deep, specialised interests.
• Sensory processing differences: heightened or diminished responses to sensory stimuli such as sounds, textures, or lights.
• Cognitive and emotional regulation differences: unique problem-solving approaches, challenges adapting to sudden changes, and atypical emotional responses.

Why autism and ADHD are sometimes confused

Both ADHD and autism share traits such as executive functioning difficulties, sensory sensitivities, and social interaction challenges20, leading to frequent misidentification21. However, the core differences lie in their underlying neurological mechanisms:

→ ADHD is primarily linked to deficits in attentional control and impulse regulation, whereas autism involves differences in social cognition and sensory processing.

Moreover, traditional diagnostic models often fail to account for the diversity of presentations, particularly in females22. Misdiagnosis can lead to ineffective treatment strategies – highlighting the need for specialised assessment protocols that more clearly differentiate the two conditions.

How to distinguish between ADHD and autism

Accurate differentiation between ADHD and autism requires a multi-pronged diagnostic approach. Key factors include:

• Social motivation: individuals with ADHD may struggle with social reciprocity due to impulsivity, whereas autistic individuals may find social interaction inherently challenging.
• Executive function: ADHD primarily affects working memory and cognitive flexibility, while autism is associated with more rigid thinking patterns and intense focus on specific interests.
• Sensory processing: while both involve sensory differences, autistic individuals tend to have more pronounced and consistent sensory sensitivities.
• Developmental history: a thorough analysis of early developmental milestones can provide revelatory diagnostic clues.

Can ADHD and autism co-occur? 

Yes, ADHD and autism frequently co-occur. 

Studies indicate that up to 50% of autistic individuals also manifest ADHD symptoms23. The high rate of comorbidity may suggest shared genetic and neurological underpinnings24.

How common is it? 

According to one study, the co-occurrence rate of ADHD in autistic individuals is significantly higher25 than in the general population. The prevalence of dual diagnoses emphasises the clinical need for an integrated approach to assessment and management, ensuring that individuals receive appropriate support.

Helping manage neurodivergence in the heart of the city

Both ADHD and autism represent natural variations in human cognition – not disorders that need to be ‘fixed.’ By embracing a neurodiversity-affirming approach, clinicians can support individuals in leveraging their strengths while mitigating any specific challenges.

Harbor London provides specialised multidisciplinary services and curated intervention strategies that acknowledge the uniqueness of every neurodivergent individual. Our whole-person approach ensures that patients receive tailored care, integrating clinical expertise with compassionate understanding. 

By fostering inclusive healthcare, we aim to empower individuals to thrive in work, relationships, and daily life – transforming so-called ‘challenges’ into opportunities for growth.

For expert assessment and support, contact Harbor London today.

References 

1. https://www.autistica.org.uk/what-is-autism/adhd-and-autism
2. https://neurodivergentinsights.com/misdiagnosis-monday/adhd-vs-autism
3. https://pmc.ncbi.nlm.nih.gov/articles/PMC6512047/
4. https://www.england.nhs.uk/long-read/attention-deficit-hyperactivity-disorder-adhd-programme-update/#:~:text=The%20National%20Institute%20for%20Health,terms%20of%20completeness%20and%20coverage.
5. https://cks.nice.org.uk/topics/autism-in-adults/background-information/prevalence/#:~:text=Prevalence-,How%20common%20is%20it%3F,2023%3B%20NCCMH%2C%202023%5D.
6. https://www.psychiatry.org/patients-families/adhd/what-is-adhd
7. https://www.sciencedirect.com/science/article/pii/S0006322311002605#:~:text=Dysregulated%20dopaminergic%20and%20noradrenergic%20neurotransmission,yields%20the%20latter%20(6).
8. https://www.theguardian.com/society/2018/mar/18/people-with-adhd-incredibly-valuable-at-work-diagnosis-support
9. https://cks.nice.org.uk/topics/attention-deficit-hyperactivity-disorder/background-information/causes/
10. https://chadd.org/about-adhd/myths-and-misunderstandings/
11. https://pmc.ncbi.nlm.nih.gov/articles/PMC4437560/
12. https://www.healthline.com/health/adhd/adhd-dopamine#:~:text=Some%20research%20in%20animals%20and,stimulants%20and%20include%20amphetamines%20like:
13. https://www.psychiatrist.com/jcp/emerging-therapies-adhd/
14. https://pmc.ncbi.nlm.nih.gov/articles/PMC4843767/
15. https://www.autistica.org.uk/what-is-autism/autistic-strengths
16. https://www.autistica.org.uk/what-is-autism/challenges-autistic-people-face
17. https://www.frontiersin.org/journals/neuroscience/articles/10.3389/fnins.2023.1125428/full#:~:text=In%20autism%20models%2C%20a%20transient,et%20al.%2C%202014).
18. https://www.pnas.org/doi/10.1073/pnas.1214533110#:~:text=The%20nature%20of%20functional%20connectivity,entire%20cortical%20lobes%20(12).
19. https://pmc.ncbi.nlm.nih.gov/articles/PMC4105225/
20. https://www.autismparentingmagazine.com/learn-autism-differences/
21. https://www.healthline.com/health/adhd/autism-and-adhd
22. https://www.additudemag.com/autism-in-women-adhd-signs-symptoms-treatment/?srsltid=AfmBOooTdzAhzaX-81t1oPEn8r1SORNFQOFoeJdsjY0DvA9bls4chM_o
23. https://pmc.ncbi.nlm.nih.gov/articles/PMC4010758/#:~:text=While%20ADHD%20is%20defined%20by,pre%2Dschool%20age)%2C%20and
24. https://pubmed.ncbi.nlm.nih.gov/20148275/#:~:text=Attention%2Ddeficit/hyperactivity%20disorder%20(,to%20tackle%20this%20complex%20issue.

https://pmc.ncbi.nlm.nih.gov/articles/PMC8918663/#:~:text=According%20to%20the%20scientific%20literature,rate%20of%20comorbidity%20is%20intriguing.