ADHD and autism

The short answer

ADHD and autism are both neurodevelopmental conditions, which means they relate to how the brain develops and are present from childhood. ADHD mainly affects attention, activity levels and impulse control. Autism mainly affects social communication and interaction, and often involves a strong preference for routine, focused interests and differences in how the senses process information.

The two share some features and often occur in the same person. This is why a careful assessment matters: it looks at which condition explains your difficulties, or whether both do. ADH-Me assesses ADHD in adults and children. If autism is suspected during an assessment, our specialist will discuss the next steps with you. The free adult screening or the free child screening is a useful first step, although a screening questionnaire is not a diagnosis.

How ADHD and autism differ

The core features of each condition are different, even where some behaviours look alike.

• ADHD is defined by inattention, hyperactivity and impulsivity. In practice this can mean losing focus, difficulty organising and starting tasks, forgetfulness, restlessness and acting or speaking before thinking. Our guides to adult ADHD symptoms and ADHD in children describe these in more detail.
• Autism is defined by differences in social communication and interaction, such as reading unspoken social rules, tone and body language, together with restricted or repetitive behaviours and interests, a need for sameness, and sensitivity to sound, light, touch or other sensations.

The reason behind a behaviour is often what separates the two. A child who does not follow an instruction in class may have drifted off and missed it, which is more typical of ADHD, or may have found it unclear or the room overwhelming, which is more typical of autism. Many autistic people find comfort in routine and predictability, while many people with ADHD find routines hard to keep and are drawn to novelty. People with both conditions often describe feeling both pulls at once.

Where they overlap

Some experiences are common to both conditions, which is one reason they can be difficult to tell apart:

• Difficulty with attention, although for different reasons
• Difficulty planning, organising and switching between tasks
• Strong emotions that are hard to regulate, and feeling easily overwhelmed
• Sensitivity to noise, busy places or certain textures
• Periods of intense focus on a subject of interest
• Difficulties with friendships and social situations

Both conditions can also be hidden by masking, where a person copies others and works hard to appear as expected. Masking is often described by females, and it is one reason both conditions can be missed until adulthood. Our guide to ADHD in females explains this further.

Why they often occur together

ADHD and autism frequently occur in the same person and often run in the same families. Both begin early in development, and research suggests they share some genetic influences. NICE guideline NG87, the national guidance on ADHD, asks professionals to be aware that ADHD is more common in people with other neurodevelopmental conditions, including autism.

For many years, the main diagnostic manuals did not allow ADHD to be diagnosed in someone who had already been diagnosed with autism. Current versions allow both, which is one reason more people now receive a second diagnosis later in life. Some people use the informal term AuDHD to describe having both.

How having both affects an assessment

When two conditions overlap, one can hide the other. Someone diagnosed with autism in childhood may have had their difficulties with attention put down to autism. Someone diagnosed with ADHD may have had social or sensory differences put down to ADHD. Anxiety can complicate the picture further, and we explain that in our guide to ADHD and anxiety.

NICE publishes separate guidance on diagnosing ADHD and on recognising and diagnosing autism. Both describe a thorough assessment of a person's development, history and daily life rather than a questionnaire alone, and both ask clinicians to consider other conditions that may be present. In an ADHD assessment, this means the clinician will usually:

• Ask about early development, school and how you or your child got on with other children
• Look for ADHD symptoms in childhood. ADHD symptoms begin in childhood, and the diagnostic criteria require several symptoms to be present before the age of 12
• Consider whether difficulties with attention or behaviour are better explained by autism, anxiety or something else
• Use rating scales and, at ADH-Me, the QbCheck test, which measures attention, activity and impulsivity. It is not a test for autism

Our guide to what happens in an ADHD assessment sets out each stage.

What this means for getting assessed

• If you already have an autism diagnosis and recognise ADHD traits as well, an ADHD assessment can establish whether ADHD is also present. Please share any previous reports, as they help the clinician understand your history.
• If you suspect both, you can still begin with an ADHD assessment. ADH-Me assesses ADHD. If autism is suspected during your assessment, one of our specialists will discuss the next steps with you. Your GP can advise on the local NHS route for an autism assessment.
• If you are a parent in Wales, it is worth knowing that some Welsh health boards assess autism and ADHD together for children through a combined neurodevelopmental pathway. Our page on ADHD waiting times in Wales shows NHS waits by health board and explains which boards report combined assessments.

Whichever applies, it helps to note down what you notice now and what you remember from childhood, and to find old school reports if you have them. If you would like to discuss your situation before deciding, get in touch and we will advise on whether an ADHD assessment is the right next step.