ADHD vs autism: similarities, differences and how they overlap

ADHD and autism are not the same condition and one is not a milder form of the other. ADHD is defined by persistent difficulties with attention, over-activity and impulse control. Autism is defined by differences in social communication and interaction, together with restricted or repetitive behaviours and interests, and differences in sensory experience. In practice the two intersect: many autistic people also have ADHD, and some features, such as trouble with organisation, emotional intensity or difficulty reading social situations, can be present in both.

This is why people are often unsure which label fits. Seeking an assessment that considers both is generally more helpful than trying to pick one from a symptom list. Neither an online checklist nor a single trait can settle the question.

The NHS says symptoms of ADHD usually start before the age of 12 and involve a person's ability to pay attention (inattentive), having high energy levels (hyperactive) and controlling impulses (impulsive). A child may be easily distracted, find it hard to follow instructions, forget everyday tasks, fidget, talk noisily, feel restless or find it hard to wait their turn. Most children and young people have symptoms of both the inattentive and hyperactive-impulsive types, and some show only one. The NHS adds that many children, particularly under 5, are easily distracted and impulsive without having ADHD, as tiredness, anxiety or stress can look similar.

The NHS says the cause is not always known; ADHD may be caused by genetic differences and often runs in families, and it is linked to being born premature, having epilepsy, a brain injury or being autistic. Treatment includes lifestyle measures, support at school and at home, medicines such as methylphenidate that must be started and monitored by an ADHD specialist, and talking therapies such as CBT. Not everyone with ADHD needs or wants medicine.

The NHS says autism, also called autism spectrum disorder, is a difference in how your brain develops that affects how you communicate with people and understand them, how you think, learn and pay attention, and how you respond to light, sounds, smells, tastes and touch. Some autistic people have a learning disability and some have average or above average intelligence. Autistic people are more likely to have conditions such as epilepsy, anxiety, eating disorders or depression, and ADHD is also more common.

In children the NHS describes differences in communicating (speaking later, not responding to their name, using less eye contact), in behaviour and play (repetitive actions, very strong interests, being worried by changes in routine) and in sensory experiences. In adults it lists finding it hard to talk to others, taking things literally, fixed ways of doing things, repetitive movements (stimming), specialist interests and sensory sensitivity. The NHS notes some people learn to adapt so that signs are less noticeable, which is called masking, and that it can be exhausting.

The NHS says autism affects how you think, learn and pay attention, and ADHD affects how you focus, so difficulties with attention, with everyday tasks and with coping at school or work can be raised by either. The NHS says autism may look different in someone who also has ADHD, and it can be difficult to see signs of autism in an adult with another condition such as ADHD. NICE NG87 asks professionals to be aware that people with other neurodevelopmental disorders, including autism, may have an increased prevalence of ADHD.

The underlying reason for a behaviour can differ. A person with ADHD may interrupt because of impulsivity and difficulty waiting; an autistic person may speak at length about a special interest or find the unwritten rules of conversation hard to read. Someone may avoid a busy room because they cannot sustain attention there, or because the sounds and lights are overwhelming. A thorough assessment explores these reasons, not only the behaviour itself.

For ADHD in children, the NHS says assessment is with one or more specialists, such as a paediatrician or child and adolescent psychiatrist, who talk with you and your child, ask about development, usually contact the school, and may use a computer-based test. For autism, the NHS says an assessment team may ask about development and medical history, observe how the child communicates and plays and speak to people who know them well; adults may complete questionnaires and be asked about early life, with someone who knew them as a child. Teams look for other conditions such as ADHD, and can refer on for additional tests.

Waiting times vary and the NHS says that in England you may be able to use Right to Choose to find a service with a shorter wait. If you have both conditions, treatment and support can address each, and NICE says medication choices for ADHD are the same for people who are also autistic, with slower titration and closer monitoring where other neurodevelopmental conditions are present. Speak to a GP if you think you or your child may have either condition.