Why they overlap
ADHD and autism turn up together far more often than chance would suggest. You might have an ADHD diagnosis and wonder why loud, busy places drain you so fast, or be autistic and recognise yourself in every list of ADHD traits. Both are linked to how the brain develops, both can run in families, and from the outside they can look surprisingly alike. Having one doesn't mean you have the other, but the overlap is common.
What each one is
The NHS describes ADHD as a condition that affects how you focus, with symptoms around attention, restlessness and controlling impulses. Autism is a difference in how your brain develops that affects how you see and experience the world. According to the NHS guide to autism, it can affect how you communicate and understand people, how you pay attention, and how you react to light, sound, smells, tastes and touch. The NHS also says ADHD is more common in autistic people.
How often together
A 2019 review of 96 studies estimated that about 28% of autistic people also have an ADHD diagnosis, much higher than usual general population rates. Figures were higher in studies of people attending clinics than in whole-population studies. Some papers quote 50 to 70%, but researchers still debate how much of the attention difficulty seen in autism is truly ADHD and how much is part of autism itself, so treat any single figure with caution.
Shared family links
A Swedish study of almost 1.9 million people born between 1987 and 2006 found that autistic people were far more likely to also have ADHD. Their relatives were more likely to have ADHD too, and the link was strongest in identical twins, who share almost all their genes. That pattern suggests the two conditions share some genetic roots. It doesn't mean one causes the other, and it can't tell you anything about your own family on its own.
Where they look alike
Plenty of everyday moments can look the same from outside. You zone out in a meeting, but is it because your attention wandered off, or because the strip lights and chatter have become too much? Six hours on one thing without eating could be ADHD hyperfocus or a deep autistic interest. The NHS notes that signs of autism can be harder to spot in adults who also have ADHD, which is one reason the overlap gets missed.
Where they differ
The clearest differences tend to show up in social communication and routine. NHS signs of autism in adults include finding facial expressions or tone of voice hard to read, taking things literally, having fixed ways of doing things and getting distressed when a routine changes. ADHD signs are more about distraction, forgetfulness, restlessness and acting on impulse. With both, the two can pull against each other, like wanting a fixed routine but finding it hard to organise your time.
Getting assessed
The NHS says a GP looking at ADHD may also consider conditions such as autism, Tourette's or anxiety, and autism assessment teams look for signs of ADHD too. A GP can refer you to a local autism team, and waits can be months or longer. Before your appointment, jot down a week of real examples, like the noisy office that wiped you out or the plan change that threw your day, and ask someone who knew you as a child.
Treatment and support
Autism has no treatment or cure, but support is available. For ADHD, the NICE guideline on ADHD says autistic people with ADHD should be offered the same medication choices as anyone else with ADHD. It also says doses should be adjusted more slowly and checked more often when someone has a condition like autism. If you think you might have both, talk to a GP or prescriber, and don't change any current treatment without speaking to them first.
This information is for general education and is not personalised medical advice. Treatment and prescribing decisions belong to qualified healthcare professionals.