Why 45% of adults with ADHD may also be autistic

Published 5 April 2026 · 8 min read

Here's a number that should have been front-page news and wasn't: a 2025 study estimated that roughly 45 percent of adults with ADHD show significant autistic traits. Not 5 percent. Not 15 percent. Forty-five. If you're an adult with ADHD reading this, there's almost a coin-flip chance you're also somewhere on the autism spectrum — and probably weren't told.

How can the number be that high?

Three reasons. First, the diagnostic separation between ADHD and autism was artificial for decades — if you met criteria for one, the other was off-limits in many clinics. Second, autism in adults (especially women and anyone who masks) has been chronically under-diagnosed. Third, the shared brain features between ADHD and autism — sensory differences, executive function challenges, emotional regulation patterns — mean the populations were always going to overlap more than the old rulebooks allowed.

Why it matters

Because the treatment plan changes. An adult with "just ADHD" is often handed stimulants and a productivity planner. An adult with AuDHD needs the medication conversation and the sensory conversation and the masking conversation and the burnout conversation. Skipping three of those four is why so many adults describe their ADHD treatment as "sort of helped but not really".

"If the plan only works half the time, the plan is only treating half of you."

How to know if you're in the 45 percent

There isn't a DIY test. But there are signals that make it worth asking. You've been told you're good at your job but terrible at the social side of it. You find small talk genuinely exhausting, not just boring. Fluorescent lights and open-plan offices don't just annoy you, they flatten you. You have very particular interests that go very deep. You rehearse conversations before they happen and replay them for hours afterwards. Change feels physical, not just inconvenient.

If several of these ring bells, mention it to your GP or psychiatrist at your next review. Ask specifically: "Should I be assessed for autism in addition to ADHD?" The question is new enough in adult clinics that you may need to be the one who asks it.

What the 45 percent doesn't mean

It doesn't mean everyone with ADHD is secretly autistic. It means the overlap is much larger than the single-diagnosis model allowed for, and many adults have been living with half a map. Closing that gap — one conversation, one assessment, one accurate treatment plan at a time — is the work of the next decade.

Further reading

Taylor & Francis — Bibliometric analysis of co-occurrence of autism and ADHD. National Geographic — What is AuDHD?.