Autism vs ADHD: Why the Answer Is Often Both

You’ve read the autism checklist and the ADHD checklist, and you saw yourself in both. Maybe you’ve lived with one diagnosis for years and still feel like it only explains part of your life. It’s okay to not have all the answers right now, and you deserve a clearer picture than an online quiz can give you.

Your attention, your social instincts, and the way you take in sound and texture all grow out of the same developing brain, and many of the same genes shape them. A Swedish register study of nearly 1.9 million people found that autistic people had about 22 times the odds of also having ADHD, and that their relatives carried higher ADHD risk too. Telling the two apart takes precision about how your attention works, rather than how much of it you seem to have.

For decades, the standard was a single diagnosis. A 2022 clinical review notes that older editions of the main diagnostic manuals treated autism and ADHD as mutually exclusive, so a clinician had to pick one. That rule reflected how each condition was understood at the time, and the core features those manuals described still anchor each diagnosis today. The groundwork is real, and the science behind each diagnosis is well established.

But that either/or rule no longer matches the evidence, and at Siggy we’d rather help you describe your whole experience than squeeze it into one label.

Current criteria let a clinician diagnose both conditions when both are present. That matters because the overlap still gets missed: in a 2024 Spanish school study, only 15.8% of children who had both conditions had already been diagnosed with both. Looking at both is grounded in how brains develop, rather than in a trend toward more labels.

What This Page Covers

• What Is the Difference Between Autism and ADHD?
• Why Do Autism and ADHD Look So Similar?
• How Do Clinicians Tell Autism and ADHD Apart?
• Can You Have Both Autism and ADHD?
• Why Do Autism and ADHD Run Together?
• Do ADHD Medications Work Differently in Autism?
• Why Do Anxiety and Depression Matter So Much Here?
• How Siggy Fits In
• Start Your Anonymous Intake

What Is the Difference Between Autism and ADHD?

Autism and ADHD are both neurodevelopmental conditions, which means they begin in childhood and shape how your brain processes the world. Their core features are different.

A Lancet clinical seminar on autism describes it as early-appearing differences in social communication, along with repetitive sensory and motor behaviors. In daily life, that can look like finding unwritten social rules exhausting, needing routines to feel steady, or being overwhelmed by noise that others barely notice.

ADHD is defined by inattention, impulsivity, and hyperactivity that start in childhood and get in the way of daily life, according to an ADHD genetics review. The same review notes that about two-thirds of young people with ADHD still have impairing symptoms as adults.

Here’s how the two compare at a glance, drawing on the sources linked in this section and the sections below.

Feature	Autism	ADHD
Core Traits	Social communication differences, repetitive behaviors	Inattention, hyperactivity, impulsivity
Attention Pattern	Hard to shift focus	Short attention span, distractibility
Heritability Estimate	64% to 91%	About 74%
Response to Methylphenidate	Smaller on average, more side effects	Larger on average

The attention row comes from the 2022 clinical review above, the heritability figures from an autism twin meta-analysis and the ADHD genetics review, and the medication row from a controlled trial covered later in this guide.

Why Do Autism and ADHD Look So Similar?

Both conditions affect executive function, which is your brain’s ability to plan, switch between tasks, and hold information in mind. Both can also make social life harder. A 2019 psychiatry review describes these shared impairments while noting real differences in how they show up, enough to keep autism and ADHD as separate diagnoses.

Attention is where the confusion is sharpest. The 2022 clinical review notes that attention problems in autism tend to look like “not listening” or difficulty shifting focus, while ADHD looks more like a short attention span and easy distraction. If you’re autistic, you might lock onto something and find it hard to pull away. With ADHD, your focus might slide off anything that doesn’t grab you.

The traits also blend into each other. A 22-study ADHD meta-analysis found that children with ADHD scored substantially higher on measures of autistic traits than children without ADHD.

How Do Clinicians Tell Autism and ADHD Apart?

A good evaluation pulls together your developmental history, input from people who knew you as a child when that’s possible, and how your traits show up now. The goal is to understand why something is hard for you, since the same behavior can have different roots.

The traits that best separate the two may surprise you. An autism clinic study compared 55 autistic children with 27 children who had ADHD and 23 with anxiety disorders. Differences in communication and social connection, such as unusual or repetitive language and trouble building friendships, separated autism from ADHD. Repetitive behaviors and restricted interests did not separate the groups.

That study was small, involved only children, and used an older version of the criteria, so it isn’t the final word. It’s still a useful reminder that a checklist of quirks can’t make this call for you. If you’re an adult wondering about either condition, our guides to signs of autism in adults and getting an adult ADHD diagnosis walk through what an evaluation involves.

Can You Have Both Autism and ADHD?

Yes, you can have both, and it’s common. A 96-study autism meta-analysis found that 28% of autistic people also had ADHD. Looking the other way, the 22-study meta-analysis found that 21% of children with ADHD met criteria for autism.

You’ll see much higher and lower numbers online. The 2022 clinical review reports published rates ranging from 10% to 90%, depending on who was studied and how. In the 96-study meta-analysis, estimates from clinic samples ran higher than those from population studies.

People sometimes call the combination AuDHD. It’s an informal term rather than a diagnosis, and a clinician would record autism and ADHD as two conditions that occur together.

The bigger problem is that one condition often hides the other. In the Spanish school study, 32.8% of autistic children also had ADHD, yet only 15.8% of children with both had already been diagnosed with both. If one diagnosis has never felt like the whole story, that gap may be part of why.

Why Do Autism and ADHD Run Together?

Genes are a big part of the answer. The meta-analysis of autism twin studies estimated autism’s heritability at 64% to 91%, and the ADHD genetics review puts ADHD’s heritability at about 74%. Heritability describes how much of the variation in a population traces back to genes, and it doesn’t mean your path was fixed at birth.

The two conditions also share some of that genetic risk. In the Swedish register study, the link between autism in one twin and ADHD in the other was much stronger in identical twins than in fraternal twins or siblings. Identical twins share nearly all their DNA, so that pattern points to overlapping genetic roots rather than shared upbringing alone.

Do ADHD Medications Work Differently in Autism?

They can help, but the response tends to be smaller and side effects are more common. In a controlled methylphenidate trial in 72 autistic children with hyperactivity, 49% responded, while 18% stopped the medication because of side effects. The researchers found the benefit was smaller than what’s typical in children who have ADHD alone.

A 2021 medication meta-analysis of trials in people under 25 found that methylphenidate reduced hyperactivity and inattention in autistic young people, and atomoxetine, a non-stimulant, reduced inattention. The authors rated the quality of evidence as low to very low, and long-term data are thin.

Most of this research involves children, so adults have less to go on. Smaller average benefits and more side effects are reasons to adjust medication carefully and check in often, rather than reasons to rule it out. Our guide to stimulant vs non-stimulant ADHD medication explains how those two classes differ.

Why Do Anxiety and Depression Matter So Much Here?

Anxiety and depression are common alongside both conditions. The 96-study meta-analysis found pooled rates of 20% for anxiety disorders and 11% for depressive disorders among autistic people, and the ADHD genetics review notes that ADHD often co-occurs with mood and anxiety disorders.

That overlap matters day to day. When anxiety or low mood is part of the picture, it can be hard to tell which struggles come from which condition. Our guides to masking in autism and ADHD and ADHD and anxiety go deeper on both.

For many adults, anxiety or depression is the part that feels most urgent, and it’s often a practical place to start.

How Siggy Fits In

Siggy’s licensed prescribers diagnose and treat ADHD, autism-related concerns, anxiety, and depression, so the overlap can be looked at as one picture. Siggy can also help with the part that’s often hardest to say out loud.

The anonymous intake asks about mood, sleep, focus, and your history, with no name, email, or account. You’ll get a downloadable summary to keep or share with any clinician, so you don’t have to retell your story from scratch. A licensed prescriber reviews your full intake, including what you share about autistic or ADHD traits, before making a diagnosis or prescribing anything.

Siggy isn’t an emergency service. If you’re in crisis, call 911 or call or text 988. This article is for education only and isn’t a substitute for personal medical advice. It reflects sources available as of October 2026.

Start Your Anonymous Intake

If you’re in crisis right now, call 911 or call or text 988 first. If you’ve spent years wondering whether it’s autism, ADHD, or both, and anxiety or low mood is wearing you down, start your anonymous intake. It’s free, there’s no name or email required, and a licensed prescriber reviews your intake before anything is prescribed. Your summary is yours to keep and share with whoever helps you next.