ADHD and autism are comorbid, and they co-occur at remarkably high rates. Between 50 and 70% of people with autism also meet the criteria for ADHD, making it one of the most common overlapping pairs in neurodevelopmental conditions. The two share genetic roots, overlapping brain features, and similar challenges with executive function and sensory processing, yet they remain distinct conditions with different core profiles.
How Often They Co-Occur
The overlap between ADHD and autism is far more common than chance alone would predict. Studies consistently place the rate of ADHD among autistic individuals at 50 to 70%, though some estimates range as wide as 10 to 90% depending on the population studied and the diagnostic tools used. The relationship runs in both directions: people with ADHD are also diagnosed with autism at elevated rates compared to the general population.
Before 2013, clinicians were not permitted to diagnose both conditions in the same person. The fourth edition of the Diagnostic and Statistical Manual (DSM-IV) treated ADHD and autism as mutually exclusive, meaning if you had an autism diagnosis, you couldn’t officially receive an ADHD diagnosis on top of it. The DSM-5, published in 2013, removed that restriction and allowed dual diagnosis for the first time. That single change opened the door for millions of people to receive a more complete clinical picture.
Shared Genetics
Both ADHD and autism are highly heritable. Family and twin studies estimate that genetic factors account for roughly 70 to 80% of the variation in each condition, and a significant portion of those genetic influences are shared between the two. In other words, some of the same genes that increase the likelihood of autism also increase the likelihood of ADHD.
Large-scale genome studies have started pinpointing specific genetic variants linked to both conditions. One gene of particular interest is SHANK2, which plays a role in how brain cells communicate at their connection points. Researchers found six genetic variants within SHANK2 that were significantly associated with both ADHD and autism, three of which held up under rigorous statistical correction. SHANK2 is now considered a pleiotropic gene for the two conditions, meaning it influences both through a shared biological pathway.
What Happens in the Brain
Brain imaging research has identified structural features common to both conditions. A key area of overlap is the anterior cingulate cortex and its connections to other regions in the front of the brain. These areas are central to cognitive control (the ability to focus, plan, and regulate impulses) and social-emotional functioning, both of which are affected in ADHD and autism. Differences in how these regions thin and develop over time may help explain why some people develop primarily ADHD traits, primarily autistic traits, or both.
Studies in adolescents have also found that both conditions involve reduced gray matter in parts of the brain involved in memory and emotional processing, alongside increases in a region of the parietal cortex tied to attention and spatial awareness. These overlapping patterns suggest that ADHD and autism are not just behaviorally similar in some respects but share roots in how the brain is physically organized.
Executive Function Differences
Executive function is the umbrella term for the mental skills that let you plan, stay focused, remember instructions, and switch between tasks. Deficits in executive function show up in both ADHD and autism, sometimes as early as preschool, but the specific profile differs between the two.
In ADHD, the core executive function problems center on inhibition and sustained attention. Difficulty suppressing impulses and maintaining focus drives the hallmark symptoms of hyperactivity and inattention. In autism, executive function challenges tend to show up more in cognitive flexibility, the ability to shift thinking when rules or expectations change. Both conditions affect working memory, the capacity to hold and manipulate information in the moment, but executive function deficits are generally more pronounced in ADHD. When someone has both conditions, these difficulties tend to compound, creating a more complex profile than either condition alone would produce.
Sensory Processing
Atypical responses to sensory input are a feature of both conditions, though they tend to look different. Up to 95% of autistic individuals experience atypical sensory processing, and about 66% of children with ADHD do as well. When both conditions are present, sensory challenges become even more pronounced than in either condition on its own.
The distinction lies in direction. Autistic individuals more commonly display sensory avoidance: pulling away from bright lights, loud sounds, or certain textures because their nervous system reacts intensely to stimulation. People with ADHD, by contrast, tend toward sensory seeking. Their nervous systems may be under-activated, leading them to crave strong sensory input as a way to maintain alertness. Hyperactivity itself may partly be a compensatory response, a way for the body to generate the stimulation the brain needs.
Children with both ADHD and autism show a particularly complex sensory pattern. In one study, the combined group displayed more severe sensory avoidance than children with autism alone and more avoidance than children with ADHD alone. They also scored higher on atypical sensory processing across nearly every category measured, suggesting that the two conditions interact to amplify sensory difficulties rather than simply adding them together.
Social Challenges Look Different Up Close
Both ADHD and autism can cause significant social difficulties, but the underlying reasons are distinct. In autism, social challenges stem from differences in social cognition: difficulty reading facial expressions, interpreting tone of voice, or understanding unspoken social rules. This can lead to social disengagement, isolation, or apparent indifference to conversational cues.
In ADHD, social problems are typically driven by impulsivity and inattention. A child with ADHD might interrupt constantly, miss social cues because they weren’t paying attention, or struggle to take turns in conversation. The desire to connect socially is usually intact, but the execution falls short. Peer rejection in ADHD looks different from the social withdrawal more characteristic of autism, and clinicians use this distinction when determining whether someone has one condition, the other, or both. When the two co-occur, teasing apart which symptoms come from which condition becomes genuinely difficult, both for clinicians and for the individuals themselves.
Why Diagnosis Often Gets Delayed
When ADHD and autism co-exist, the path to a complete diagnosis is often long. Children who receive their ADHD diagnosis first are diagnosed with autism an average of three years later than children whose autism is identified at the same time or before their ADHD. Even more strikingly, children diagnosed with ADHD first are 30 times more likely to receive their autism diagnosis after age six.
This pattern likely reflects the fact that ADHD symptoms, particularly hyperactivity and impulsivity, tend to be more visible and disruptive in early childhood, drawing clinical attention first. Autistic traits like difficulty with social reciprocity or rigid thinking patterns may be attributed to the ADHD or overlooked entirely until the child is older and social demands increase. For many people, especially those diagnosed in adolescence or adulthood, the autism component goes unrecognized for years.
How Treatment Differs With Both Conditions
One common concern for people with both conditions is whether ADHD medications will work or cause problems. Research has been reassuring on this front. In studies comparing stimulant medication response, children with both autism and ADHD showed statistically significant improvements in hyperactivity, impulsivity, inattention, oppositionality, and aggression that were comparable to improvements seen in children with ADHD alone. There was no significant difference in the degree of improvement between the two groups.
Side effects also differed in an interesting way. Children with ADHD alone experienced nausea, dizziness, headaches, and sleep difficulties on stimulant medication. Children with both autism and ADHD reported sleep difficulties as the only notable side effect. Importantly, stimulant treatment did not worsen tics or repetitive behaviors in either group, which had been a longstanding concern for clinicians treating autistic individuals with ADHD medication.
That said, medication addresses only the ADHD component. The social communication differences, sensory sensitivities, and cognitive inflexibility associated with autism typically require separate support, often through behavioral strategies, occupational therapy for sensory challenges, or structured social skills work. Getting both diagnoses right matters because it shapes the full scope of support someone receives.