ADHD and autism overlap to a striking degree. Somewhere between half and 70% of autistic people also meet criteria for ADHD, and a substantial share of people with ADHD show autistic traits that fall short of a formal diagnosis.1PubMed Central. ASD and ADHD Comorbidity: What Are We Talking About? Until 2013, the official diagnostic manual actually prohibited giving someone both diagnoses at the same time, treating them as mutually exclusive. That changed with the DSM-5, and the research that followed has painted a picture of two conditions that share genetics, brain wiring, cognitive patterns, and everyday struggles in ways that make the boundary between them blurry at the edges.
How Often the Two Conditions Co-Occur
The co-occurrence rate is not a small footnote. Multiple reviews converge on the figure that 50 to 70% of people with autism also have clinically significant ADHD symptoms.2PubMed Central. ASD and ADHD Comorbidity: What Are We Talking About? Going the other direction, estimates of autistic traits in ADHD populations are lower but still well above what you’d expect by chance. This is not merely a matter of symptom overlap leading to double-counting. Structured diagnostic interviews that carefully separate the two conditions still find high rates of genuine co-occurrence. The people who have both, sometimes called “AuDHD” in online communities, often describe their experience as qualitatively different from having either condition alone.
Shared Genetic Roots
Family and twin studies consistently show that ADHD and autism draw from a partly shared genetic pool.3PubMed Central. Shared heritability of attention-deficit/hyperactivity disorder and autism spectrum disorder Both conditions are highly heritable on their own, and when one appears in a family, the other shows up more often than it does in the general population. This is not a single “overlap gene” at work. Research on families where both conditions co-occur has found that shared genetic risk concentrates in biological pathways involved in how brain cells grow and connect, including pathways related to the tiny hair-like structures on cells called cilia, to ion channels that help nerve cells communicate, and to the chemical packaging of DNA that controls which genes get turned on.4PubMed Central. Common genetic risk factors in ASD and ADHD co-occurring families In other words, the overlap is happening deep in the machinery of brain development, not at the level of any one gene doing double duty.
What the Brain Looks Like in Each Condition
Brain imaging studies reveal a complicated picture: some features are unique to each condition and some are shared. In broad strokes, autism tends to be associated with increased total brain volume, while ADHD tends to be associated with decreased volume. The amygdala, a region involved in processing emotions and threat, tends to be larger in autism but looks typical in ADHD. But certain structures show strikingly similar patterns in both conditions. The corpus callosum, which connects the brain’s two hemispheres, and the cerebellum, which coordinates movement and some aspects of cognition, tend to be smaller in both.5PubMed. A Comparison of Structural Brain Imaging Findings in Autism Spectrum Disorder and Attention-Deficit Hyperactivity Disorder
A large-scale analysis that charted brain anatomy across thousands of individuals found that when someone has both autism and ADHD, their brain does not simply look like a blend of the two. Instead, the combination produces its own unique pattern: widespread increases in cortical thickness along with reductions in surface area that differ from what either condition shows alone.6PubMed Central. Brain-charting autism and attention deficit hyperactivity disorder reveals distinct and overlapping neurobiology That same study found that sex influenced the brain anatomy of autism but not ADHD, and that age had a stronger relationship to brain changes in ADHD than in autism. These kinds of findings suggest the co-occurring condition is not just “autism plus ADHD” stacked on top of each other. It may have its own neurobiology.
Executive Function and the Thinking Overlap
Executive functions are the mental skills that let you plan, switch between tasks, hold things in working memory, and stop yourself from acting impulsively. Both ADHD and autism are associated with trouble in these areas, but the specific pattern of difficulties differs in instructive ways. A review of the evidence found that people with autism tend to struggle most with flexibility (shifting from one task or idea to another) and planning, while people with ADHD struggle most with response inhibition, the ability to stop a prepotent response.7PubMed Central. A review of executive function deficits in autism spectrum disorder and attention-deficit/hyperactivity disorder People with both conditions appear to carry both patterns of difficulty, suggesting the co-occurrence is additive rather than creating some new category of impairment.
Yet a meta-analysis comparing the two groups head-to-head found no significant differences in overall executive function performance between people with ADHD and people with autism. Both groups performed worse than neurotypical people across attention, flexibility, working memory, processing speed, and response inhibition.8PubMed Central. Do ASD and ADHD Have Distinct Executive Function Deficits? A Systematic Review and Meta-Analysis of Direct Comparison Studies This may sound contradictory, but it points to the challenge clinicians face: the two conditions look different when you zero in on narrow subtypes of executive function, yet remarkably similar when you measure them with broad tests. A single score on a working memory test, for example, is not going to tell you which condition the person has.
Social Difficulties Look Different Up Close
Both ADHD and autism involve social challenges, but the nature of those challenges is different in ways that matter for everyday life and for treatment. Research comparing children with each condition found that autistic children tend to lack adaptive social skills, meaning they struggle with the underlying knowledge of how social interactions work: reading facial expressions, understanding conversational turn-taking, picking up on social norms. Children with ADHD, by contrast, generally possess that social knowledge but fail to apply it. Their social difficulties stem from impulsive or intrusive behavior, not from a gap in understanding.9Research in Autism Spectrum Disorders. Comparing social skill profiles of children with autism spectrum disorders versus children with attention deficit hyperactivity disorder: Where the deficits lie
A useful way to think about this: an autistic child might not notice that a peer is bored with a conversation, while a child with ADHD might notice but blurt out something off-topic before they can adjust. Both end up struggling to maintain friendships, but for very different reasons.10PubMed Central. Common outcome, different pathways: Social information-processing deficits in autism spectrum disorder and attention-deficit/hyperactivity disorder For people who have both conditions, the picture gets harder to untangle. The social knowledge gap and the impulsivity-driven performance gap compound each other, making the combined presentation look more severe than either alone.
Sensory Processing
Sensory sensitivities are a hallmark of autism, but they show up in ADHD far more often than most people realize. Studies comparing the two groups find that children with either condition have elevated rates of atypical sensory processing compared to typically developing children, and the overall levels of sensory difficulty are often comparable between the two groups.11PubMed. Sensory Processing Patterns in Autism, Attention Deficit Hyperactivity Disorder, and Typical Development Research from the ELENA cohort similarly found that atypical sensory processing was more frequent in both conditions than in typical development, without a significant difference between the ADHD and autism groups.12PubMed. Sensory processing related to attention in children with ASD, ADHD, or typical development: results from the ELENA cohort
Where differences do emerge is in specific sensory domains. Autistic children tend to show the highest rates of oral processing differences, things like extreme food texture preferences or chewing on non-food objects. Children with ADHD tend to show more atypical visual processing.13PubMed. Sensory Processing Patterns in Autism, Attention Deficit Hyperactivity Disorder, and Typical Development Another study using detailed sensory profiles found that while autism and ADHD differed from each other on most sensory subscales, they were indistinguishable on unresponsiveness, auditory filtering, and visual/auditory processing.14Middle East Current Psychiatry. Sensory processing patterns among children with autism spectrum disorder (ASD) and attention deficit hyperactivity disorder (ADHD) using short sensory profile and evoked potentials: a case–control study The takeaway is that sensory overload is not a reliable way to distinguish between the two conditions. If you are overwhelmed by loud restaurants and scratchy clothing tags, that tells you something about your nervous system, but it doesn’t point clearly to one diagnosis over the other.
Hyperfocus and Inattention as a Shared Pattern
Hyperfocus is one of the most discussed features in ADHD communities, the ability to lock onto a task so completely that hours vanish. But deep, absorptive attention to interests is also central to the autistic experience. Research investigating this overlap found that hyperfocus and inattention were elevated in all neurodivergent groups compared to neurotypical adults, and the two were positively correlated: the more someone experienced hyperfocus, the more they also experienced inattention. This suggests that atypical regulation of attention, swinging between locked-in and scattered, is a shared feature rather than something that belongs exclusively to either condition.
Sleep Problems in Both Conditions
Sleep disturbances are common enough in both ADHD and autism that they are almost a shared symptom, yet the specific sleep difficulties differ. Adults with ADHD are more prone to periodic limb movements during sleep, the involuntary leg jerks that disrupt rest, while autistic adults tend to spend more time in the lightest stage of sleep.15PubMed Central. Management of sleep disorders in autism spectrum disorder with co-occurring attention-deficit hyperactivity disorder: update for clinicians In children, those with both autism and ADHD show greater motor activity during sleep than children with either condition alone. Research tracking wrist temperature, a marker closely tied to melatonin and the body’s internal clock, found an atypical pattern in autistic children that was even more pronounced in those with co-occurring ADHD, supporting the idea of a shared disruption in the body’s circadian timing system.16PubMed. Sleep problems and circadian rhythm functioning in autistic children, autism with co-occurring attention deficit hyperactivity disorder, and typically developing children: A comparative study
For people living with both conditions, sleep problems can amplify daytime difficulties in attention, emotional regulation, and sensory sensitivity. Addressing sleep is one of the first practical recommendations in expert consensus guidelines for co-occurring ADHD and autism.17PubMed Central. Guidance for identification and treatment of individuals with attention deficit/hyperactivity disorder and autism spectrum disorder based upon expert consensus
How the Overlap Changes Across a Lifetime
The relationship between ADHD and autistic traits is not static. A longitudinal study tracking people from childhood into early adulthood identified three trajectories: a large majority with low, stable levels of both trait types; a male-predominant group whose ADHD and autistic traits declined through childhood and adolescence; and a group whose traits emerged later.18PubMed Central. Co‐development of attention deficit hyperactivity disorder and autistic trait trajectories from childhood to early adulthood The correlation between ADHD traits and autistic traits was strongest in young adulthood for the non-typically-developing groups, meaning the two conditions became more intertwined over time, not less.
A separate review proposed that the co-occurrence of ADHD and autism peaks during adolescence, possibly because that period demands the highest levels of social adaptation and executive function skill, the exact areas both conditions affect.19PubMed. Changing ASD-ADHD symptom co-occurrence across the lifespan with adolescence as crucial time window: Illustrating the need to go beyond childhood The practical implication is important: if you were assessed as a child and received only one diagnosis, the other condition may become more apparent as social and occupational demands increase in adolescence or adulthood.
Why Diagnosis Gets Especially Complicated for Women
Both autism and ADHD are historically underdiagnosed in women and girls, and the co-occurring presentation makes this problem worse. Qualitative research with women who received dual diagnoses in adulthood reveals how deeply gender norms shape the diagnostic process. Women described being expected to be socially attuned and organized, and when they struggled in those areas, the difficulties were attributed to personality or mental health problems rather than neurodevelopment.20PubMed Central. Being a Woman Is 100% Significant to My Experiences of Attention Deficit Hyperactivity Disorder and Autism The brain imaging research mentioned earlier also found that sex modulates the neuroanatomy of autism specifically, meaning the biological presentation itself may look different in women, not just the social expression.21PubMed Central. Brain-charting autism and attention deficit hyperactivity disorder reveals distinct and overlapping neurobiology
Camouflaging, the conscious or unconscious effort to appear neurotypical, adds another layer. Research comparing camouflaging in adults with ADHD, autism, and a comparison group found that adults with ADHD scored higher on camouflaging measures than the comparison group, though not as high as autistic adults.22PubMed. Is camouflaging unique for autism? A comparison of camouflaging between adults with autism and ADHD Autism traits, rather than ADHD traits, were the stronger predictor of camouflaging behavior regardless of diagnosis. For women who camouflage extensively, the cognitive and emotional cost is substantial, and the masking can delay accurate diagnosis by years or decades.
Telling the Two Apart on a Screening Form
Given all of this overlap, you might wonder whether screening tools can actually separate the two conditions. Research using a 30-item autism checklist found that autistic children scored a mean of 22 out of 30, while children with ADHD scored a mean of 4, a very clean separation on autism-specific items.23Research in Autism Spectrum Disorders. Autism and ADHD: Overlapping and discriminating symptoms Three of the 30 autism symptoms appeared only in autistic children, never in those with ADHD. Going the other direction, however, ADHD symptoms were common in autism: children with autism and children with ADHD-combined type did not differ on parent ratings of inattention, impulsivity, and hyperactivity. On neuropsychological tests measuring attention, working memory, and processing speed, the groups were also indistinguishable.
The practical lesson: autism-specific tools can identify autism, and the core features of autism remain distinctive. But ADHD symptoms are very poor at discriminating between the two conditions because they appear so frequently in autistic people. If you score high on an ADHD checklist, that does not rule out autism. If you score low on an autism screener, it probably does rule out autism, since the autism-specific items are quite discriminating.
Medication When Both Conditions Are Present
Treating ADHD in someone who is also autistic used to be considered risky. Clinicians worried that stimulant medications would worsen irritability, anxiety, or repetitive behaviors. The evidence has caught up and paints a more reassuring picture. A meta-analysis of pharmacological interventions found that methylphenidate (the active ingredient in drugs like Ritalin and Concerta) improved hyperactivity, irritability, and inattention in autistic people compared to placebo. It did not affect repetitive behaviors. However, side effects led to a higher dropout rate than in typical ADHD trials, suggesting that autistic individuals may be more sensitive to adverse effects.24Progress in Neuro-Psychopharmacology and Biological Psychiatry. Effectiveness of pharmacological interventions for managing ADHD symptoms in individuals with autism spectrum disorder: A systematic review and meta-analysis Atomoxetine, a non-stimulant, also showed positive effects on hyperactivity and inattention without the same dropout problem.
A study comparing adults with ADHD alone to adults with ADHD plus autism found that both groups experienced significant decreases in ADHD symptoms on medication, and the autism diagnosis did not reduce how well the medication worked. Side effect profiles were similar between the groups.25PubMed Central. Pharmacotherapy of ADHD in Adults With Autism Spectrum Disorder: Effectiveness and Side Effects The upshot is that ADHD medication is worth trying even when autism is present, but starting at lower doses and monitoring closely for side effects is a reasonable approach given the higher sensitivity some autistic people report.
Beyond Medication
Expert consensus guidelines for co-occurring ADHD and autism recommend a multi-layered approach that goes well beyond prescriptions. Recommendations include psychoeducation (helping the person and their family understand both conditions), carer training, behavioral strategies, cognitive behavioral therapy adapted for neurodevelopmental differences, and multi-agency coordination covering education, career guidance, and occupational skills.26PubMed Central. Guidance for identification and treatment of individuals with attention deficit/hyperactivity disorder and autism spectrum disorder based upon expert consensus Social skills therapy, individual and family psychotherapy, and behavioral interventions are all considered beneficial for co-occurring presentations.27PubMed. Co-occurrence of ADHD and autism spectrum disorders: phenomenology and treatment
One area that gets less clinical attention but comes up constantly in lived-experience reports is environmental design. Reducing sensory overload, creating predictable routines, and structuring tasks into smaller steps can address difficulties common to both conditions simultaneously. These strategies are not glamorous, but for people living with both ADHD and autism, modifying the environment often does more day-to-day good than any single intervention.
The Dopamine Connection
ADHD is strongly associated with differences in the dopamine system, the brain’s signaling network involved in motivation, reward, and attention. Research has found that dopamine-related gene variants also play a role in autism, particularly in modulating emotional dysregulation and ADHD-like symptoms within autistic individuals. Variants in the dopamine transporter gene and a dopamine receptor gene were associated with parent-rated hyperactivity, teacher-rated inattention, and emotional difficulties like anxiety and depression in autistic children.28PubMed Central. Association of dopamine gene variants, emotion dysregulation and ADHD in autism spectrum disorder This suggests the dopamine system may be one of the specific biological routes through which the two conditions intersect. It also helps explain why stimulant medications, which primarily boost dopamine signaling, can help ADHD symptoms in autistic people.
Motor Coordination and Physical Overlap
Motor clumsiness doesn’t show up in the diagnostic criteria for either condition, but it is remarkably common in both. Developmental coordination disorder, which involves significant difficulty with motor skills, was diagnosed in a quarter of school-age girls with autism, about a third of those with ADHD, and a striking 80% of preschool-age girls with autism in one clinical sample.29PubMed. Developmental coordination disorder and other motor control problems in girls with autism spectrum disorder and/or attention-deficit/hyperactivity disorder The high rates in both conditions point again to shared differences in how the developing brain organizes complex tasks.
Another physical feature that bridges the two conditions is joint hypermobility. A study found that generalized joint hypermobility was roughly four and a half times more common in autistic individuals and about four and a third times more common in those with ADHD compared to the general population.30PubMed Central. Joint Hypermobility Links Neurodivergence to Dysautonomia and Pain Hypermobility in turn was linked to greater orthostatic intolerance symptoms (dizziness on standing, racing heart) and musculoskeletal pain. These connections between neurodevelopmental conditions and connective tissue features are not well understood yet, but they suggest the overlap between ADHD and autism extends beyond the brain into the body more broadly. If you have one or both conditions and deal with unexplained joint pain or episodes of dizziness, this line of research may be worth raising with your doctor.