Autism and ADHD Rarely Travel Alone: Common Co-Occurring Conditions and What the Research Shows

Autism and ADHD are often discussed as though each diagnosis exists by itself.

Clinically, that is frequently not what happens.

People with autism or attention-deficit/hyperactivity disorder often meet criteria for additional neurodevelopmental, psychiatric, sleep, learning, neurological, gastrointestinal, or other health conditions. Autism and ADHD also commonly occur with each other.

Researchers traditionally describe these additional diagnoses as comorbidities. Many neurodivergent people and clinicians instead use co-occurring conditions, particularly when discussing lifelong neurodevelopmental differences, because “comorbid” can imply that one condition is a complication of another.

Whatever language is used, the clinical point is the same:

Receiving an autism or ADHD diagnosis may identify one important piece of a considerably larger neurological and health profile.

That matters because symptoms can overlap. One condition can obscure another. And treating every difficulty as “just autism” or “just ADHD” can leave significant support needs unidentified.

Autism and ADHD commonly occur together

The relationship between autism and ADHD is one of the clearest examples.

A major systematic review and meta-analysis estimated ADHD in approximately 28% of autistic people, although estimates varied considerably across studies and populations. A population-based meta-analysis focused on autistic children and adolescents produced a similar estimate of about 26%.

The overlap can create a complicated internal experience.

Autism may involve a preference for predictability, repetition, sustained interests, or stable routines. ADHD may involve novelty seeking, inconsistent attention regulation, impulsivity, difficulty initiating tasks, or a need for stimulation.

A person can experience both.

The result may look contradictory from the outside: craving routine while struggling to maintain it, needing predictability while becoming restless with repetition, or being capable of extraordinary concentration in some circumstances while being unable to direct attention in others.

Those contradictions do not necessarily mean one diagnosis is incorrect.

Sometimes they are exactly what co-occurrence looks like.

Anxiety disorders

Anxiety is one of the most consistently reported mental-health conditions associated with both autism and ADHD.

The 2019 autism meta-analysis estimated anxiety disorders in approximately 20% of autistic participants overall. Research focused specifically on autistic adults estimated current anxiety disorders at approximately 27% and lifetime prevalence around 42%.

ADHD carries substantial anxiety overlap as well. A 2025 meta-analysis involving nearly 40,000 children and adolescents with ADHD estimated anxiety disorders in approximately 18.4% of participants. Among adults, large population studies indicate that anxiety disorders occur substantially more often in people with ADHD than in people without ADHD; one review calculated roughly five times the odds.

This overlap matters diagnostically because anxiety can also mimic or amplify neurodevelopmental symptoms.

An anxious person may become distracted. An overwhelmed autistic person may appear anxious. A person with ADHD may develop anxiety around years of forgetting, lateness, incomplete tasks, unpredictability, criticism, or repeated attempts to compensate for executive-function difficulties.

Symptoms can interact rather than remaining neatly separated.

Depression and mood disorders

Depression is also common.

The large autism meta-analysis estimated depressive disorders in approximately 11% of autistic people overall. Rates vary strongly with age; research focused specifically on autistic adults has reported considerably higher estimates, including approximately 23% current depression and 37% lifetime depression.

ADHD is similarly associated with elevated rates of depression and other mood disorders. Large-scale research comparing adults with and without ADHD has found substantially increased odds of major depressive disorder and bipolar disorder among adults with ADHD.

That does not mean ADHD or autism automatically causes depression.

Multiple pathways may matter: chronic stress, disability, social exclusion, repeated failure experiences, unmet support needs, sleep disruption, other psychiatric conditions, biological vulnerability, trauma, masking, and environmental demands.

The diagnosis establishes an association. It does not establish a single explanation.

Obsessive-compulsive disorder

OCD deserves particular attention because some of its outward behaviors can resemble autistic traits.

Repetition, rituals, strong routines, intense focus, distress around interruption, and repetitive thinking may occur in both autism and OCD. But they do not necessarily perform the same psychological function.

Autistic routines or interests may be comforting, regulating, enjoyable, organizing, or intrinsically meaningful. OCD compulsions are generally performed in response to intrusive thoughts, distress, fear, or uncertainty and are intended to prevent something feared or reduce anxiety—even when the person recognizes that the ritual may not rationally accomplish that goal.

A major autism meta-analysis estimated OCD in approximately 9% of autistic people. A 2024 systematic review focused on children and adolescents estimated OCD in approximately 11.6% of autistic youth. Looking in the opposite direction, approximately 9.5% of youth samples with OCD had autism.

That bidirectional overlap is clinically important.

A behavior that gets automatically attributed to autism may sometimes be OCD. A behavior assumed to be compulsive may instead be a preferred autistic routine. And one person can have both.

Sleep disorders

Sleep problems are common across both autism and ADHD.

Large autism reviews identify sleep-wake problems among the most frequent co-occurring conditions. ADHD clinical guidance likewise recommends screening for sleep disorders and sleep apnea because sleep problems can coexist with ADHD and can also produce symptoms that resemble it.

Sleep also complicates diagnosis.

Insufficient or fragmented sleep can worsen attention, memory, emotional regulation, executive functioning, irritability, sensory tolerance, and impulse control.

In other words, sleep problems can both co-occur with neurodivergence and intensify the very symptoms used to evaluate it.

Learning, language and developmental conditions

Neurodevelopmental diagnoses frequently cluster.

ADHD commonly occurs alongside specific learning disorders, language disorders, autism, motor difficulties, and other developmental conditions. Current CDC clinical guidance specifically recommends screening people with ADHD for developmental conditions such as learning and language disorders and autism.

Autistic people may also have intellectual disability, language differences, developmental coordination disorder, or learning disabilities. A large 2023 systematic review of approximately 590,000 autistic children and adults identified developmental coordination disorder among the most frequent co-occurring conditions studied.

This is one reason a single diagnostic label may not adequately explain a person’s school history.

Difficulty with reading, written expression, mathematics, motor coordination, language processing, working memory, or executive functioning deserves assessment on its own rather than automatically being attributed to autism or ADHD.

Tic disorders, disruptive behavior and related diagnoses

ADHD commonly co-occurs with tic disorders and disruptive-behavior diagnoses.

The CDC identifies tic disorders and disruptive behavior disorders among common conditions clinicians should consider when assessing ADHD. A 2025 meta-analysis of children and adolescents with ADHD estimated oppositional defiant disorder at approximately 34.7%, broader behavior disorders at 30.7%, and conduct disorder at approximately 10.7%.

These categories require particular care in interpretation.

Behavior labels describe patterns clinicians observe. They do not automatically explain why a behavior is occurring.

Communication difficulties, sensory overload, trauma, impulsivity, frustration, inaccessible environments, unmet accommodations, anxiety, sleep deprivation, learning difficulties, and genuine disruptive-behavior disorders can produce overlapping outward presentations.

Differential diagnosis matters.

Epilepsy and seizure disorders

Epilepsy is particularly important in autism.

Systematic reviews of autism comorbidity repeatedly identify epilepsy as an important neurological co-occurring condition. This belongs in the conversation because neurodivergence is often treated exclusively as a psychiatric or behavioral topic.

It is not.

Autism in particular can exist within a much broader neurological profile.

Gastrointestinal conditions

Gastrointestinal symptoms are also repeatedly reported among autistic populations.

Large systematic reviews identify gastrointestinal problems among the most frequent co-occurring conditions reported in autism research.

This does not mean gastrointestinal problems cause autism. Nor does it validate unsupported claims that treating the gastrointestinal system will “cure” autism.

It means gastrointestinal health is a legitimate part of healthcare for autistic people and should not be dismissed simply because the patient is autistic.

Eating and feeding disorders

Eating difficulties occupy another important intersection.

Autistic sensory sensitivities, preference for sameness, restricted food repertoires, interoceptive differences, and feeding difficulties can overlap with clinically recognized feeding and eating disorders. The 2023 autism review identified feeding and eating disorders among the more common categories of co-occurring conditions.

ADHD is also associated with eating disorders. A meta-analysis found that people with ADHD had significantly higher odds of receiving an eating-disorder diagnosis than people without ADHD.

The relationships are heterogeneous and cannot be reduced to one mechanism.

Substance-use disorders

Substance-use disorders become particularly relevant in ADHD research during adolescence and adulthood.

Reviews of adult ADHD consistently identify substance-use disorders among important psychiatric co-occurring conditions. Large population studies have found substantially higher odds of substance-use disorders among adults with ADHD than among adults without ADHD.

Again, association should not be converted into destiny.

Most people with ADHD do not inevitably develop a substance-use disorder. The research instead supports treating substance use as an important area to assess rather than assuming it is unrelated to the person’s neurodevelopmental profile.

Physical health belongs in the conversation too

The research literature increasingly makes clear that ADHD should not be treated purely as a concentration disorder and autism should not be treated purely as a social-communication diagnosis.

A 2024 umbrella review examined 76 psychiatric, physical, and behavioral conditions across more than 234 million participants in ADHD research. The strongest evidence linked ADHD with several neuropsychiatric conditions as well as night awakenings, obesity, asthma, several vision conditions, and suicidal ideation. Moderate-certainty evidence also supported associations with headache, mood and affective disorders, depression, fractures, atopic rhinitis, suicide attempts, suicide mortality, and all-cause mortality.

This does not mean every condition on such a list is directly caused by ADHD.

Umbrella reviews identify statistical relationships. They also reveal how incomplete healthcare becomes when clinicians examine the brain while ignoring the rest of the body.

One diagnosis should not become a diagnostic stopping point

This may be the most important practical conclusion.

Once a person receives an autism or ADHD diagnosis, there is a risk that every subsequent difficulty gets interpreted through that diagnosis.

Poor sleep becomes “the ADHD.”

Severe anxiety becomes “the autism.”

Compulsive behavior becomes “just rigidity.”

Reading difficulty becomes “attention problems.”

Gastrointestinal complaints become irrelevant to a behavioral-health appointment.

Depression becomes burnout. Burnout becomes depression.

Sensory avoidance around food becomes assumed pickiness.

A seizure-like event gets interpreted as unusual behavior.

This is one reason careful differential diagnosis matters.

A known neurodevelopmental diagnosis should provide more context for assessment—not become a reason to stop assessing.

Co-occurring conditions can also hide the original diagnosis

The reverse problem happens too.

Sometimes anxiety is identified years before autism. Depression may be treated before ADHD is recognized. OCD may dominate the clinical picture. A learning disorder may explain school difficulties well enough that nobody investigates broader executive-function problems.

A person may accumulate several diagnoses while the underlying neurodevelopmental pattern remains unidentified.

That may be especially relevant for adults whose autism or ADHD was missed during childhood.

A late diagnosis does not necessarily mean the neurodevelopmental condition suddenly appeared.

It may mean clinicians finally recognized a pattern that had previously been divided among several other explanations.

The question after diagnosis should be larger than “What do I have?”

Autism and ADHD are heterogeneous.

Two autistic people can have dramatically different medical, developmental, and psychiatric profiles. Two people with ADHD can require completely different supports. Two AuDHD people can share both diagnoses and still have very different experiences because the rest of their diagnostic picture is different.

The more useful question may become:

What combination of neurological, psychological, developmental, and physical conditions is shaping this particular person’s functioning?

That question leaves room for autism. ADHD. OCD. Anxiety. Depression. Learning disabilities. Sleep disorders. Eating disorders. Epilepsy. Gastrointestinal problems. Tics. Substance-use disorders. And other conditions that require evaluation in their own right.

A diagnosis can provide language for one part of a person’s experience.

Sometimes it also creates enough clarity to notice the other parts.

What the evidence allows us to say

Research strongly supports the conclusion that autism and ADHD frequently occur alongside other diagnoses and health conditions.

Anxiety, depression, and sleep problems appear prominently in both literatures. Autism and ADHD frequently occur together. Learning and developmental disorders are important across both populations. OCD has a meaningful association with autism. Epilepsy and gastrointestinal conditions are particularly established concerns in autism research. Behavior disorders, tic disorders, and substance-use disorders are important components of ADHD assessment. Eating and feeding difficulties intersect with both.

And medical conditions should not be excluded merely because a person already has a neurodevelopmental diagnosis.

What the evidence does not allow us to say

Co-occurrence is not causation.

Having autism does not mean a person will develop every condition statistically associated with autism. Having ADHD does not make anxiety, depression, addiction, or an eating disorder inevitable. A symptom shared by two conditions cannot establish which diagnosis explains it. Population prevalence cannot diagnose an individual. And an online list of “conditions that go with autism or ADHD” cannot substitute for a clinical differential assessment.

Those boundaries are important because neurodivergent people are especially vulnerable to having symptoms either overpathologized or prematurely explained away.

Good assessment avoids both.

Scholarly Integrity Statement

This resource describes conditions that occur at elevated rates alongside autism and/or ADHD. Statistical association does not establish that autism or ADHD causes the associated condition.

Prevalence estimates vary substantially according to age, sex, intellectual disability, diagnostic criteria, study design, clinical versus community sampling, and method of assessment. Estimates from different studies should therefore not be interpreted as universal rates applicable to every autistic or ADHD population.

The terms co-occurring condition and comorbidity are used to describe diagnoses or health conditions present in the same individual. Their presence requires independent clinical assessment.

This resource is educational and does not substitute for individualized medical, psychological, or psychiatric evaluation.

References

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Hollocks, M. J., Lerh, J. W., Magiati, I., Meiser-Stedman, R., & Brugha, T. S. (2019). Anxiety and depression in adults with autism spectrum disorder: A systematic review and meta-analysis. Psychological Medicine, 49(4), 559–572.

Hossain, M. M., et al. (2023). Prevalence of co-occurring conditions in children and adults with autism spectrum disorder: A systematic review and meta-analysis. Neuroscience & Biobehavioral Reviews, 155, 105436.

Aymerich, C., et al. (2024). Prevalence and correlates of the concurrence of autism spectrum disorder and obsessive compulsive disorder in children and adolescents: A systematic review and meta-analysis. Brain Sciences, 14(4), 379.

Njardvik, U., Wergeland, G. J., Riise, E. N., Hannesdottir, D. K., & Öst, L.-G. (2025). Psychiatric comorbidity in children and adolescents with ADHD: A systematic review and meta-analysis. Clinical Psychology Review, 118, 102571.

Arrondo, G., et al. (2024). Comorbid health conditions in people with attention-deficit/hyperactivity disorders: An umbrella review of systematic reviews and meta-analyses.

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Centers for Disease Control and Prevention. (2026). Other Concerns and Conditions with ADHD.

Centers for Disease Control and Prevention. (2026). Clinical Care of ADHD in Children.