How common is co-occurrence?
The evidence for co-occurrence between ADHD and autism is now substantial. A 2021 meta-analysis found that approximately 50 to 70 percent of autistic individuals also meet criteria for ADHD, and approximately 20 to 50 percent of people with ADHD also meet criteria for autism. These figures vary by population, study methodology, and diagnostic threshold, but the direction is consistent: the two conditions co-occur at rates far above what chance would predict.
Genome-wide association studies have also found significant genetic overlap between the two conditions, suggesting shared biological substrates. This is not simply a matter of diagnostic criteria overlapping: there appear to be genuine neurobiological reasons why people who have one of these conditions have elevated rates of the other.
Why they were historically kept separate
Prior to the publication of DSM-5 in 2013, the diagnostic criteria explicitly excluded a diagnosis of ADHD in the presence of autism. A clinician who diagnosed autism could not, under the prevailing framework, also diagnose ADHD, even when ADHD symptoms were clearly present and clearly causing additional impairment beyond what the autism alone would explain.
The rationale for this exclusion was largely theoretical: it was assumed that the attentional and behavioural difficulties seen in autistic individuals were better attributed to autism than to a separate ADHD process. As the evidence for genuine co-occurrence accumulated, this position became increasingly difficult to sustain, and DSM-5 removed the exclusion criterion. Both diagnoses can now be made in the same person.
The practical consequence of those decades of exclusion is that a significant number of adults who were diagnosed with autism before 2013 have never been assessed for ADHD, and may have ADHD-specific difficulties that remain unaddressed. Similarly, many adults diagnosed with ADHD have never been assessed for autism, and may have autistic features that explain aspects of their experience that ADHD alone does not account for.
Overlap and differences between the conditions
ADHD and autism share a number of surface features that can make distinguishing them clinically challenging, particularly in adults who have had decades to develop compensatory strategies. Both conditions involve executive function difficulties, including problems with organisation, task initiation, and working memory. Both involve difficulties in social contexts. Both often involve heightened sensory sensitivity. Both are associated with intense focused interests in specific topics or activities.
The underlying reasons for these shared features differ significantly, however. The social difficulties in ADHD typically arise from impulsivity, inattention, and emotional dysregulation: the person wants to connect but struggles to manage the interaction effectively. In autism, social difficulties more often arise from differences in social communication style and processing: the person may experience social interaction as genuinely confusing or exhausting in ways that are distinct from ADHD-related social struggles.
The attentional picture also differs. ADHD attention is novelty-seeking and context-sensitive: intense where something is interesting, absent where it is not. Autistic attention tends toward depth and consistency rather than breadth and novelty: the characteristic hyperfocus on specific interests is different in quality from ADHD hyperfocus, and the two can produce similar-looking behaviour through different mechanisms.
"Many adults describe their experience as neither condition fully explaining it. When both are present, neither diagnosis alone gives a complete account of what is actually happening."
How ADHD and autism compound each other
When both conditions are present, they interact in ways that make the combined picture more complex than either alone would suggest. Executive function is an area where the combination is particularly significant: both conditions independently affect executive function, but through different mechanisms, and their combined effect is not simply additive. People with both conditions often describe executive function difficulties that feel qualitatively different from what either diagnosis alone would predict.
The masking burden is also substantially higher when both conditions are present. Autistic masking, the process of suppressing autistic traits to appear neurotypical, and ADHD masking are both resource-intensive processes that, when occurring simultaneously, produce a level of exhaustion that can be difficult to account for from either diagnosis alone. People with both conditions who have masked extensively often describe a pervasive, fundamental exhaustion that feels different from burnout associated with either condition individually.
The emotional picture also has a specific quality. Rejection sensitive dysphoria is common in ADHD; autistic people also frequently experience intense emotional responses to perceived rejection and exclusion. When both conditions are present, the combined emotional sensitivity can produce a presentation that is sometimes mistaken for a personality disorder or bipolar spectrum condition.
Why one condition masks the other
Both conditions can obscure the other during assessment. In people whose autism is more prominent, clinicians may attribute ADHD symptoms to autism and therefore not consider them separately. The inattention and disorganisation characteristic of ADHD may be understood as features of autistic executive function difficulty rather than as evidence of co-occurring ADHD, producing a diagnosis that is technically correct as far as it goes but clinically incomplete.
Conversely, in people whose ADHD presentation is more prominent, autistic features may be overlooked. The impulsivity and social difficulties of ADHD can account for much of what is visible in a clinical assessment, particularly in adults who have developed compensatory strategies for their autistic traits. The autistic features remain present but are less observable in the assessment context than the ADHD ones.
Gender also plays a role here. The masking of autistic traits is particularly sophisticated in women, and both conditions in women tend to be identified later and less reliably than in men. A woman who has masked both ADHD and autism extensively may present in assessment in ways that suggest neither clearly, even though both are significantly affecting her daily life.
Considering an ADHD assessment?
A Distinct assessment addresses ADHD specifically. Our clinicians will flag where an autism assessment may also be warranted.
Assessment when both may be present
A Distinct assessment focuses specifically on ADHD, using the DSM-5 criteria and the DIVA-5 structured interview. It is not an autism assessment, and it does not produce an autism diagnosis. Where the assessing clinician identifies features that suggest autism may also be present, they will note this in the report and recommend an appropriate next step, which typically means referral for a separate autism assessment either through the NHS or through a specialist private service.
For people who already have an autism diagnosis and are seeking an ADHD assessment, the process is the same as for anyone else. Having an existing autism diagnosis does not prevent an ADHD diagnosis being made, and the DSM-5 explicitly allows both. The clinician will take the autism history into account when interpreting the ADHD assessment findings, particularly in areas where the two conditions produce overlapping features.
For people who suspect both conditions but have been diagnosed with neither, the practical question is which to pursue first. ADHD assessment is typically more accessible and faster than autism assessment in the UK private sector. Starting with ADHD is reasonable if ADHD symptoms are prominent, with the understanding that an autism assessment may follow. A consultant psychiatrist can advise on the appropriate sequence based on the clinical picture.
What it means in practice to have both
For people with both conditions, having both identified and named is typically more useful than having only one. Each diagnosis provides a framework for understanding a specific part of the experience, and neither alone gives a complete account. The support strategies, environmental adjustments, and therapeutic approaches that are most effective for ADHD are not identical to those for autism, and knowing which aspects of the experience belong to which condition allows for a more targeted and effective response.
Medication decisions are also affected. ADHD medication can be effective and appropriate in people who have both conditions, but the prescribing clinician needs to be aware of both when making that decision. Some autistic people respond differently to stimulant medication than people with ADHD alone, and the conversation about medication should reflect the full picture rather than treating the ADHD in isolation from the autism.
The community dimension is also worth noting. People with both conditions, sometimes described colloquially as AuDHD, often find that communities specifically oriented around both conditions speak more accurately to their experience than communities focused on either alone. Connecting with others who share the specific combination, rather than either condition's community separately, tends to produce a stronger sense of recognition.
This article has been reviewed for clinical accuracy by Distinct's clinical governance team, led by a consultant psychiatrist and senior NHS clinical leader with over two decades of specialist experience.