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Being Autistic and having ADHD?

By Dr Michelle Garnett & Prof Tony Attwood

During a diagnostic assessment for autism with an adult it is quite common for the adult to also query whether they have attention deficit hyperactivity disorder (ADHD). So, what does a diagnostic assessment for ADHD entail? And can it be subsumed within a diagnostic assessment for autism?

Diagnosis of Autism

Best practice guidelines for diagnostic assessment of autism include spending time with the person seeking the diagnostic assessment, at least one hour, but sometimes up to 3 hours. It is important to also gain psychometric data, usually from questionnaires, but sometimes from assessments of particular skills, for example the ability to read non-verbal communication, or to read emotion in the eyes. Collection of collateral information, that is information from people other than the person being diagnosed, for example a partner, a family member or a friend, is necessary. This information can be gathered either during the diagnostic interview, through self-report questionnaires, or a telephone or Internet appointment later.

Assessing for ADHD

It is entirely possible to assess for ADHD at the same time as assessing for autism and is indeed advisable. For both conditions it is very important to gain information about the developmental history of the person, from their earliest memories through to the end of high school. When interviewing for an assessment of autism there is a great emphasis on the social aspects of the person’s childhood and adolescence, when assessing for ADHD there also needs to be a strong emphasis on the academic aspects of their schooling experience. Particular questions about the person’s capacity for focus, attention, organising their belongings and time, how well the person could plan and prioritise academic learning, and reference to these concerns by teachers in school reports are very helpful.

Being Autistic and having ADHD

Research has shown over several decades now that having a comorbid diagnosis of ADHD with autism is very common and occurs in the majority (60%) of autistic children and adolescents (Stevens, Peng and Barnard-Brak 2016). A more recent meta-analysis showed the range across 63 studies to be between 40 and 70% (Rong et al, 2021). Even if the person does not meet full diagnostic criteria for ADHD, they often show fragments of the condition. We also find that it is common for an autistic adult with ADHD to navigate high school and university successfully, but once their life becomes more complicated, for example with a partner, a mortgage and a family, they start having significant difficulties managing and completing the varied and multiple demands on their time and attention. Without understanding that they have ADHD, the person can begin to question their own self efficacy, and even their own self-worth, as they feel that they are failing life tasks that “everyone else” seems to be navigating.  We have seen many adults present to our clinic for depression, only to discover that the driving force of the depression is untreated ADHD.

Our recommendations for diagnosticians:

As a diagnostician commencing a diagnostic assessment for autism, it is our recommendation that you both screen for ADHD and be prepared to fully assess ADHD during the diagnostic assessment, or to refer for more testing if that is deemed to be needed.

They are a number of excellent screeners for adult ADHD. We use the Adult ADHD Self-Report Scale (ASRS) from Novopsych. The scale has good internal consistency, and concurrent validity. It has high sensitivity and moderate positive predictive power, suggesting it would rarely miss ADHD in an adult who had ADHD. It has only moderate specificity indicating it that it is quite successful at not identifying someone with ADHD when they do not have the disorder. The norms are based on a large population. Based on percentiles, it is easy to determine whether the individual is likely to have ADHD.

As in any diagnostic assessment, it is important to assess not only for inclusiveness and exclusiveness to the diagnostic assessment criteria, but also determine intervention and a plan for support.  Sometimes it can become apparent that there is an underlying learning disability, and more intensive psychometric assessment is warranted.

Typically, an ADHD diagnosis requires understanding and observation of the person’s functioning across multiple settings, for example home, leisure, school and or work. Multiple informants make the diagnostic assessment more accurate and reliable. 

Whether to include neuropsychological assessment for a diagnostic assessment for ADHD is reliant on clinical judgement. Our general consideration is, if more detailed information is required to ascertain funding for support, or detailed supports for university and/or work, it is more likely that we will refer for neuropsychological assessment. This assessment typically involves assessment of auditory short-term memory, working memory, attention, concentration, and planning tasks. 

Once a diagnosis is made, it is important to speak with the client about their options for treatment. There is considerable research suggesting that a combination of medication, dietary and lifestyle changes, and use of particular strategies to minimise the effects of ADHD on daily life, can be very helpful. If a positive diagnosis of ADHD is made, refer to a psychiatrist who is skilled in this area for consideration of the use of medication.

Where to next?

If you are interested in finding out more about diagnostic assessment for an individual who may have autism and/or any other comorbid conditions including ADHD, consider our online course, Diagnosis for Autistic Adults.

If you are a professional involved in providing therapy and support for autistic adults, you will find our course, Support & Therapy for Autistic Adults helpful.


Stevens, Peng and Barnard-Brak (2016) Research in Autism Spectrum Disorders 31, 11-18.

Rong, Y., Chang-Yiang, Y., Yang, Y., Jin, Y., & Wang Y. (2021). Prevalence of attention-deficit/hyperactivity disorder in individuals with autism spectrum disorder: A meta-analysis. Research in Autism Spectrum Disorders, 83.