This article has been clinically reviewed on April 15, 2022. 

Until 2013, diagnosing both autism spectrum disorder (ASD) and attention-deficit/hyperactivity disorder (ADHD) wasn’t possible—even if a patient’s symptoms suggested comorbidity. The Diagnostic and Statistical Manual of Mental Disorders (5th ed.; DSM-5) was the first edition of the American Psychiatric Association guide to acknowledge what many clinicians had found—that a single diagnosis just didn’t capture the full range of symptoms some patients experienced.

Today, a dual diagnosis of ASD + ADHD is a valid diagnostic option. In fact, current research indicates that 30%–80% of autistic individuals have the diagnostic symptoms of ADHD, and 20%–50% of children with ADHD have the diagnostic symptoms of ASD (Kernbach et al., 2018). That overlap can make reaching the right diagnosis harder, especially when ASD and ADHD result in similar-looking behaviors.

This article takes a look at these two neurodevelopmental conditions. Understanding where they converge and where they diverge may help to clarify whether the most accurate diagnosis is ASD, ADHD, or both.

Are Autism and ADHD Related? Understanding the Complicated Interplay

ASD and ADHD are distinct conditions. Even so, there’s considerable overlap in why and how they develop. They can also affect functioning in similar ways. Here’s a glimpse of some of the territory they share.

Genetics

A stretch of DNA can sometimes contain extra copies of certain genes, known as copy number variants (CNVs). CNVs can happen on their own or they can be inherited from parents. ASD and ADHD have variants in the same regions of DNA (Thapar & Cooper, 2013). These shared CNVs don’t make ASD or ADHD inevitable, but they do raise the chances.

Researchers have also identified genes associated with both ASD and ADHD. Many of these genes are active in the production of the same neurotransmitter: dopamine (Cabana-Dominguez et al., 2022).

Pregnancy

Use of certain medications and some health conditions in the birthing parent have been linked to both ASD and ADHD. These factors may include:

• acetaminophen (Ji et al., 2019)
• valproic acid, an antiseizure medication (Wiggs et al., 2020)
• diabetes, anemia, or preeclampsia (high blood pressure; Chen et al., 2021; Wanget et al., 2021; Wiergersma et al., 2019)

Brain Structures

Brain anatomy and activity in people with neurodevelopmental conditions differ from that in people with typical development. Imaging studies have found that some brain structures, including those involved in social communication, are thinner in autistic individuals and those with ADHD (Baribeau et al., 2019). Another example: fMRI studies have shown neural connectivity differences in regions of the brain where sensorimotor activities are managed (DiMartino et al., 2013).

Early Signs of Autism and ADHD

Autism is often diagnosed by providers when parents of infants or toddlers raise concerns about expected developmental milestones. ADHD, on the other hand, can go undiagnosed until behavior issues crop up in the school years. Still, some early red flags can indicate either condition, including:

• excessive crying
• sleep problems
• eating issues
• motor delays
• difficulty interacting with others

Learn more: Early Childhood Development Stages & Beyond

Functional Impairments

ASD and ADHD present similar day-to-day challenges. Both conditions can:

• affect social interaction
• delay the development of language
• spark discomfort in new situations
• cause oppositional or defiant behavior
• interfere with attention
• limit the ability to regulate emotion
• create deficits in working memory
• result in sleep disturbances
• involve atypical sensory processing

Camouflaging and Masking

Autistic individuals, those with ADHD, and those with both often go to great lengths to disguise or compensate for their differences. They may spend time studying how neurotypical people speak, interact, and behave so they can adapt—even when it feels unfamiliar and uncomfortable. They may need to mask or camouflage to:

• escape bullying
• protect family and friends
• fit in at school or work

Masking is a costly pursuit. These compensatory strategies can cause extreme fatigue and anxiety. They can also raise the risk of suicide (Cage & Troxell-Whitman, 2019; Young et al., 2020).

Disparities in Diagnosis and Treatment

ASD and ADHD occur in all racial, ethnic, and socioeconomic groups. But a variety of barriers prevent Black, Hispanic, and lower-income families from accessing early diagnosis and treatment for ASD at the same rate as White children and families (Aylward et al., 2021). In the same way, White children are also more likely to receive ADHD diagnoses than Asian, Black, or Hispanic children. When children of different races do receive ADHD diagnoses, White children are more likely to get treatment (Shi et al., 2021).

Access to insurance and to medical or mental health care, bias among providers and educators, parental preferences, and culture all factor into these disparities.

Biological sex and gender can also influence diagnosis. The CDC reports that children assigned male at birth are around four times more likely to receive ASD diagnoses and around twice as likely to receive ADHD diagnoses. Whether these disparities stem from biological differences, social norms, or bias is a subject of ongoing debate.

Learn more: Why Are So Many Autistic Girls & Women Still Missing Out on Early Identification?

Exploring the Distinctions

The diagnostic criteria of these two conditions do not overlap. The core characteristics of ASD are differences in communication and social interaction, repeated behaviors, and specialized interests. By contrast, the core symptoms of ADHD are attention difficulties, hyperactivity, and impulsivity.

Even when symptoms appear similar, their origins often differ. Here are a few examples:

• Autistic individuals and those with ADHD often have sensory-processing differences compared to people with typical development. Autistic individuals have greater differences in auditory processing than children with ADHD or typical development. Children with ADHD score higher than those with ASD or typical development on tests that measure visual processing (Little et al., 2019).
• Autistic individuals and those with ADHD can have difficulty in making or maintaining friendships. Social communication style may be the driver in ASD, whereas impulsivity can be at the root of the problem with ADHD (Aiello et al., 2021).
• Autistic individuals and those with ADHD have a hard time paying attention to things that don’t interest them. With ASD, it may be linked to an intense focus on something else. With ADHD, that deficit is often because of distraction.
• Autistic individuals and those with ADHD often have some motor-skill impairments. Both conditions can cause problems with coordination and fine motor skills like handwriting, but repetitive movements are more common with autistic individuals and restlessness is associated with ADHD. Gray matter volumes vary in different motor-control regions of the brain, as well (Albajara Saenz et al., 2021).

What Clinicians Can Do

What does all this mean for medical professionals whose job it is to sort out the similarities and differences as they show up in individual patients? Here are a few of the practical suggestions offered by the United Kingdom ADHD Partnership:

• Use a variety of assessments, including observational and intellectual assessments, to create the clearest possible picture.
• Screen for both conditions when either condition is present.
• Consider advanced training in assessment to sharpen your skills and boost your confidence.
• Avoid “double-counting” symptoms for both ASD and ADHD.
• Look at functioning over many years if possible since symptoms can change at different ages.
• Use visual tools in addition to those that require spoken responses.
• Be aware of how culture can impact criteria such as eye contact.
• Seek information about the patient from many different sources.
• Keep an eye out for camouflaging and compensatory strategies.
• Assess the risks for each patient since some may cope in unhealthy or unproductive ways. Autistic individuals and those with ADHD have an elevated risk of self-harm and suicidal thinking.
• Work to counteract bias and other sources of disparity (Young et al., 2020).

What’s the Outlook for ASD + ADHD?

When someone has the symptoms of both ASD and ADHD, it’s often the case that ASD is diagnosed much later than when either condition presents on its own. With ASD + ADHD, the symptoms of both conditions can be more severe. Anxiety may be worse and the quality of life for patients and their families may be lower. For those reasons, an accurate, early diagnosis can be life-changing.

Further Reading on Autism

• The WPS In-Depth Guide Autism and ADHD 
• Understanding the Complicated Interplay of Autism and ADHD
• How Autism and ADHD Can Disrupt Interoception
• How to Choose the Best Autism Assessment for Your Client
• Best Practices in Autism Assessment
• Autism Conversations: Individualizing Educational Interventions with the MIGDAS-2 Evaluation Process

Videos and Webinars on Autism

• How Cyberbullying Impacts Students On and Off the Autism Spectrum
• Conversation Over Labels: A Better Way to Understand Autism
• Autism Spectrum Brains 'Get Energy' from These Things