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Neurodivergence in Adulthood: The Case of the Undiagnosed

The misunderstood relationship between ADHD and autism in adults.

Key points

  • ADHD and autism spectrum disorder are two commonly-known neurodevelopmental disorders.
  • A lot of adults are beginning to notice symptoms of one or both of the disorders.
  • These disorders have their own key distinctions, but research is seeing a lot of overlap.
 Greg Rakozy/Unsplash
ADHD and autism are two well-known neurodevelopmental disorders.
Source: Greg Rakozy/Unsplash

Attention deficit hyperactivity disorder (ADHD) and autism spectrum disorder (ASD, or autism) are two commonly heard neurodevelopmental disorders.

This means that they are a result of the way that the brain develops, and impact the way that an individual processes information, makes decisions, interacts with others, and much more.

However, just because ADHD and ASD are two common household names, does not mean that they are well understood.

Decades of stigma and misinformation have left many confused on what it means to be neurodivergent. Neurodivergence, in comparison to being neurotypical, is an umbrella term for anyone whose brain is built and/or functions differently than what is considered average—or typical.

ADHD and autism fall squarely beneath this umbrella, but very few people understand the complexities of neurodivergent brains. This can lead to some individuals coming to very surprising realizations about friends, family, and most notably, themselves.

These days, disorders like ADHD and autism have gained a lot of media attention, particularly on social media apps like TikTok, as more and more people have shared their experiences with ASD, ADHD, or both. Much of this attention has come from people realizing that ADHD and autism share an interesting and unique relationship with one another.

While much of this relationship is still being explored, one thing that is becoming abundantly clear is that having ADHD, ASD, might not look like many people think it does, especially in adulthood.

Dev Asangbam
The affect of ADHD and autism on adults can cause daily impairment
Source: Dev Asangbam

What’s What?

On paper, ADHD and ASD are easy to identify and differentiate.

ADHD can be characterized by several core factors. The most well-known include difficulty controlling or maintaining attention, hyperactivity, impulsivity, forgetfulness, and challenges with processing information.

There are also plenty of lesser-known symptoms of ADHD, though, that significantly impact people daily; things like emotional dysregulation, low motivation, impaired social skills, hyper-focus, and even time blindness are constant obstacles for individuals with ADHD.

Meanwhile, ASD is usually defined by challenges interpreting social cues or others’ body language, trouble regulating emotions, repetitive physical behaviors, strict adherence to routine, and hyper-fixation on special interests.

Where things get difficult is when we realize that these disorders are not black and white. As stated in the name autism spectrum disorder, neurodivergence exists on a vast and multi-dimensional spectrum.

This means that symptoms of both can vary depending on factors like genetics, gender, environment, and in the case of so many undiagnosed individuals, age.

Since ADHD and autism symptoms typically first appear at a young age, it’s no wonder our attention goes right to how symptoms show up in kids.

So, even though they each have their own clearly distinguishable symptoms, getting the proper diagnosis and treatment is far from easy—and as people get older, it certainly does not get any easier.

Now pan over to a young adult scrolling through social media where they see a tweet, or a TikTok, and the symptoms the creator is describing are starting to sound very familiar...

But wait, I can’t have that … can I?

Nadine Shaabana via Unsplash
ADHD and ASD have several core differences - but can still be hard to tell apart
Source: Nadine Shaabana via Unsplash

Can you?

Hearing that you might have ADHD or autism, let alone both, as an adult can be confusing—if not pretty jarring. With all the misinformation and stigma that accompanies neurodivergence, it’s no surprise that someone would do a double-take at the idea.

And yet, around 4.4% of the U.S.’s adult population is estimated to have ADHD, and roughly 2.2% with ASD—and that’s just for those who have been diagnosed.

An added layer of difficulty for adults with suspected ADHD and/or autism is that researchers are beginning to see a striking amount of comorbidity—or co-occurring diagnoses—between the two.

In fact, recent studies show that roughly 20-30% of children that meet criteria for ADHD also meet criteria for ASD, while 50-80% of children with autism meet criteria for ADHD.

However, until recently many doctors would avoid diagnosing someone with both disorders. This is because even though so many individuals with one disorder displayed symptoms of the other, the 4th edition of the Diagnostic and Statistics Manual (DSM – IV) made it so that the two could never be diagnosed together.

What does this mean for people living with one or both of these disorders? For some, it meant that they were diagnosed with whichever one was most prominent at the time, leaving the other to be left out entirely.

For others, it meant being diagnosed incorrectly—while they remain very distinct disorders, many of their symptoms look alike in practice.

I mean, if a person is already diagnosed with autism, then hyper-focus must just be hyper-fixation on a special interest, or trouble interacting with others must be a result of missed social cues, right? That is, until the untreated motivation, memory, or problem-solving issues lead someone to struggle day in and day out.

Not to mention the plethora of stigma and misinformation about these disorders. Media portrayals of autistic children screaming in a restaurant, or of a young boy running around a classroom, frequently cause parents to fear the possibility of these disorders presenting in their children.

 Johnathan Borba/Unsplash
With ADHD and autism being diagnosed so often in children, adults have a hard time recognizing symptoms.
Source: Johnathan Borba/Unsplash

For these reasons, among others, it is no surprise that so many people go well into adulthood before being diagnosed with ADHD, ASD, or both.

This is especially true for people who identify as and/or are socialized as girls, who are more likely to present with less outwardly expressive symptoms, or to mask their symptoms overall.

All these factors—misinformation, cultural factors, stigma, unclear diagnostic criteria, similar symptom presentation, among many others—leave thousands of adults worldwide to suffer unnecessarily in school, work, home, you name it.

Seeking help as an adult neurodivergent person, or any neurodivergent person, can be tricky. However, the more awareness that we bring to the realities of these disorders, the better prepared we can be to provide support for those who truly need it.

So, maybe you’ve started to suspect that your symptoms might be affecting you more than you originally thought. Or maybe you saw a TikTok video that hit a little too close to home. Either way, it can be easy to assume it’s all in your head—but that’s because it is. And so the question instead becomes: What’s so wrong with that?


Centers for Disease Control and Prevention. (2020). Key Findings: CDC Releases First Estimates of the Number of Adults Living with Autism Spectrum Disorder in the United States. U.S. Department of Health and Human Services.….

National Institute of Mental Health. (2017). Attention-Deficit Hyperactivity Disorders (ADHD). U.S. Department of Health and Human Services.…)%20versus%20females%20(3.2%25).

Leitner, Y. (2014). The co-occurrence of autism and attention deficit hyperactivity disorder in children–what do we know?. Frontiers in Human Neuroscience, 8, 268.

Morris-Rosendahl, D. J., & Crocq, M. A. (2020). Neurodevelopmental disorders—the history and future of a diagnostic concept. Dialogues in Clinical Neuroscience, 22(1), 65.

Gershon, J., & Gershon, J. (2002). A meta-analytic review of gender differences in ADHD. Journal of Attention Disorders, 5(3), 143-154.

Centers for Disease Control and Prevention. (2020). Symptoms and Diagnosis of ADHD. U.S. Department of Health and Human Services.

Centers for Disease Control and Prevention. (2020). Symptoms and Diagnosis of ADHD. U.S. Department of Health and Human Services.

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