What’s the difference between ADHD and autism?

Research keeps finding more similarities.

“How do you know if you’re ADHD or autistic?”

I get questions like this in my DM’s a lot. They are also questions I am trying to not worry about so much anymore, because I think the premise of these questions is flawed.

They are based on the assumption that these are concrete, biological conditions with a rigid set of symptoms that can be accurately differentiated, but they’re not.

Diagnosis is still completely based on observable behavior, which makes it more of a narrative process than a biological one. You don’t get diagnosed with a brain scan or a blood test — it depends what you tell the doctor about yourself or your child, and what they see in the stories you share. It also depends heavily on their implicit biases regarding race, gender, and class.

Colloquially, I’ve come to see these words — ADHD, autistic — as rhetorical, narrative tools, short-hand for a common human experience.

Like telling someone you’re “such a Gemini”, referring to yourself as ADHD calls up a list of traits and a reference for a certain experience. You don’t have to explain it all because you have this one word carrying a loaded pack of meaning for you.

This is convenient! And it allows us to relate more efficiently, to talk about our personalities and our lives in less words, and to find community. But it’s also vague, stereotypical, and generalizing, which is perhaps a double-edged sword for neurotypes that contain such massive variability (what science-types call “heterogeneous”).

My ADHD is likely not your ADHD. The category contains so many different kinds of people, even doctors have admitted that “the diagnosis is a mess” — in his book ADHD Nation, Alan Schwarz details a massive public hearing held by the National Institute of Health that made headlines in 1998.

After three days of presentations in hopes of reaching an official consensus on what ADHD is, a journalist asked a panel of doctors to describe the typical person with ADHD, and they couldn’t. Because there isn’t one!

I sometimes wonder if I was misdiagnosed as ADHD, when really I am just autistic. When I hear people talk about how hard it is to read a book with ADHD, I can’t relate. I hyperfocus on reading, and can spend hours glued to a book. This is something I realized differentiates me from a large part of the ADHD community, and a reason I’ve begun to actively work on synthesizing the readings I share into more bite-sized, digestible formats.

There are many “ADHD things” I do relate to, though, like working memory problems, struggling to organize and prioritize, experiencing time differently (read: always being late), hyperfocus, daydreaming, distractibility, wild tangents. But many of these things are common experiences for autistic people, too.

Research Says: More Similarities than Differences

We still have not found any definitive biomarkers of ADHD in the brain, meaning, you can’t scan a brain and point to a certain structure and say, there it is, that’s the ADHD!

Some studies have found differences in gray matter and size of certain brain structures, but these are generally very slight percentages, around 3%, and some did not account for age and weight-related differences, or the fact that their participants had been medicated from a young age, so it’s hard to say if these brain size differences are truly because of an innate biological difference called ADHD or not.

It’s true we have found many genes associated with ADHD and autism, but we’re talking like, hundreds of genes, many of them also associated with other conditions like bipolar and schizophrenia and depression. A 2019 study found that both ADHD and autism show mutations in the MAP1A gene, increasing the likelihood of having one or the other by 15 times.

While this is intriguing research, we still don’t have anything genetically conclusive, because both ADHD and autism are highly heritable conditions that involve a ton of different genes.

In short, it’s complicated! But a growing body of research is finding “more similarities than differences” between the two.

A 2004 study that looked at 100 autistic children “found 95% had attention problems, 75% had motor difficulties, 86% had problems with regulation of activity level, and 50% had impulsiveness.”

Another found “children with ADHD had elevated levels of impairment in all three autistic symptom domains, namely social deficits, communication and stereotyped behaviors.”

This 2020 paper found “children with ASD had elevated ADHD symptoms, and vice versa, suggesting that symptoms are not specific to diagnostic categories.”

Another 2020 paper took fMRI imaging of autistic and ADHD brains and put them into a computer to see if an algorithm could classify ADHD or autism scans as compared to neurotypical ones, and if they could distinguish ADHD and autism from each other.

The computer did the first task pretty well, but struggled with the second, suggesting that “functional brain connectivity is either too similar between both groups, or too variable within each group for reliable classificationusing the method they employed.

“ADHD and ASD share deficits in executive functions (EF), such as planning, decision making, inhibition, and working memory,” noted this 2014 study, which looked at imaging of ADHD, autistic, and ADHD+autistic brains while doing a temporal discounting task (which is basically a measure of how well you can tolerate delayed gratification, and is used to measure impulsivity).

Their findings actually suggested that people with both ADHD and autism could be in a category all their own that is “characterised by a different underlying neurofunctional pathology than the two pure disorders.” So, it’s maybe not a combo of the two things, but it’s own thing! (This study, it must be noted, had several conflicts of interest involving pharmaceutical companies, who very much have a vested interest in creating new diagnostic categories to be treated with their drugs.)

Drugs as Diagnostics?

My partner and I have had long talks about our respective comorbidities. They have an ADHD diagnosis, too, but we recently discovered they tick all the boxes for dyslexia, a category that also contains struggles with focus and distractibility. (It’s quite common to be diagnosed with both conditions — a study of twins found comorbidity of 40%.)

We both use stimulants sometimes to help us focus, and many people think that if a stimulant “works” for you, that is hard proof that you have ADHD. But this is not entirely correct — it’s a myth that’s been allowed to flourish because it’s good for pharmaceutical sales.

The first use of a stimulant for behavior modification happened on accident at a children’s home under the care of Dr. Charles Bradley, before the ADHD category even existed.

Many accounts of this history point out that pharmaceutical companies were actively looking for a medical application for stimulants — they had originally attempted to market them for nasal decongestion, but people liked it so much they were basically chewing on their inhalers to get high!

Schwarz details a scene in his book that illustrates how the first serious studies on potential uses for stimulants in children, by Dr. Leon Eisenberg and Dr. Keith Connors, were encouraged by a nudge-nudge-wink-wink $5000 check from a pharma rep, back when they were still calling their patients “disturbed children” with “Minimal Brain Dysfunction”.

The ADHD category was developed alongside the pharmaceuticals used to treat it, and we can’t ignore this history and its effects on the pop science narratives we are sold about these drugs, namely, that they only work if you have ADHD.

“Stimulant drugs do improve the ability (even without ADHD) to focus and pay attention,” says this 2012 review of their effects.

“Stimulants improve sustained, focused attention…[Stimulants] do not improve (and may even impair) short-term acquisition of information. In addition, [stimulants] do not improve, and may impair ‘cognitive flexibility’.”

Cognitive flexibility includes creative problem-solving and divergent thinking, some of the things I love most about my brain, and a huge reason I hate taking stimulants. They make me irritable and I feel like they stunt my ability to spiral into tangents, which is how some of my best creative work happens.

I will take Adderall to help me concentrate on boring admin tasks but end up just getting glued to something completely unrelated for 3 hours straight. If I take more than 5 mg, I become a personality-devoid zombie (another well-documented effect of these drugs, especially at higher doses).

My partner, in contrast, takes 3x as much as I do and doesn’t feel nearly as many negative side effects. They do, however, say they have to plan to be looking at the “right” thing when their meds kick in, lest they risk getting aggressively stuck on something unrelated.

This effect has also been documented in studies of children who take stimulants — they get stuck on a task and are unable to stop doing it, to the point that it deters their learning in school and their ability to socialize with their peers.

But still, lots of doctors are under the impression that if Adderall helps you focus, then you have ADHD, but this is a frustrating, circular sort of reasoning. Why did the Adderall work? Because you have ADHD. How do you know you have ADHD? Because the Adderall worked. Not the most solid of logic there, but a very profitable argument if you’re trying to sell pharmaceuticals.

Taking a Label Maker to a Galaxy

When we consider that ADHD people experience sensory sensitivity and social communication issues, and autistic and dyslexic people struggle with attention, and how often all of these are considered co-morbid, the Venn diagrams here can start to look like big prismatic circles.

So does it really matter which traits belong to ADHD and which belong to autism or dyslexia? Can we really ever know? Sometimes it feels like we’re trying to take a label maker to a galaxy, desperately scrambling to fit a million stars and black holes into neat little boxes we can stack on the shelf of our identity.

Except that galaxy is our brains — infinitely complex, with as many neurons as the Milky Way has burning suns. (Sorry, I’m being poetic — the actual estimate as of 2009 is 86 billion.)

That is a massive amount of complexity to fit into one or two vague, oversimplified categories! It feels a bit laughable when you think about it this way; we are such silly, complicated hominids, trying desperately to assemble some manner of order in a universe that tends toward entropy.

I am getting more comfortable swimming in this undefinable sea of complexity, coming to terms with the fact that the words we have for ourselves and our experiences are small, insubstantial and do very little justice to who we really are.

writer + digital artist focused on disability, queerness, and culture | they/them

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