What the heck is ADHD?

Why scientists can’t seem to agree on one explanation.

Thank you for the overwhelming response to the first article in this series. Hundreds of likes, reshares, and thoughtful conversations. There’s great discussion in the comments, so feel free to connect with others there.

You’ve probably heard someone say, “Everyone has ADHD these days.”

In the U.S., diagnoses more than doubled since the early 1990s. I know it’s tempting to dismiss this as overdiagnosis or a cultural fad, but the reality is more complex.

First, let’s get a couple of things out of the way. We know what ADHD isn’t. It’s not a product of too much sugar, bad parenting, or laziness. It involves real differences in brain function and development.

But do we know what it actually is? Ask most researchers, and they’ll give you something like this:

“a polygenic neurodevelopmental condition that affects attention, impulse control, and regulation of activity and emotion”

It’s a neat definition, but underneath lies a patchwork of competing theories that looks like complete mayhem. In the course of my own research, I’ve identified 19 distinct models of ADHD described in the scientific literature!¹

So why is ADHD so hard to pin down with one theory?

How ADHD works (and why it’s complicated)

In the 1990s, researchers thought they had cracked the code. Russell Barkley’s theory proposed an elegant hierarchical model: a single core deficit in behavioral inhibition could explain the cascade of problems seen in ADHD by disrupting executive functions like working memory and self-regulation.

But then, the plot thickened. New findings showed that not all people with ADHD had inhibition problems. Some also struggled with delay, motivation, emotion, or timing.

If you think of the brain like a busy airport with planes (thoughts, actions, emotions) that need to take off and land on schedule, scientists have identified several domains where the air traffic control can go awry in ADHD, leading to delays, sudden takeoffs, or forgotten landings:

• Executive function: Planning, working memory, automatic responses.

• Reward and motivation: Preference for immediate over delayed rewards.

• Arousal and alertness: Trouble maintaining steady effort or focus.

• Timing and regulation: Difficulty with time perception and transitions.

• Emotion and mood: Intense emotions and difficulty regulating them.

That’s why you’ve probably noticed some people can’t sit still while others are daydreaming. Some speak non-stop; others barely talk at all. They can be impulsive or overwhelmed by emotion. And some don’t seem obviously different until their environment changes.

This variability is part of why ADHD is so hard to pin down.² Despite decades of research, there’s no blood test. No scan that confirms it. Diagnosis is currently based on patterns of behavior that disrupt daily life and persist across settings, but not everybody agrees as to what those patterns of behavior actually look like.

As a result, the field began to fracture into specialized theories. You can roughly place these theories of ADHD into four buckets :

1. Executive dysfunction. One of the earliest and most enduring views. ADHD involves difficulty managing internal control systems like planning, remembering what to do next, or stopping an automatic response. This explains impulsivity and disorganization, but not motivation issues or mood swings.

2. Delay aversion. This view proposes that some symptoms of ADHD arise not just from difficulties with cognitive control, but from how people react emotionally to waiting. Delays don’t just feel boring but can be unbearable. This can lead to choices that prioritize immediate relief, like quitting a task early or avoiding anything that involves waiting.

3. Default mode interference. The brain has a default mode network that becomes active when we’re not focused on the outside world. In ADHD, this system seems to stay active even during tasks, creating interference – like background noise interrupting a conversation. This might help explain those mid-sentence lapses or zoning out during simple tasks.

4. Dopamine models. ADHD has been linked to how the brain handles dopamine, a chemical involved in reward and motivation. In many people with ADHD, the brain appears less able to anticipate rewards or maintain interest over time. This can make long-term goals feel flat and distant.

And to complicate things further, theories of ADHD operate at different levels of explanation:

• Genetic: ADHD has a strong inherited component. No single gene causes it, but many genes each with small effects seem to contribute to it.

• Neurobiological: Brain networks involved in attention, timing, and reward seem to behave differently in ADHD, sometimes more variable, less connected, or slower to mature.

• Cognitive-behavioral: ADHD traits affect how people think, learn, respond to feedback, and regulate effort.

• Environmental: Stress, trauma, classroom and work demands, sleep, and parenting style might all interact with ADHD traits.

• Evolutionary: ADHD traits such as hyperfocus, hypervigilance and hypercuriosity might have once been adaptive in nomadic, high-stimulus environments, and might have become mismatched to modern life.

Today, most researchers agree that ADHD isn’t explained by any single mechanism. Instead, we see integrative frameworks that suggest ADHD arises from multiple interacting systems, shaped by genetics, brain development, and environment.

So... is ADHD a thing? Yes and no.

Rethinking what ADHD is

ADHD is real in the sense that it describes a consistent pattern of difficulties that cause genuine problems for millions of people. But it’s not a single thing with a single cause.

Rather than a fixed medical condition you either have or don’t, ADHD might be better understood as an umbrella term for a spectrum of traits³ that appear together more often than by chance, and that seem to share common roots in brain development, genetics, and our environment.

This helps explain a puzzle: ADHD diagnoses have increased sharply over the past 30 years. That’s partly due to better recognition and reduced stigma, but it also reflects how the category has stretched to capture a broader range of behaviors and struggles.

That also helps explain why different treatments help different people, why individuals with ADHD can look so different from one another, and why the condition has been so hard to pin down with a single theory.

At a practical level, this suggests that cookie-cutter approaches whether in treatment, education, or support are likely to miss the mark. Some people might benefit most from medication, others from environmental changes, and still others from strategies that work with their natural curiosity rather than against it.

It means parents and teachers might need different approaches for different kids, and that self-advocacy becomes about understanding your own particular constellation of traits instead of trying to figure out how you fit into a predetermined “ADHD box.”

The good news is that new research directions are moving beyond the binary diagnostic category toward more nuanced approaches. Emerging research includes:

• Brain networks. Tracking how large-scale brain systems interact in real time to reveal the moment-to-moment patterns behind ADHD symptoms.

• Genetic profiling. Mapping how combinations of small genetic risks shape brain development differently in different people.

• Individualized treatments. Matching interventions to each person’s profile of strengths and challenges instead of applying standard protocols.

• Environmental factors: Recognizing environments as part of the solution, including how we structure schools, workplaces, and daily life.

Some scientists, myself included, are also exploring how traits like novelty-seeking and curiosity – which are linked to dopamine function – might tie together the cognitive, motivational, and emotional sides of ADHD, and how people with ADHD can better harness their unique strengths.

In the future, what we now call “ADHD” might be broken down into more biologically distinct subtypes or reframed dimensionally to measure levels of impulsivity, distractibility, curiosity, and emotional regulation, rather than using a single catch-all diagnosis. That shift could help make support more personalized.

The bottom line

So yes, ADHD is a thing. But it’s likely not one thing. It’s currently a useful label for multiple, interacting processes that vary from person to person, giving clinicians a way to support patients, educators a lens to support students, and researchers a map to explore.

The explosion of theories isn’t a failure of science but a sign of a complicated, deeply human condition we’re still working to understand.

The real question isn’t whether ADHD is “real.” The question is: can we get comfortable with that complexity so people can find what actually works for them?

1. I’m working on an overview of these 19 theories, stay tuned!

2. This article was already getting long so I didn’t even touch on co-occurring conditions, but we know that ADHD often overlaps with other neurodevelopmental differences like autism and dyslexia, as well as with mental health conditions such as anxiety, depression, addictions, and sleep disorders.

3. This overview represents my own current scientific understanding, which continues to evolve. I’m a researcher, not a clinician, so if you’re concerned about ADHD symptoms, please consider consulting with a healthcare professional.