In this edition of Five Whys, we look to understand a little about the ADHD brain and why it causes us to spiral in overthinking.

I was diagnosed with ADHD recently. Late diagnosis, as an adult, after a lifetime of wondering why certain things felt so much harder than they seemed to for everyone else. Why I'd sit in a meeting and feel my thoughts scatter in six directions at once. Why I'd lie awake at night, unable to stop my brain running through the same loop over and over, normally about work-related issues. Why I would pause on writing, rewriting, pausing, then rewriting an Slack message over and over, worried about how the person might take it and generally wondering why I never quite felt like I fitted in with society, and couldn't explain why.

Like many people, my anxiety has been treated as anxiety and that's still the case. However, it's important to know that anxiety coexists alongside the ADHD. Think of it that my anxiety is the smoke, where my ADHD is the fire.

Since the diagnosis, things have started to make sense in a way they never did before. Not all at once, and not completely. But piece by piece, the picture is becoming clearer and I can maybe start talking to myself a little kinder.

This article is one piece of that picture, I am sure there are many now I can understand why my brain does what it does.

It is, as my specialist reminded me, only the tip of the iceberg.

Why #1: Why does the ADHD brain spiral?

The ADHD brain struggles to interrupt a thought once it gains momentum.

In a neurotypical brain, thoughts arise and then get filtered. Some are followed. Others are dismissed. The brain acts as a kind of editor, deciding what deserves attention and what can be let go.

In the ADHD brain, that editing process is unreliable. A thought arrives and instead of being assessed and filed, it runs. And then it keeps running, picking up speed, collecting related worries and worst case scenarios along the way, until what started as a passing concern has become a full spiral — trying to find a pattern — a solution.

It doesn't feel like a choice. That's because it isn't one.

But why does the ADHD brain struggle to interrupt a thought in the first place?

ADHD affects an estimated 2.6 million people in the UK. Despite this, the average waiting time for an NHS adult ADHD assessment is currently over two years in many areas. Many adults go undiagnosed for decades.

Why #2: Why can't the ADHD brain interrupt a thought?

Inhibitory control, the brain's ability to put the brakes on a response or a thought, is impaired in ADHD.

Think of inhibitory control as a mental handbrake. In most brains, it fires automatically. A thought starts heading somewhere unhelpful and the handbrake kicks in. The thought slows. Something else takes over.

In the ADHD brain, that handbrake is unreliable. It doesn't always fire when it should. Thoughts that should be slowed or stopped aren't. They continue unchecked, gathering intensity as they go.

This isn't a discipline problem or a focus problem. It is a neurological one. The system designed to interrupt unhelpful thoughts doesn't work the same way it does in other brains.

But impaired inhibitory control alone doesn't fully explain spiralling. Plenty of people have intrusive thoughts without spiralling. So what makes ADHD different?

Why #3: Why does impaired inhibitory control lead to spiralling rather than just distraction?

Poor working memory means the brain cannot hold onto a reassuring thought long enough to use it.

Working through a difficult emotion is not a single step. It requires holding multiple pieces of information at the same time. The worrying thought. The context around it. The counter-argument. The reassurance that things will probably be fine.

Most brains can juggle those pieces. The ADHD brain struggles to. Working memory, the mental workspace where thoughts are held and processed, is impaired. So while the anxious thought runs freely, the calming counter-thought, the "this is going to be okay", gets dropped.

The worry stays. The reassurance doesn't. And without anything to counterbalance it, the spiral deepens.

Which raises something important. Why does the emotional thought run so much harder than the rational one?

Why #4: Why does the emotional thought always win?

Emotional dysregulation is a core feature of ADHD, not a side effect of it.

The ADHD brain reacts to emotional triggers faster and more intensely than a neurotypical brain. A small worry lands harder. A passing criticism stings longer. A moment of uncertainty escalates more quickly. Not because of weakness or sensitivity, but because the emotional response fires before the rational brain has time to catch up.

Research increasingly recognises emotional dysregulation not as an occasional complication of ADHD but as one of its defining characteristics. The emotional accelerator is always slightly over-sensitive. The rational brake is always slightly slow.

Put those two things together and a small thought can become a large spiral before anything has had the chance to intervene.

But why is the rational brake so slow? What is actually happening in the brain?

Why #5: Why is the rational brake always slow?

The prefrontal cortex, the part of the brain responsible for rational thought, impulse control, and emotional regulation, is the exact part of the brain that ADHD affects most.

This is the root of it. The prefrontal cortex is supposed to act as the regulator. It assesses emotional responses, applies context, holds reassuring information in place, and signals when a thought has gone far enough. It is, in effect, the off switch.

In the ADHD brain, that system functions differently. The prefrontal cortex is slower to activate, less consistent in its regulation, and less able to override the emotional response firing beneath it. The part of the brain that should stop the spiral is the same part of the brain that ADHD impairs most directly.

The spiral isn't overthinking. It isn't anxiety, though the two often travel together. It is a neurological loop with a structurally weakened off switch. The brain is not broken. It is wired differently, in a way that makes certain loops very hard to escape.

Understanding that distinction matters more than it might seem.

In Summary

The ADHD brain spirals because the system designed to interrupt runaway thoughts, hold reassuring context in place, and regulate emotional responses, is the same system that ADHD impairs most directly.

The root cause is prefrontal cortex dysfunction. Not overthinking. Not weakness. Not a failure to just calm down. A neurological difference that makes the brain's own off switch unreliable, leaving emotional thoughts to run further and harder than they should.

For anyone who has spent years wondering why their brain won't just stop, this is the answer. The loop was never a choice. The off switch was always the problem.

And knowing that, it turns out, makes quite a lot of other things start to make sense too.

Have a great week, thank you for reading and remember to stay curious and ask lots of questions this week.

Matt