30/09/2026
Ask a parent of a child with ADHD about tummy aches, constipation, or "just not eating", and you'll get a knowing look. Ask an adult with ADHD about their gut and you'll hear about IBS, reflux, or a bowel that has never been regular.
For years that was anecdote. This month it became a number.
A systematic review from Warwick Medical School pooled 23 studies and more than 1.9 million people, all with a formal ADHD diagnosis, and excluded diagnosed gut disease like Crohn's or coeliac. What's left is functional gut trouble. ADHD came with 48% higher odds of gut symptoms overall. 58% higher for IBS. Nearly double for constipation. More than four times for encopresis, soiling in children past toilet-training age. Every gut symptom they looked at was more common in ADHD.
Part 2 of the series, and the rule from Part 1 holds: your gut is not like Las Vegas, and association is not cause. The authors say plainly this doesn't prove ADHD causes gut problems. It might run the other way. It might be both, plus a third thing.
So what's the third thing? Probably several.
The gut bacteria are different in ADHD, but not dramatically and not consistently enough to be a test. A 2025 meta-analysis found no difference in how many kinds of bacteria, only in which ones. The famous study linking a bacterial shift to weaker reward signalling in the brain had 19 people with ADHD and 77 controls, and has never been cleanly replicated. There's a modest early-life signal too: antibiotics in pregnancy went with a 23% higher hazard of a later ADHD diagnosis across 2.4 million children. That's a reason to use antibiotics carefully, not a reason for guilt. Most children exposed do not develop ADHD.
In the research, about a third of children on stimulant medication report reduced appetite and about one in ten report stomach pain — low-certainty figures, but a known effect. Smaller, later, erratic meals are a straight road to constipation. But the gut link shows up in unmedicated people and children too young for medication, so medication is part of it, not the explanation.
And then the part I find most useful, because it's where the levers are. ADHD shapes how, when and what a person eats. Irregular meals. Sensory avoidance that drops the fibrous foods first. A weaker sense of the urge to go, so the signal is held and fades, which is the textbook route to chronic constipation and the reason the soiling figure is so much higher than the rest. Poor sleep. A nervous system stuck on: if the body is stressed, it cannot properly digest. Every one of those slows a gut. Every one of them can be worked on.
If your child has ADHD and gut problems, treat the gut as real and worth investigating, not part of the package. Fibre, fluid, regular meals, a toilet routine. Check iron, zinc, vitamin D and B12, because restricted eating depletes them. And if the gut changed when medication started, tell the prescriber. That conversation belongs with them, and they have options.
We do not diagnose ADHD and we do not treat it, but we do support you through it. Alongside your paediatrician or GP, never instead.
Full article: https://www.livingholistichealth.com.au/natural-medicine-news/adhd-and-gut-problems
Part 2 of 5. Next: Parkinson's, where constipation can show up years before the first tremor.
— Adrian Stone, Nutritionist & Naturopath, Living Holistic Health
General information only, not medical advice. Nothing here replaces care from your GP, and nothing here is a reason to start, stop or change any medication.