By Adrian Stone, BHSc (Nutritional Medicine), BHSc (Naturopathy), Living Holistic Health — ADHD and gut problems travel together: a September 2026 review of 23 studies and 1.9 million people found 48% higher odds of gut symptoms and nearly double the odds of constipation. This article explains what is going on and what to do about it.
Your Gut Is Not Like Las Vegas · Part 2 of 5 · Part 1: the gut microbiome and MS
In Part 1 I set out the rule for this series: your gut is not like Las Vegas. What happens there doesn’t stay there — and association is not cause. This time the condition is one I see a lot of in clinic: ADHD. In children, and in the adults who recognised themselves while their child was being assessed.
Ask a parent of a child with ADHD about tummy aches, constipation or “just not eating.” You’ll usually get a knowing look. Ask an adult with ADHD about their gut. You’ll often hear about IBS, reflux, or a bowel that has never been regular. For years that was anecdote. As of September 2026, it’s a number.
How Strongly Are ADHD and Gut Problems Linked?
A September 2026 systematic review pooled 23 studies and more than 1.9 million people. ADHD was associated with 48% higher odds of gut symptoms overall, 58% higher odds of irritable bowel syndrome, nearly double the odds of constipation, and more than four times the odds of encopresis (soiling past toilet-training age). Every symptom examined was more common in ADHD.
The review — Blake, Cannon and Shantikumar at Warwick Medical School, Journal of Attention Disorders, September 2026 — screened 9,613 records to get to those 23 studies. It only included people with a formal DSM or ICD diagnosis of ADHD. It deliberately excluded diagnosed organic gut disease such as Crohn’s or coeliac disease. What’s left is functional gut trouble: symptoms without a structural cause on the scope or the scan.
The pooled odds ratios were 1.48 (95% CI 1.35–1.62) for total gut symptoms, 1.58 for IBS and 1.97 for constipation. For encopresis, soiling in a child past the age of toilet training, it was 4.32. Lead author Sarah Blake told Euronews that almost every gut symptom they looked at appeared to be associated with ADHD.
Two things about that 48% before it turns into a headline. It’s an odds ratio, not a doubling of your risk. Odds and risk diverge as symptoms get common, and gut symptoms are common. And it’s an average across studies of different designs, ages and countries. It tells us the link is real and consistent. It doesn’t tell us why.
Does ADHD Cause Gut Problems, or Is It the Other Way Around?
Nobody knows yet, and the honest answer may be “both, plus a third thing.” The review’s authors are explicit: it does not establish that ADHD causes gut symptoms. The candidate explanations run in every direction: gut bacteria, the vagus nerve, behaviour and eating patterns, medication, sleep and shared genetics.
This is exactly the place where the single-cause story tempts everyone. “ADHD is really a gut problem” sells books. So does “it’s just the medication.” Neither survives contact with the data. Let me take the mechanisms one at a time. They are not equally supported, and they don’t lead to the same actions.
Is the Gut Microbiome Different in People with ADHD?
Yes, detectably — but not dramatically, and not consistently enough to be a test. A 2025 meta-analysis across neurodevelopmental conditions found no difference in overall diversity, only shifts in which organisms were present. One much-cited pilot linked an ADHD-associated bacterial shift to weaker brain responses to reward. It had 19 people with ADHD and 77 controls.
What the meta-analysis shows
The 2025 meta-analysis in Frontiers in Microbiology pooled studies of ADHD, autism and tic disorders. Alpha diversity — the “how many kinds” measure — didn’t differ from controls. Beta diversity did: the communities were distinguishable, with a few families and genera shifted. The authors flag heterogeneity and small samples as the limitation. Same pattern as MS in Part 1: it’s which bacteria, not how many.
The 19-person pilot
The pilot everyone quotes is Aarts and colleagues, 2017. In 19 people with ADHD and 77 controls they saw a nominal increase in Bifidobacterium. They traced it to a bacterial gene involved in making phenylalanine, a precursor of dopamine. More of this gene function went with a weaker brain response to anticipated reward on fMRI. Blunted reward anticipation is a hallmark of ADHD. It’s a beautiful, mechanistically coherent result, and I’d love it to be true. It is also a 19-person pilot that has never been cleanly replicated, and I’m not going to build a treatment on it.
The early-life signal
There’s a stronger early-life signal. A 2022 meta-analysis of ten studies and 2.4 million children found that antibiotic exposure in pregnancy was associated with a 23% higher hazard of a later ADHD diagnosis. Antibiotics in the first two years of life were not. That’s a modest effect from observational data; the mothers who needed antibiotics may differ in other ways. But it’s consistent with animal work showing that disrupting the early microbiome changes behaviour. It’s a reason to use antibiotics carefully, not a reason for guilt. Most children exposed to antibiotics in pregnancy do not develop ADHD.
Could the Medication Be Causing the Gut Symptoms?
Partly, in some people — but the link existed before the medication and exists in the unmedicated too. Stimulant medication for ADHD commonly reduces appetite and can cause abdominal pain. The Warwick authors specifically call for research that separates medication effects from the condition itself, which tells you the current data can’t fully do it.
A 2018 Cochrane review of non-randomised studies of the most common stimulant medication found that about 31% of children reported decreased appetite and about 11% reported abdominal pain. The certainty of those estimates is very low. Appetite suppression means smaller, later, more erratic meals — which is a straight road to constipation in a child.
But the review that opened this article included studies of unmedicated people and children too young for medication. The association held. So medication is a contributor to gut symptoms in some people with ADHD, not the explanation for the link. If your child’s gut changed when the medication started, raise it with the prescriber. It is a known effect and there are ways to manage it. It is not a reason to stop or change a medication on your own.
Why Would ADHD Itself Lead to Gut Problems?
Because the traits of ADHD shape how, when and what a person eats, how they read their own body, and how they sleep. Irregular meals, sensory food avoidance, low fibre, weaker awareness of the urge to go, chronic stress physiology and disturbed sleep all slow the gut. None of this needs a microbiome explanation, and all of it is modifiable.
The held signal
This is the part I find most useful clinically, because it’s where the levers are. The Warwick paper lists the behavioural pathways: emotional dysregulation and stress sensitivity, irregular eating and binge patterns, and interoception. That last one is the sense of what’s happening inside the body. A child who doesn’t register the signal to open their bowels, or who is too absorbed to act on it, holds on. Holding on makes stool harder and the signal weaker. That loop is the textbook route to chronic constipation and to encopresis. It is why the encopresis odds ratio in the review is so much higher than the rest.
The narrowed plate
Sensory sensitivity to texture and smell narrows the diet. The foods that fall off the list first are usually the fibrous ones: vegetables, legumes, whole grains, fruit with skin on. Low fibre, low fluid, irregular timing — the gut slows.
The nervous system
Then there’s the nervous system. ADHD carries a heavy load of stress physiology — what I call sympathetic dominance, one of my four root drivers. In a fight-or-flight state the body diverts blood and attention away from digestion. If the body is stressed, it cannot properly digest, any more than it can properly heal. Poor sleep, which travels with ADHD independently of medication, does the same thing to gut motility.
And the vagus nerve runs both ways. The gut sends more signal to the brain than the brain sends to the gut. A chronically irritable bowel is a chronically noisy input to a brain that already struggles to filter noise.
Does Diet Quality Matter in ADHD and Gut Problems?
Yes, and it’s the one lever that touches every mechanism. In a Spanish case-control study of 120 children, low adherence to a Mediterranean-style diet went with roughly seven times the odds of an ADHD diagnosis — wide confidence intervals, cross-sectional, so cause runs both ways. But fibre, regular meals and whole foods are exactly what a sluggish gut needs.
The Pediatrics study found that low intake of fruit, vegetables, pasta and rice was associated with ADHD diagnosis. So were skipping breakfast, fast food, high sugar and soft drink intake, and low intake of fatty fish. The odds ratio of 7.07 has wide confidence intervals (2.65–18.84) and the authors themselves say the design can’t establish causality. A child with ADHD may eat this way because of their ADHD. But that’s the point: the pattern is the same one that produces constipation, and it’s changeable.
What about probiotics? A 2025 meta-analysis pooled 15 randomised trials of gut-targeted interventions (probiotics, prebiotics, diet changes and faecal transplant) in autism and ADHD. It found a small overall benefit on symptoms, larger in ADHD (standardised mean difference −0.24) than in autism. Eight-week interventions showed the clearest effect. The authors call the evidence preliminary and the trials small. I’d call it interesting enough to keep watching and nowhere near enough to promise anything. Diet first.
What Should You Do If Your Child Has ADHD and Gut Problems?
Treat the gut symptoms as real and worth investigating, not as part of the package. Start with the basics that slow a gut: fibre, fluid, regular meals and a toilet routine. Check nutrient status, since restricted eating and appetite suppression both deplete it. And keep every step alongside the paediatrician or GP who manages the ADHD itself.
In my clinic the first appointment for a child with ADHD and gut symptoms looks like this. A timeline of when the gut trouble started relative to the ADHD symptoms and any medication. A food diary that shows the actual pattern, not the ideal one. Sleep, stress and screen habits. And a look at every blood test already done. Iron, zinc, vitamin D and B12 are the ones most often low in restricted eaters. Low iron in particular overlaps with attention and sleep; I’ve written about that in Nutrient Deficiencies in Children.
Does that child need a stool microbiome test? My rule is the same as always: only if it would better inform the plan and get a better result faster. For most children, the history and a basic blood panel tell me what I need. A gut test earns its place when symptoms persist after the basics are fixed, or when the pattern doesn’t make sense. Organic acids testing, which I’ve covered in ADHD Testing and Organic Acids, sometimes tells me more than a stool test does.
For adults with ADHD and a lifetime of IBS, the same principles apply. It’s often the first time anyone has connected the two for them.
Where Does a Naturopath Fit Alongside a Paediatrician or GP in ADHD?
Alongside, and in our own lane. We don’t diagnose or treat ADHD; that stays with your doctor, paediatrician or psychiatrist. Our part is the nutritional, herbal and lifestyle work that sits alongside their care — the gut symptoms, the restricted diet, the nutrient gaps, the sleep and the stress load that a medication review isn’t designed to cover.
Nothing in this article is a reason to change or stop a medication. If your child’s gut symptoms started or worsened with medication, tell the prescriber — that conversation belongs with them, and they have options. What we add is the work around it: a gut that moves, a diet that feeds the right bacteria, a nervous system that gets a chance to stand down. We want the body to do most of the work. We create the conditions.
I wrote more about where naturopathy fits in ADHD in Can Naturopathy Help Tackle ADHD?
What’s Next in This Series?
Part 3 goes to Parkinson’s disease, where constipation often appears years, sometimes decades, before the first tremor. The gut is now being studied as one of the places the disease may begin. It’s the most striking gut-first story in the literature, and it comes with its own set of overclaims to sort through.
Positive change means sacrifice — in this case, the sacrifice is giving up the comfort of a single explanation. Your gut is not like Las Vegas. Neither is your child’s.
If you’re in Geelong or on the Bellarine and your child’s gut has been filed under “part of the package”, the first appointment is where we start. Alongside the paediatrician or GP who manages the ADHD, never instead of them.
Your Gut Is Not Like Las Vegas — a series on why what happens in the gut doesn’t stay there.
Part 1: The gut microbiome and multiple sclerosis
Part 2: ADHD and gut problems (this article)
Part 3: Parkinson’s and constipation
Part 4: Depression, anxiety and the gut-brain axis
Part 5: Autoimmunity beyond MS
Part 1: The gut microbiome and multiple sclerosis
Part 2: ADHD and gut problems (this article)
Part 3: Parkinson’s and constipation
Part 4: Depression, anxiety and the gut-brain axis
Part 5: Autoimmunity beyond MS
Frequently Asked Questions
Are gut problems more common in people with ADHD?
Yes. A 2026 review of 23 studies and over 1.9 million people found ADHD was associated with 48% higher odds of gastrointestinal symptoms overall. IBS odds were 58% higher, constipation nearly double, and encopresis more than four times. Every gut symptom examined was more common in ADHD.
Does ADHD medication cause constipation and stomach pain?
Stimulant medication commonly reduces appetite and can cause abdominal pain, and smaller, irregular meals can lead to constipation. But the ADHD–gut link is also seen in unmedicated people and young children, so medication explains part of it, not all of it. Raise any change with the prescriber rather than adjusting medication yourself.
Can fixing the gut fix ADHD?
No evidence supports that. Small trials of gut-targeted interventions show a modest effect on ADHD symptoms that researchers describe as preliminary. Addressing gut symptoms improves comfort, eating and sleep, all of which matter. But it is support alongside standard care, not a replacement for it.
Should my child with ADHD have a gut microbiome test?
Usually not as a first step. A careful history, food diary and basic blood tests for iron, zinc, vitamin D and B12 tell a practitioner most of what they need. A stool test earns its place when symptoms persist after diet, fluid, routine and sleep have been addressed.
References
Research located via PubMed. All links go to the original papers.
- Blake S, Cannon H, Shantikumar S. The association between attention-deficit hyperactivity disorder and gastrointestinal symptoms: a systematic review and meta-analysis. J Atten Disord. 2026. https://doi.org/10.1177/10870547261469626
- Yang H, Wang A, Yang J, Luo R, Yang Y. Alterations in gut microbiota composition in neurodevelopmental disorders: a systematic review and meta-analysis. Front Microbiol. 2025;16:1650212. https://doi.org/10.3389/fmicb.2025.1650212
- Aarts E, Ederveen THA, Naaijen J, et al. Gut microbiome in ADHD and its relation to neural reward anticipation. PLoS One. 2017;12(9):e0183509. https://doi.org/10.1371/journal.pone.0183509
- Otten K, Keller L, Puiu AA, et al. Pre- and postnatal antibiotic exposure and risk of developing attention deficit hyperactivity disorder — a systematic review and meta-analysis combining evidence from human and animal studies. Neurosci Biobehav Rev. 2022;140:104776. https://doi.org/10.1016/j.neubiorev.2022.104776
- Storebø OJ, Pedersen N, Ramstad E, et al. Methylphenidate for attention deficit hyperactivity disorder (ADHD) in children and adolescents — assessment of adverse events in non-randomised studies. Cochrane Database Syst Rev. 2018;5:CD012069. https://doi.org/10.1002/14651858.CD012069.pub2
- Ríos-Hernández A, Alda JA, Farran-Codina A, Ferreira-García E, Izquierdo-Pulido M. The Mediterranean diet and ADHD in children and adolescents. Pediatrics. 2017;139(2):e20162027. https://doi.org/10.1542/peds.2016-2027
- Sun W, Ma L, Feng X, Fan Y, Cai Y, Li X. Efficacy of gut microbiota-based therapy for autism spectrum disorder and attention deficit hyperactivity disorder: a systematic review and meta-analysis. Psychol Health Med. 2025:1-25. https://doi.org/10.1080/13548506.2025.2565181
This article is general information only and is not a substitute for individual medical advice. Please speak with your GP, paediatrician or psychiatrist before starting, changing or stopping any medication or supplement. For private health consultation claiming, please enquire with your health fund to assess coverage. Nutrition consultations are covered by some private health funds — please check with yours first.
