What you need to know about ADHD and gut health
- The gut and brain communicate constantly via the gut-brain axis and vagus nerve — and for many people with ADHD, the gut is a significant piece of the puzzle.
- The gut microbiome produces around 90% of the body’s serotonin, as well as dopamine precursors and calming neurotransmitters like GABA.
- Compromised gut lining (leaky gut) can trigger neuroinflammation that directly impacts focus, mood, and behaviour.
- Microba gut microbiome testing can show us exactly what’s happening rather than guessing — and help build targeted, effective support.
Why the gut keeps coming up in ADHD
If you or your child has ADHD, chances are most of the focus so far has been on the brain. Medications, strategies, routines, sensory tools. And all of that absolutely has its place. But there’s another system worth paying serious attention to, and it lives a lot further south.
The gut.
Over the last decade, research into ADHD gut health has grown enormously. What’s emerging is genuinely fascinating: the gut communicates constantly with the brain, produces a significant portion of the body’s neurotransmitters, and houses an immune system that can either support or undermine how we think, focus and feel. When the gut is struggling, the brain often is too.
In clinic, I see this pattern regularly. Kids and adults with ADHD who also deal with constipation, bloating, food sensitivities, or a history of frequent antibiotic use. It’s rarely a coincidence.
Gut health isn’t separate from brain health in ADHD — they’re part of the same conversation.
The gut-brain axis: a two-way conversation
The gut-brain axis is a sophisticated communication network linking the digestive system and the central nervous system. It works through the vagus nerve, the enteric nervous system (the gut’s own independent nerve network), immune signalling, and hormonal pathways.
The vagus nerve is the superhighway of this system. Here’s what surprises most people: roughly 80 to 90 percent of the signals travelling along it go from the gut up to the brain, not the other way around. The gut is quite literally briefing the brain all day long.
For people with ADHD, vagal tone — how efficiently the vagus nerve functions — is an area of growing research interest. Poor vagal tone has been associated with difficulty regulating the nervous system, increased impulsivity, emotional dysregulation, and reduced attentional control.
The enteric nervous system adds another layer. This network of over 500 million neurons lining the gut wall operates largely independently of the brain. When its environment is disrupted, the signals it sends upstream change accordingly.
The microbiome and ADHD: what your gut bacteria are doing
The gut microbiome — the trillions of bacteria and other microorganisms living in the digestive tract — has an outsized influence on brain function. Here’s how:
Serotonin production
Around 90–95% of the body’s serotonin is made in the gut. Serotonin influences mood, sleep, impulse regulation, and is a precursor to melatonin. When the microbiome isn’t producing adequate serotonin, all of those areas are affected.
Dopamine precursors
Dopamine is the neurotransmitter most directly implicated in ADHD. While dopamine itself doesn’t cross the blood-brain barrier, gut bacteria influence the availability of the precursors that do — including L-DOPA.
GABA
GABA is the brain’s primary calming neurotransmitter, playing a key role in reducing anxiety and supporting focus. Certain gut bacteria are involved in its production — and these species are consistently lower in people with ADHD.
Short-chain fatty acids
SCFAs like butyrate are produced when gut bacteria ferment dietary fibre. Butyrate feeds the gut lining, supports blood-brain barrier integrity, and has anti-inflammatory effects in the central nervous system. Altered SCFA profiles are consistently found in children with ADHD.
What the research says
Studies consistently find distinct microbiome profiles in people with ADHD — lower Bifidobacterium, lower Lactobacillus, and lower Faecalibacterium. A 2025 meta-analysis also found a 63% increased risk of IBS in people with ADHD, covering data from over 175,000 individuals.
Leaky gut, neuroinflammation, and ADHD
The gut lining is designed to be selectively permeable — allowing nutrients through while keeping bacteria, toxins, and larger molecules out. When that lining becomes compromised (leaky gut), things get through that shouldn’t.
This triggers an immune response. Inflammatory signalling compounds called cytokines increase in circulation, and inflammation begins to affect the brain as well as the gut. This state of neuroinflammation is increasingly understood as a meaningful contributing factor in ADHD symptoms.
The current model gaining traction in research: gut dysbiosis leads to increased intestinal permeability → systemic inflammation → impaired blood-brain barrier function → neurological environment associated with worsening of symptoms associated with ADHD. It’s not the whole picture, but it’s a significant part of it.
Signs that gut health may be contributing to ADHD symptoms: frequent digestive complaints, history of repeated antibiotic use, significant food sensitivities, strong sugar or processed food cravings, sleep difficulties, mood instability or anxiety alongside ADHD, and history of formula feeding or caesarean birth.
Microbiome testing: actually seeing what’s going on
One of the most valuable things we can do when ADHD and gut symptoms overlap is to look at what’s actually happening in the microbiome — rather than applying a generic protocol and hoping for the best.
This is where I find gut microbiome testing genuinely useful. I currently use Microba, a gut testing service that uses deep shotgun metagenomic sequencing — a significantly more detailed method than standard testing. Rather than just identifying which bacterial families are present, it can identify bacteria at the species and strain level, measure functional capacity, and assess markers like SCFA-producing potential and inflammation-related species and metabolites.
What Microba testing can show
- Microbiome diversity and composition
- SCFA-producing bacteria and estimated butyrate production capacity
- Presence of inflammatory or dysbiotic species
- Markers of intestinal permeability risk
- Markers associated with poor motility, inflammation, altered immune response, and there are some markers associated with an increased likelihood of mood issues
Testing is done at home with a stool sample and returned to the lab via post — straightforward for both adults and kids. The results are detailed but translated into accessible language, which I find really useful for explaining findings to patients.
This information takes the guesswork out of gut support. Rather than applying a one-size-fits-all approach, we can see exactly where the gaps are and tailor support accordingly — specific probiotic strains, prebiotic foods, dietary shifts, and targeted herbal or nutritional support where indicated.
It currently costs ~$400-$500 depending on which level of test you choose which is not feasible for some people, but certainly gut health work can still be done without this, just not with the same level of fine tuning.
Common questions about ADHD and gut health
Naturopathic support for ADHD gut health isn’t about replacing other management strategies — it works alongside them. The focus is on identifying the specific factors influencing your (or your child’s) presentation, and building support from there.
References
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- Ng, R. W., Chen, Z., Yang, L., et al. (2025). Association between attention-deficit/hyperactivity disorders and intestinal disorders: A systematic review and meta-analysis. Scientific Reports, 15, 19278. https://doi.org/10.1038/s41598-025-04303-x
- Steckler, R., Magzal, F., Kokot, M., Walkowiak, J., & Tamir, S. (2024). Disrupted gut harmony in attention-deficit/hyperactivity disorder: Dysbiosis and decreased short-chain fatty acids. Brain, Behavior, and Immunity – Health, 40, 100829. https://doi.org/10.1016/j.bbih.2024.100829
- Stiernborg, M., Debelius, J. W., Yang, L. L., Skott, E., Millischer, V., Giacobini, M., et al. (2023). Bacterial gut microbiome differences in adults with ADHD and in children with ADHD on psychostimulant medication. Brain, Behavior, and Immunity, 110, 310–321. https://doi.org/10.1016/j.bbi.2023.03.012
- Phasouk, K., Saengnipanthkul, S., Lao-araya, M., & Chattipakorn, N. (2025). Impact of psychostimulants on microbiota and short-chain fatty acids alterations in children with attention-deficit/hyperactivity disorder. Scientific Reports, 15. https://doi.org/10.1038/s41598-025-87546-y
- Jiang, H., Zhang, X., Yu, Z., Zhang, Z., Deng, M., Zhao, J., & Ge, X. (2021). Gut microbiota signature in treatment-naïve attention-deficit/hyperactivity disorder. Frontiers in Cell and Developmental Biology, 9, 329. https://pmc.ncbi.nlm.nih.gov/articles/PMC12309550/
- Liu, Y., Li, W., Zhong, X., et al. (2025). Symptom-specific gut microbial and metabolic profiles in ADHD reveal SCFA deficiency as a key pathogenic mechanism. ISME Journal. https://pmc.ncbi.nlm.nih.gov/articles/PMC12309550/
Ready to look at the bigger picture?
If you or your child is navigating ADHD and you’ve noticed gut symptoms, food sensitivities, sleep struggles or mood instability alongside the attention challenges, it’s worth exploring the gut connection. I offer gut-focused naturopathic consultations for both adults and children, including Microba testing where indicated.
