People with ADHD have 58% higher odds of IBS and nearly double the odds of constipation, analysis of 1.9 million people finds

Sarah Blake started the project as a medical student at Warwick Medical School, screening records that eventually numbered 9,613 before she and two coauthors settled on 23 studies worth pooling together. That pooled analysis, covering 1.9 million people across the United States, Sweden, Germany and South Korea, found that people with attention-deficit hyperactivity disorder had 58% higher odds of irritable bowel syndrome and nearly double the odds of constipation than people without the diagnosis. Blake, Hugo Cannon and Saran Shantikumar published the review in the Journal of Attention Disorders, examining participants ranging from age 2 to 65.

Nine Thousand Records Down to Twenty-Three Studies

A systematic review of this size starts as a filtering problem before it becomes a statistics problem. Blake and her coauthors first had to decide which of thousands of loosely related papers actually measured both an ADHD diagnosis and a gastrointestinal outcome in the same population, discarding studies that mentioned one condition only in passing or measured symptoms too inconsistently to pool.

The team searched MEDLINE, Embase and APA PsycInfo through May 2026 following PRISMA guidelines, the standard framework for conducting a systematic review, before narrowing an initial 9,613 records to the 23 that met their inclusion criteria, a winnowing process described in the original research summary of the findings. The analysis then ran random-effects meta-analyses on both individual gastrointestinal symptoms and a combined measure covering every symptom investigated, using the Joanna Briggs Institute’s quality-assessment tools to weigh how much confidence to place in each underlying study, a methodology laid out in full on the published analysis itself.

Constipation, IBS, and a Symptom Four Times More Likely

Constipation carried the highest common odds ratio of any single symptom the team examined at 1.97, close enough to double that Blake’s team described it that way in public comments. Irritable bowel syndrome followed at an odds ratio of 1.58, the 58% figure in the analysis, and the broadest measure, a composite of every gastrointestinal symptom studied, came in at 1.48. Encopresis, the medical term for loss of bowel control past the age when it is typically expected, stood apart from the rest at more than four times the odds, a gap wide enough that the authors flagged it separately rather than folding it into the general pattern.

Almost every gut symptom the team examined, from constipation to indigestion, turned out to be linked to ADHD, Blake said in comments distributed by Warwick Medical School, adding that “these symptoms can have a real impact on daily life” but risk being overlooked when clinical attention stays fixed on ADHD itself. That last point is the practical stake of the review: a child or adult managing an ADHD diagnosis may have a digestive complaint treated as incidental rather than connected, simply because clinicians are not routinely trained to look for the pairing.

A Gut-Brain Axis Still Not Understood

Shantikumar, an associate clinical professor at Warwick Medical School and the review’s senior author, was explicit about what the meta-analysis could and could not establish, cautioning in a statement carried by EurekAlert that the review cannot yet show ADHD causes the gut problems, or say exactly what is driving the link, though he called the pattern “striking enough to warrant attention.” The paper’s own framing points to alterations in the gut-brain axis, the communication network linking digestive function to neurological and psychiatric activity, as a plausible underlying mechanism, while acknowledging that mechanism remains unclear.

Untangling cause from correlation is especially hard in this data because ADHD medications themselves can affect appetite and bowel habits, and the studies pooled into the review spanned decades during which prescribing patterns for the condition changed considerably. A reviewer cannot fully separate a drug’s side effects from an underlying biological link using observational studies alone, which is why Shantikumar’s caution about mechanism sits alongside, rather than undercuts, the size of the odds ratios themselves.

A Common Diagnosis Getting a Second Look

ADHD is common enough in the United States alone that the pattern, if it holds up under further study, would touch a large population. The Centers for Disease Control and Prevention estimates that 7 million U.S. children ages 3 to 17, about 11.7%, currently have an ADHD diagnosis, and the review’s age range of 2 to 65 suggests the association is not confined to childhood. Blake’s team drew that age span from the underlying studies rather than designing it deliberately, since a meta-analysis can only pool the populations its source studies happened to examine.

What happens next is, by the authors’ own account, an open question. Neither Blake nor Shantikumar has proposed a screening protocol for gastrointestinal symptoms in ADHD patients, and the review stops at documenting the association rather than testing an intervention. Whether pediatricians and primary care physicians start asking about bowel habits during ADHD follow-up visits, the way they might ask about sleep or appetite, remains to be seen.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.

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