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ADHD and stomach problems: what new research shows

Stomach ache, bloating, constipation or diarrhoea: many people with ADHD recognise this, as do many parents of children with ADHD. A large new study confirms that these complaints are clearly more common in ADHD.

What does the study show?

Researchers pooled 23 studies with more than 1.9 million participants in total, all with a formal ADHD diagnosis (Blake et al., Journal of Attention Disorders, 2026). These were functional complaints: the gut works less well, without tests finding an underlying disease.

Every complaint studied was more common in ADHD:

  • digestive complaints overall: about one and a half times more common;
  • irritable bowel syndrome (IBS): about 1.6 times more common;
  • constipation: almost twice as common;
  • involuntary soiling in children (encopresis): more than four times as common.

Possible explanations

The researchers point to three possible factors, which may also combine: different communication between the brain and the gut (the gut-brain axis), differences in gut bacteria, and a side effect of ADHD medication such as methylphenidate, which can cause stomach ache or reduced appetite. Why the link exists is not yet established.

What does this mean for you?

If digestive complaints keep coming back for you or your child, mention it to the treating doctor, especially if they started around the same time as medication. Seek care sooner for blood in the stool, unintended weight loss, fever, night-time symptoms or persistent diarrhoea: these signs always call for further investigation, ADHD or not.

Read also: free app to track your ADHD medication.

Source: Blake S, Cannon H, Shantikumar S. The Association Between Attention-Deficit Hyperactivity Disorder and Gastrointestinal Symptoms: A Systematic Review and Meta-Analysis. Journal of Attention Disorders, 2026. doi.org/10.1177/10870547261469626. The figures are odds ratios; for common complaints they make the difference look slightly larger than it really is.