A review of 23 studies involving more than 1.9 million people found that those with ADHD had 48% higher odds of gastrointestinal symptoms, including constipation, diarrhoea and abdominal pain.
A new systematic review and meta-analysis suggests that attention-deficit hyperactivity disorder is linked to a markedly higher burden of digestive problems, adding to evidence that the gut and the brain may be more closely connected than many clinicians once assumed. According to the paper published in the Journal of Attention Disorders, researchers pooled findings from 23 studies covering more than 1.9 million people and found that those with ADHD were more likely to report a broad range of gastrointestinal symptoms, including constipation, diarrhoea, abdominal pain, indigestion and irritable bowel syndrome.
The review drew on studies published through May 2026 and included children and adults from a wide range of countries, among them the United States, Sweden, Israel, Germany, China, South Korea, Spain, Greece, Turkey, Iran and India. The authors focused on symptoms rather than confirmed structural gastrointestinal disease, which matters because they were trying to identify whether digestive complaints are more common even when another diagnosed bowel disorder is not the obvious explanation.
Across the combined data, people with ADHD had about 48% higher odds of gastrointestinal symptoms overall, according to the meta-analysis. Some individual problems stood out even more sharply: constipation was nearly twice as likely, diarrhoea was more than twice as likely, and abdominal pain and indigestion were also significantly more common. Encopresis, or involuntary soiling, showed one of the strongest links, with odds more than four times higher in people with ADHD than in those without the condition.
The researchers said there are several possible explanations, though none has been proven. Behavioural factors may play a part if ADHD makes it harder to keep regular mealtimes, maintain a balanced diet or respond promptly to bodily cues. Sensory sensitivities could also narrow food choices and reduce fibre intake. The paper also points to medication effects, since stimulant drugs can cause stomach upset and appetite changes, although the authors note that some of the strongest associations, such as constipation and soiling, are not classic stimulant side effects.
The study does not show that ADHD causes digestive disease, and it does not imply that every stomach complaint in someone with ADHD has the same origin. Still, the findings may matter for people with coeliac disease, because symptoms such as bloating, abdominal pain, constipation and diarrhoea can overlap with gluten exposure, irritable bowel syndrome and other functional gut disorders. For parents, caregivers and patients, the practical message is that ongoing digestive symptoms deserve careful review rather than automatic assumptions about one cause, especially when a gluten-free diet is already being followed.
Disclaimer: This content is for informational purposes only and is not intended to be a substitute for professional medical judgment, advice, diagnosis, or treatment.
