A sweeping new analysis suggests that people with attention-deficit/hyperactivity disorder (ADHD) face a substantially higher burden of functional gut problems, from irritable bowel syndrome to constipation and abdominal pain. The findings, published by researchers at Warwick Medical School, add to a growing body of evidence linking neurodevelopmental conditions with digestive health.
The systematic review, which screened more than 9,000 records and included 23 studies with over 1.9 million participants, found that ADHD was associated with increased odds of every gastrointestinal symptom examined. Overall, the odds of experiencing any such symptom were 48% higher among people with ADHD compared to those without.
“Almost every gut symptom we looked at … appeared to be associated with ADHD,” said Sarah Blake, a medical student at Warwick Medical School and co-lead author of the study. “These symptoms can have a real impact on daily life, but they could easily be overlooked if the focus is on ADHD itself.”
Strongest links: constipation and encopresis
The association was particularly pronounced for constipation, where the odds were almost twice as high, and for encopresis—the loss of bowel control—where they were more than four times as high. These findings held across different age groups and geographic regions, including studies from across Europe, North America, and Asia.
While the review does not prove that ADHD directly causes these gut problems, the consistency of the pattern is striking. The researchers point to several plausible explanations, ranging from behaviour to biology.
Why the link?
One possibility is that ADHD-related behaviours—such as emotional dysregulation, heightened stress sensitivity, irregular eating patterns, and binge eating—can disrupt gut function. Food-related sensory sensitivities, common in ADHD, may lead to selective diets low in fibre, which can affect bowel habits.
Another factor could be interoception, the ability to perceive internal bodily signals. Reduced awareness of the need to defecate might contribute to constipation or encopresis, the authors suggest.
Medication may also play a role. Stimulants like methylphenidate are known to cause side effects including appetite suppression, abdominal pain, nausea, and constipation. Sleep disturbances, which affect many people with ADHD, can further influence gastrointestinal motility and sensitivity.
The gut-brain axis
The researchers also highlight the gut microbiome as a potential biological pathway. Previous studies have found differences in the gut microbial composition of adults with ADHD compared to neurotypical controls, and other research has linked such changes to gastrointestinal symptoms.
One hypothesis is that these microbial differences could influence inflammation and the communication between the gut and the brain. Genetic factors may also contribute, though the exact mechanisms remain unclear.
“We can’t yet say ADHD causes these gut problems, or exactly what is driving the link, but the pattern is striking enough to warrant attention,” said Saran Shantikumar, associate clinical professor at Warwick Medical School. “Clinicians caring for people with ADHD may want to consider asking about gastrointestinal symptoms, particularly if they may be affecting quality of life.”
The findings echo a broader trend in European health research, where the interplay between mental health and physical conditions is gaining attention. For instance, teen social jet lag has been linked to higher anxiety, and neighbourhood deprivation to faster brain ageing—both highlighting how lifestyle and environment shape health outcomes.
For the millions of Europeans living with ADHD, the study underscores the importance of a holistic approach to care. As the authors note, gastrointestinal symptoms can be a hidden burden, and addressing them could significantly improve daily functioning and well-being.
