Patients with attention-deficit/hyperactivity disorder had higher odds of gastrointestinal symptoms compared with neurotypical controls, with particularly strong associations for encopresis and constipation.
Researchers conducted a systematic review and meta-analysis according to PRISMA 2020 guidelines and prospectively registered the protocol with PROSPERO. MEDLINE, Embase, and APA PsycInfo were searched from inception through May 12, 2026. Among 9,613 records identified, 23 observational studies representing more than 1.9 million participants met inclusion criteria. The studies included 16 cross-sectional studies, 6 retrospective cohort studies, and 1 case-control study, with participants ranging in age from 2 years through adulthood.
The researchers evaluated total gastrointestinal (GI) symptoms among patients with attention-deficit/hyperactivity disorder (ADHD) compared with neurotypical controls. Individual outcomes included constipation, encopresis, irritable bowel syndrome (IBS), dyspepsia, diarrhea, abdominal pain, unspecified stomach or bowel problems, and flatulence. Studies of formally diagnosed organic GI diseases were excluded, and only studies with a control group contributed to the meta-analysis.
Across 6 studies included in the pooled analysis of total GI symptoms, patients with ADHD had 1.48 times the odds of symptoms compared with neurotypical controls. A seventh study that could not be included in the pooled analysis because it measured GI symptom severity rather than prevalence similarly reported higher symptom scores among patients with ADHD.
The largest association emerged for encopresis. Across 5 studies, patients with ADHD had 4.32 times the odds of encopresis compared with controls. In 6 studies evaluating constipation, patients with ADHD had 1.97 times the odds. Both analyses showed substantial between-study heterogeneity.
Higher odds were also observed across other GI outcomes. ADHD was associated with 2.18 times the odds of diarrhea, 1.88 times the odds of abdominal pain, 1.82 times the odds of unspecified stomach or bowel problems, 1.58 times the odds of IBS, and 1.52 times the odds of dyspepsia. The findings for IBS, dyspepsia, and unspecified stomach or bowel problems showed little or no between-study heterogeneity, whereas heterogeneity was substantial for diarrhea and abdominal pain. Flatulence could not be pooled because the 2 studies evaluating it used different outcome measures.
The researchers described several potential explanations for the associations, including emotional dysregulation and stress, irregular eating patterns, sensory food sensitivities, altered interoception, sleep disturbance, medication effects, and differences in the gut microbiome. However, these mechanisms were not tested by the meta-analysis. Stimulant medications, including methylphenidate, can produce GI adverse effects such as abdominal pain, nausea, and constipation, complicating interpretation of the observed associations.
The analysis had several limitations. Only English-language studies were included, publication bias could not be assessed, and substantial heterogeneity for several outcomes could not be fully explained. The researchers also did not perform sensitivity analyses or contact study investigators for missing numerical data. Most studies did not stratify results by medication status, limiting the researchers’ ability to distinguish GI symptoms potentially associated with ADHD from those related to treatment.
For clinical practice, the researchers recommended actively asking patients with ADHD about GI symptoms and considering multidisciplinary management involving gastroenterology or dietetics for complex cases. The findings support an association between ADHD and a range of GI symptoms but do not establish causality. The researchers called for longitudinal studies to determine whether GI symptoms precede ADHD or develop as a consequence of the condition or its treatment and to better distinguish intrinsic biological pathways from medication effects.
“While our review highlights a robust association between ADHD and GI symptoms, it cannot confirm causality,” wrote lead study author Sarah Blake, of Warwick Medical School, and colleagues.
The authors reported no funding or conflicts of interest.
Source: Journal of Attention Disorders