Complex Link Exists Between ADHD and IBS, Gastric Reflux, Ulcers: New Research

July 22, 2025

ADHD and post-traumatic stress disorder (PTSD) may cause several common gastrointestinal diseases, and individuals with ADHD are 63% more likely to develop irritable bowel syndrome (IBS) than their neurotypical peers, according to new genetic research¹ and a meta-analysis.² Together, these two studies shed light on the multi-layered relationship between ADHD and common gastrointestinal disorders such as reflux, gastritis, and IBS, offering support for the growing awareness of gut health’s influence on ADHD symptoms.

The first study, published in Medicine, sought to determine whether a causal relationship exists between gastrointestinal diseases and ADHD as well as PTSD. Researchers performed a Mendelian randomization analysis using data from the FinnGen study related to 24 gastrointestinal diseases, and data from the Psychiatric Genomics Consortium related to ADHD and PTSD.

Researchers found that genetic susceptibility to ADHD was linked to:

• gastroesophageal reflux
• gastric ulcer
• duodenal ulcer
• chronic gastritis

Genetic susceptibility to PTSD was linked to:

• pancreatic cancer

This data, concluded the study authors, “provides evidence supporting causal relationship between PTSD and ADHD with specific gastrointestinal diseases.”

ADHD and IBS: High Correlation Revealed Worldwide

A second study, published in Scientific Reports, investigated the association between ADHD and intestinal disorders. The large-scale meta-analysis analyzed 11 studies conducted on 3.8 million people from four continents, including more than 175,000 with an ADHD diagnosis. Researchers explored associations with nine intestinal disorders, including irritable bowel disease (IBD), IBS, celiac disease, peptic ulcers, and recurrent abdominal pain.

Individuals with ADHD were found to be 63% more likely to have IBS than their neurotypical peers. The overall risk estimates between ADHD and all types of GI disorders were found to be just slightly elevated until researchers excluded one outlier study with a small sample size and outpatient control (vs community control); after that, the overall association between ADHD and all GI disorders rose to statistical significance, with an odds ratio of 1.47.

These findings highlight the influential role of gut health on ADHD. “An altered gut microbiome and its inflammatory effect is the potential link that bridges the gap between ADHD and intestinal disorder,” wrote the study’s authors. “The dynamic bidirectional communication between the gut microbiota and the central nervous system influences brain function, cognition, and behavior.”

ADHD and GI issues: a Multi-System Inflammatory Explanation

This bidirectional link was explored in a recent ADDitude webinar titled “The Surprising Association Between ADHD & Inflammation,” with James Kustow, BMedSci, BMBS, MRCPsych. “Problems with the digestive system frequently occur in people with ADHD, impeding gut motility and nutrition, and causing chronic pain and discomfort,” Kustow explained.

He went on to reveal that several multi-system syndromes common in people with ADHD — including mast cell activation syndrome (MCAS), dysautonomia, and hypermobility syndromes — likely play a role in intestinal disorders.

“The autonomic nervous system is responsible for the peristaltic movement through the gut, so dysautonomia causes sluggish gut,” Kustow explained. “Mast cells in the gut that get activated cause swelling, which limits flow. The combination of poor peristaltic movement and inflammation causes the contents of the gut to stagnate, leading to gastrointestinal problems.”

Ultimately, Kustow and the researchers of the two new studies hope that further research into the connections between gut health, gastrointestinal disorders, and ADHD will equip patients with new tools with which to better manage both chronic conditions.

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