University of Warwick researchers have analyzed data from over 1.9 million people across 23 studies and found that ADHD is linked to an almost 50% increase in overall gastrointestinal symptoms compared with people without ADHD The association was even stronger for specific problems: nearly double the odds of constipation, a 58% increase in irritable bowel syndrome, and more than four times the odds of encopresis (loss of bowel control).