Irritable bowel syndrome is a common functional disorder of the gastrointestinal tract manifested by persistent and agonizing symptoms. Irritable bowel syndrome is not inherited as the causes of irritable bowel syndrome are not fully understood. As its name implies, patients with the syndrome have a more sensitive intestine that causes the symptoms. If the intestine is overactive, the result is rapid diarrhea. On the contrary, a "lazy" intestine leads to constipation.