irritable bowel syndrome (IBS), condition characterized by constipation, diarrhea, or alternating constipation and diarrhea in the absence of any disease process. It is usually accompanied by abdominal pain, especially in the lower left quadrant, bloating, and flatulence. Other symptoms, such as heartburn, lower back pain, and agitation, may be present concurrently. The cause of irritable bowel syndrome is unknown. There is no test for the disorder, though tests may be done to rule out other conditions that have similar symptoms; on examination there are no physical abnormalities. The symptoms result from a disturbance of the normal peristaltic movements of the lower intestine. IBS is the most common gastrointestinal complaint in the United States. It affects twice as many women as it does men. In some individuals it is made worse by emotional stress, spicy foods, or excessive caffeine consumption. Symptoms can be minimized by a high-fiber diet and other dietary changes and antispasmodic drugs. Acupuncture is helpful in many cases.