Causes: The cause of IBS is unknown. Emotional stress, diet, some drugs and hormonal factors seem to aggravate the symptoms. No anatomic cause can be found on laboratory tests, x-rays, and biopsies.

Signs and Symptoms: IBS tends to begin in adolescence and the 20s, causing bouts of symptoms that recur at irregular periods. Onset in late adult life is less common but not rare. Symptoms are often triggered by food, particularly fats, or by stress.

Patients have abdominal discomfort, which varies considerably but is often located in the lower abdomen, steady or cramping in nature, and relieved by having a bowel movement. In addition, abdominal discomfort is temporally associated with changes in stool frequency (increased in diarrhea-predominant IBS and decreased in constipation-predominant IBS) and consistency (ie, loose or lumpy and hard). Pain or discomfort related to defecation is likely to be of bowel origin; that associated with exercise, movement, urination, or menstruation usually has a different cause. Although bowel patterns are relatively consistent in most patients, it is not unusual for patients to alternate between constipation and diarrhea. Patients may also have symptoms of abnormal stool passage (straining, urgency, or feeling of incomplete evacuation), pass mucus, or complain of bloating or abdominal distention. Many patients also have symptoms of dyspepsia. Some symptoms associated with IBS include fatigue, fibromyalgia, sleep disturbances and chronic headaches.


The Rome criteria are standardized symptom-based criteria for diagnosing IBS. The Rome criteria require the presence of abdominal pain or discomfort for at least 3 days/months in the last 3 months along with ≥ 2 of the following:

  • Improvement with bowel movement
  • Onset (of each episode of discomfort) associated with a change in frequency of bowel movement
  • Change in consistency of stool