Irritable Bowel Syndrome

What is Irritable Bowel Syndrome?

Irritable bowel syndrome (IBS) is a medical condition characterized by chronic abdominal discomfort, constipation, bloating, and diarrhea.  By definition, IBS cannot be explained by another gastrointestinal disorder.  Symptoms of constipation and diarrhea may alternate or individuals may experience a predominance of only one symptom (eg, diarrhea-predominant IBS versus constipation-predominant IBS).

Symptoms or signs of blood in the stool, weight loss, or anemia are not characteristic and suggest a more life-threatening underlying condition.  Pain that is progressive or predominates at night is also uncharacteristic and warrants further investigation.

What Causes Irritable Bowel Syndrome?

The exact cause of IBS is unclear.  Studies have found various associations with the disease such as movement abnormalities in the gastrointestinal tract - including increased frequency of intestinal contraction.  There are theories that sensory nerves in the gut are hypersensitive in patients with irritable bowel syndrome.

Microscopic evaluation of the intestinal mucosal tissues have shown activation of certain immune cells suggesting an immunologic contribution to the disease.  Genetic factors also likely play a role as demonstrated in twin and family studies.  Psychosocial factors are also likely to contribute to irritable bowel syndrome.

How Common is Irritable Bowel Syndrome?

Irritable bowel syndrome is the most frequently diagnosed gastrointestinal disease.  Atypical or advanced cases often require referral to a gastroenterology specialist, particularly if first-line and conservative measures are unsuccessful.

The prevalence of irritable bowel syndrome is about 10%-15% in North America.  Similarly, in Europe, its prevalence is almost 12%.  The condition affects both genders, young patients, and the elderly.  Women are twice as likely to have the disease compared to men.

Signs and Symptoms

Irritable bowel syndrome can produce a variety of gastrointestinal symptoms and signs, which typically include:

  • Abdominal pain
  • Abdominal discomfort and cramping
  • Bloating
  • Constipation
  • Diarrhea

Patients may have a predominance of diarrhea or constipation – occasionally diarrhea and constipation alternate.  A classic feature is abdominal pain that is significantly relieved with defecation.

Symptoms and signs that suggest a serious underlying disease other than IBS include:

  • Weight loss & anorexia
  • Blood in the stool – melena or hematochezia
  • Anemia
  • Nighttime symptoms
  • Progressive symptoms


The diagnosis of irritable bowel syndrome is suggested based on symptoms and physical examination.  Diagnostic criteria typically include recurrent abdominal pain ≥3 days per month in the last 3 months.  These additional features are also usually present:

  • Symptom improvement with defecation
  • Symptom onset related to a change in stool frequency
  • Symptom onset associated with a change in stool appearance

Laboratory and imaging studies are generally performed to rule out underlying life-threatening medical disorders.  This is usually performed in patients with alarm features such as blood in the stool, anorexia, or iron deficiency anemia.  It may also be considered in patients that have a close family history of colon cancer or inflammatory bowel disease.

Commonly ordered blood tests include a CMP (comprehensive metabolic panel), CBC (complete blood cell count), and thyroid function studies (TSH, free T4).  Stool studies are frequently obtained to evaluate for evidence of inflammation or infections organisms.  Your doctor may recommend an ultrasound or CT scan of the abdomen to rule out other conditions.

Patients are frequently referred to gastroenterologist for upper endoscopy and colonoscopy.  During upper endoscopy, your doctor will visualize the esophagus, stomach, and small intestines by advancing a camera down your gastrointestinal tract through the mouth.  Colonoscopy is performed similarly, but the camera is advanced up the rectum.  Patients are usually sedated with medications during these procedures for comfort.

Irritable Bowel Syndrome Medication and Treatment

Irritable bowel syndrome is treated with lifestyle changes and medications.  Lifestyle changes frequently include dietary modification such as the exclusion of fermentable sugars, lactose, and gluten.  Patients with constipation may also benefit from a trial of Psyllium, a fiber supplement that acts as a bulk laxative – promoting bowel movements.

Pharmacologic therapy may be necessary for patients that have persistent symptoms despite the aforementioned measures.  Treatment is based on the gastrointestinal symptoms that predominate.  MiraLax (polyethylene glycol 3350) is an osmotic laxative that is often useful for constipation.  Patients that are unresponsive may benefit from Amitiza (lubiprostone) or Linzess (linaclotide).

Patients with abdominal pain may respond well to as needed antispasmodic agents such as Bentyl (dicyclomine).  Those with abdominal pain and coexisting depression may respond to tricyclic antidepressants such as Elavil (amitriptyline).

Antidiarrheal medications such as Imodium (loperamide) are useful in individuals with diarrhea-predominant symptoms.  Xifaxan (rifaximin) is generally reserved for patients with severe symptoms that have failed other therapies.


  1. Ford AC, Moayyedi P, Lacy BE, et al. American College of Gastroenterology monograph on the management of irritable bowel syndrome and chronic idiopathic constipation. Am J Gastroenterol 2014; 109 Suppl 1:S2. -
  2. American College of Gastroenterology Task Force on Irritable Bowel Syndrome, Brandt LJ, Chey WD, et al. An evidence-based position statement on the management of irritable bowel syndrome. Am J Gastroenterol 2009; 104 Suppl 1:S1. -

Irritable Bowel Syndrome Medication

The above information is an educational aid only. It is not intended as medical advice for individual conditions or treatments. Talk to your doctor, nurse or pharmacist before following any medical regimen to see if it is safe and effective for you.