Irritable Bowel Syndrome (IBS) – Diagnosis, Symptoms, and Treatment

Doctor Nathan LeDeaux, MD

Medically reviewed by Dr. Nathan LeDeaux, MD

Medical Professional

Updated - January 11, 2021

Nathan LeDeaux is an emergency medicine physician at the University of Wisconsin and got his M.D. from Northwestern University in Chicago Illinois.

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What is Irritable Bowel Syndrome?

Irritable bowel syndrome (IBS) is a medical condition characterized by chronic abdominal discomfort, constipation, bloating, and diarrhea.  While these symptoms are commonly seen in many disorders, a diagnosis of IBS requires that no other diagnosable condition be present.  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 such as blood in the stool, weight loss, or anemia are not typical of IBS. These symptoms suggest a more life-threatening underlying condition.  Pain that is progressive or more common at night is also atypical and warrants further investigation.

What Causes Irritable Bowel Syndrome?

IBS has no known cause, it has been associated with changes in intestinal motility, the pattern of contraction that leads to food moving through the intestines. This is thought to be due to changes in the nervous system of the intestines. If this is a cause or result of IBS is uncertain and research is ongoing. 

Microscopic evaluation of the intestinal walls have shown activation of certain immune cells which suggests that the immune system may also play a role in the development or progression of 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. Individuals with a history of anxiety and depression are more likely to have more severe presentations of IBS. 

How Common is Irritable Bowel Syndrome?

Irritable bowel syndrome is the most frequently diagnosed gastrointestinal disease. 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 IBS compared to men.

Since IBS is a diagnosis of exclusion, some cases of IBS may actually be other illnesses that are misdiagnosed or have not yet been discovered. This is thought to be uncommon but the true risk of misdiagnosis always exists. 

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 of IBS is abdominal pain, bloating, and cramping 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 symptoms that only appear at night or are worse at night. 
  • Progressive symptoms symptoms that worsen significantly over time without short periods of improvement. 


The diagnosis of IBS is one of exclusion, this means that numerous other conditions must be ruled out for a diagnosis of IBS. After other gastrointestinal conditions are ruled out, specific diagnostic criteria typically include recurrent abdominal pain ≥3 days per month in the last 3 months. Other common symptoms that suggest a diagnosis of IBS include:

  • 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 viruses, parasites, and abnormal bacteria. A CT scan or ultrasound of the abdomen may be ordered to rule out structural problems with the intestines such as bowel obstruction, cancer, and congenital abnormalities. 

Patients are frequently referred to gastroenterologists 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 both lifestyle changes and medications.  Lifestyle changes generally 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 regular 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 an antispasmodic agent such as Bentyl (dicyclomine), which is taken as needed during episodes of acute pain.  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 an antibiotic that can reduce inflammation and immune system overactivity in the intestines. It 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.