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Probiotics Are More Effective than Placebo in Treating the Symptoms of Irritable Bowel Syndrome (IBS)


  • In patients with IBS, are probiotics effective in reducing symptoms when compared to placebo?

Clinical Bottom Lines

  1. IBS is a functional disorder of the GI tract of unknown etiology with symptoms that include abdominal pain, bowel habit disturbance, bloating and/or flatulence.
  2. IBS affects 10 - 20% of the American population and represents a significant cause of morbidity, medical expense and loss of productivity.
  3. Probiotics are defined by the WHO as live microbial feed supplements which may beneficially affect the host by improving its microbial balance.
  4. Probiotics are a safe and effective treatment for IBS (number needed to treat = 2), based on results from a double blind, randomized control trial.1

Summary of Key Evidence

  1. In a double blind, randomized control trial, 40 individuals were divided into two groups and received either a preparation of Lactobacillus plantarum 299V or a placebo that looked and smelled the same for 4 weeks.1
  2. All patients in the study met Manning criteria for IBS, had failed other therapies for their symptoms, had been referred to a gastroenterologist and had active symptoms at the time of enrollment. Anatomic causes for their symptoms were ruled out using abdominal ultrasound and rectosigmoidoscopy or colonoscopy. There were no statistically significant differences between the two groups.
  3. Symptoms were assessed weekly by the patients using a special scoring system and physical exams at the beginning and end of the study.
  4. The primary outcome evaluated was pain relief. Secondary outcomes included overall symptoms, constipation and flatulence.
  5. 20/20 patients with IBS treated with Lactobacillus plantarum 299V had resolution of pain symptoms compared to 11/20 in the placebo group (NNT=2), 6/10 had normalization of stool frequency (compared to 2/11 in placebo group) and 10/18 patients had resolution of flatulence (compared to 5/15 patients in the control group).
  6. There were no adverse events were recorded by participants.

Additional Comments

  • Though the results of the study are encouraging, larger randomized controlled studies should be performed to evaluate the use of probiotics in this patient population.
  • The effects of probiotics are species specific and should be prescribed accordingly.
  • As with many food supplements, there is no regulation of the quality or safety of probiotic products that are on the market and patients should be made aware of this fact.
  • Probiotics are an inexpensive therapeutic option and are widely available for approximately $10.00 for a bottle of 30 capsules.


  1. Niedzielin K, Kordecki H, Birkenfeld B. A controlled, double-blind, randomized study on the efficacy of Lactobacillus plantarum 299V in patients with irritable bowel syndrome. Eur J Gastroenterol Hepatol 2001;13:1143-7.
  2. Sullivan A, Nord CE. Probiotics and gastrointestinal diseases. J Intern Med 2005;257:78-92.
  3. Thompson WG. Probiotics for irritable bowel syndrome: a light in the darkness? Eur J Gastroenterol Hepatol 2001;13:1135-6.

CAT Author: Kimberly Babb, MD

CAT Appraisers: Robert Schumacher, MD

Date appraised: March 9, 2005

Last updated November 28, 2005
Department of Pediatrics and Communicable Diseases
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