In this article, we will review evidence for the use of probiotics in the treatment of irritable bowel syndrome (IBS) in adults. However, this does not replace the advice of your physician, whom you should always consult with for specific treatment recommendations.

The World Health Organization defines probiotics as “live microorganisms which when administered in adequate amounts confer a health benefit on the host.” They include bacteria as well as yeasts. Probiotics work in many possible ways, including:

  • lining the surface of the gastrointestinal tract and stopping harmful organisms from reaching it (competitive exclusion),
  • strengthening the tissue of the bowel wall,
  • acting as antibiotics against other bacteria, and
  • regulating the responses of the immune system, both at the level of the bowel wall and the body as a whole.

The only way to show the effectiveness of a new treatment, such as probiotics in IBS, is by doing trials in which researchers randomly choose patients to receive either probiotics or a placebo, and then compare the two groups with respect to outcomes (randomized controlled trial). We will only discuss probiotics with such studies in this article, as we cannot draw conclusions about probiotics that have not undergone this type of thorough testing.

One important factor to consider is that while there are now guidelines from Health Canada concerning the quality of probiotics sold in pharmaceutical dosage forms (e.g., tablets, capsules), there are currently no regulations concerning probiotic bacteria in food. A study done in British Columbia and reported in 2004 looked at ten different over-the-counter products labelled as containing the probiotic bacteria, Lactobacillus. Analysis showed that only five brands contained live Lactobacillus, while two of them grew no organisms whatsoever. Five brands contained other species of bacteria, not listed on the label. Of the brands that actually contained Lactobacillus, the amount that could be cultured from the product ranged from 0.8% to 1.3% of the amount stated on the product label. With the developing Health Canada guidelines for selling probiotics, this might not be an issue in the near future.

Another important point is that bacteria come in multiple strains (usually indicated by a number after the name of the bacteria, such as E. coli Nissle 1917). The results of a clinical study done with a particular strain of a bacterium might not apply to a different strain of the same species of bacteria.



In multiple clinical trials, researchers have assessed the safety of probiotics. The risks are minimal in outpatients with a normal immune system. About 30 cases of infection of the bloodstream by fungus have been reported: nearly all cases were with Saccharomyces boulardii in hospitalised patients with intravenous catheters. It was felt that the infections were the result of nurses giving probiotic pills to patients and then touching their intravenous catheters with contaminated hands.

A single case report describes a liver abscess due to Lactobacillus rhamnosus in a 74-year-old woman with diabetes (a disease associated with an increased risk of infection), who was taking the organism as a probiotic. In another case report, a 67-year-old man with an abnormal heart valve taking Lactobacillus rhamnosus developed infection of the heart (endocarditis) a few days after the removal of decayed teeth, which we know to be a risk factor for such infections. Thus, there are small but potential risks of infections from probiotics in outpatients who have specific risk factors, such as diabetes, poor dentition, or those who are on drugs that can suppress the immune system (e.g., steroids, azathioprine, infliximab, adalimumab).


Results of Recent Studies (See Table 1)

  • Three studies have looked at Lactobacillus plantarum 299V (Tuzen®) in IBS, involving a total of 112 patients. Not all of the studies looked at each symptom, and the results were as follows: overall symptoms improved for patients in one of two studies, pain improved in one of two studies, and gas improved in one of two studies. There was no significant improvement in constipation.
  • One study looked at 40 patients using Lactobacillus acidophilus SDC 2012 and 2013 strains and found significant improvement in pain and straining, but no change in frequency of bowel movements. Another study looked at a different strain of Lactobacillus, acidophilus LB strain, in 18 patients and found improvement of symptoms after 6 weeks.
  • Two other studies looked at Lactobacillus acidophilus species in combination with other probiotics in a total of 146 patients. In one study, pain and gas improved while there was no overall difference in relief of symptoms. The second study used a combination of probiotics that also included Streptococcus thermophilus, Lactobacillus bulgaricus, and Bifidobacterium longum in 30 subjects. The probiotic mixture was significantly more effective in improving overall IBS symptoms, pain, and gas but not bloating. Another study, which also used Lactobacillus plantarum LP01, showed a decrease of overall symptoms of 55% with treatment versus 14% for placebo, but did not do any statistical testing to show this was effective.
  • Two studies looked at a combination of products containing two Lactobacillus rhamnosis strains (GG and Lc705) plus Propionibacterium freudenreichii (subspecies shermanii JS) plus a strain of Bifidobacterium, from a company named Valio, in a total of 172 patients. Both studies showed an improvement in IBS symptoms and pain but no change in constipation or diarrhea. Only one study showed an improvement in gas or quality of life.
  • Two negative studies looked at Lactobacillus reuteri ATCC 55730 in 54 subjects and Lactobacillus casei (strain GG) in 24 subjects.
  • Two studies looked at Bifidobacterium infantis 35624 (Align®) in 437 subjects. Both showed improvement in pain and IBS symptoms. One of two studies showed improved frequency of bowel movements. No improvement in overall quality of life was noted.
  • One study examined Bifidobacterium animalis DN 173010 (Activia® yogurt) in 274 patients with IBS and constipation. While the overall results were negative, when researchers confined their analysis to subjects with less than three bowel movements per week, they noted an improvement in symptoms, pain, constipation, and quality of life. However, since this analysis was done after the original study and only on a subgroup of the patients, it should not be considered conclusive.
  • Two studies looked at Escherichia coli DSM 17252 in almost 600 subjects (in one of the studies it was combined with Enterococcus faecalis DSM 16440). Both studies showed an improvement in overall symptoms and pain, while one study showed an improvement in bloating and stool consistency.
  • Another study looked at Bacillus coagulans GBI-30 6086 in 44 IBS patients with diarrhea. After treatment, abdominal pain scores were improved in 7/7 weeks in the treatment group, versus only 2/7 weeks in the placebo group. Similarly, bloating improved with treatment in 7/7 weeks versus none of 7 weeks with placebo.



Although researchers have conducted multiple studies on probiotics in patients with IBS, the results are mixed. This is not surprising, since different probiotics are like different drugs. In addition, IBS is likely due to different causes in different patients. While these early results are promising, future large trials are necessary before doctors can be confident in prescribing these agents on a routine basis.


Table 1: Statistically Significant Outcomes in Probiotic Studies of IBS Patients

Boxes show  number of positive outcomes over total number of times outcome was assessed. All studies are randomised controlled trials. QOL = quality of life.

Organism Number of studies Number of patients Overall Symptoms QOL Pain Gas/Bloat Straining Constipation Diarrhea
Lactobacillus plantarum 299V 3 112 1/2 1/2 1/2 0/1
Lactobacillus acidophilus SDC 2012, 2013 1 40 1/1 1/1 0/1
Lactobacillus acidophilus LB strain 1 18 1/1
Lactobacillus acidophilus with other probiotics 2 146 1/2 0/1 2/2 2/4 0/1
Lactobacillus rhamnosus GG with other probiotics 2 189 2/2 1/2 2/2 1/2 0/1 0/1
Bifidobacterium infantis 35624 2 436 1/1 0/1 2/2 1/1 1/1 1/2 1/2
Bifidobacterium animalis DN 173010 1 274 0/1 0/1 0/1
Escherichia coli DSM 17252 1 595 2/2 2/2 1/1 0/1 0/1
Bacillus coagulans GBI-30 6086 1 44 1/1 1/1

Subhas C Ganguli, MD, MSc, FRCPC
Assistant Professor, McMaster University
Hamilton, Ontario
First published in the Inside Tract® newsletter issue 176 – 2010