After analyzing over 40 probiotics across 69 trials, we’ve identified the most promising probiotics for improving bowel habit symptoms in IBS. Our dataset (below) is ordered based on an automated scoring system, which we further refined using additional criteria (below) to select our top choices. Here are the results of our findings.

Our Top Choice(s)

1. Unique IS-2

Two studies on Bacillus coagulans Unique IS-2 showed significant improvements in bowel habits. In the first study, conducted in children with IBS, participants saw a 71% improvement in bowel habit satisfaction, with scores dropping from 3.1 to 0.9 on a 1–5 scale, yielding a large effect size of 1.37. By week 6, about 50% of participants achieved normal stool consistency, with a moderate effect size of 0.73. (1) In the second study, conducted in adults with IBS, participants experienced a 57.6% improvement in bowel habit satisfaction, with an even larger effect size of 1.84. Additionally, 65% achieved normal stool consistency by week 6. (2) These findings earned Bacillus coagulans Unique IS-2 the #1 spot in our rankings for bowel habit improvements.

2. Bio-Kult (Multi-strain)

The multi-strain probiotic Bio-Kult improved bowel symptoms in a high-quality studyinvolving IBS-D participants. (3) The study demonstrated a statistically significant improvement in the IBS-SSS score for bowel symptoms compared to placebo, starting at month 1 and continuing through the 4-month intervention period, with effects persisting at the 5-month follow-up. By the end of month 4, the improvement was highly significant (p < 0.001), with an effect size of 0.78, securing Bio-Kult the #2 spot in our rankings for improving bowel habits.

3. DDS-1

 In a study of adults with IBS, Lactobacillus acidophilus DDS-1 was shown to improve bowel habit symptomsusing the IBS-SSS scale. By day 42, participants in the DDS-1 group experienced a 22.89-point drop in bowel symptom scores, representing a 36.3% reduction compared to the placebo group (p < 0.001), with a moderate effect size of 0.65. Additionally, 83.8% of participants (93 out of 109) had normal stool consistency by the end of the study, marking a 47.5% increase in normal stool forms and a 66.7% decrease in abnormal forms. (4) These findings earned DDS-1 the #3 spot in our rankings for improving bowel habit symptoms.

4. Symprove

In one study, participants with IBS who took Symprove saw an average improvement of 15 points in their bowel habit scores. Compared to the placebo group, the difference was 10.4 points, with a statistically significant p-value of 0.01. The effect size was 0.52, indicating a moderate improvement in bowel habits. (5) This secured Symprove the #4 spot in our rankings.

Our Criteria

The probiotics in our full database (below) are automatically ranked based on their 1) effect size for bowel habit-related symptom improvement, followed by 2) effect size for overall IBS symptoms (‘Global IBS Symptoms’), and finally by 3) the quality of evidence from the studies.

For this summary, we selected our top choices based on these rankings, along with the following additional criteria: 

• Evidence Quality Score: We only included probiotics backed by studies with an evidence quality score of 75% or higher.
• Effect Size: Only probiotics that demonstrated a moderate to high effect size (>0.5) for bowel habit-related symptom improvement made the cut.
• Clear Dosing Information: Only probiotics with clear and reliable dosing data were included.
• Commercial Availability: Probiotics needed to be commercially available to consumers.

No Direct Comparisons

It’s important to note that there are no direct comparisons between the probiotics in our database across identical study methods, so we can’t definitively rank one probiotic as superior to another. The probiotics we’ve highlighted here have shown promise for bowel habits in IBS, but as with all probiotic supplements, always consult your healthcare provider before starting.

*Population values represent the per protocol population size from studies specifically assessing the above parameters.

*Effect sizes are reported as the weighted mean effect size across studies.

References

1. Sudha MR, Jayanthi N, Aasin M, et al. Efficacy of *Bacillus coagulans* Unique IS2 in treatment of irritable bowel syndrome in children: a double-blind, randomised placebo-controlled study. *Benef Microbes.* 2018;9(4):563-572. doi:10.3920/BM2017.0129.
2.  Madempudi RS, Ahire JJ, Neelamraju J, et al. Randomized clinical trial: the effect of probiotic *Bacillus coagulans* Unique IS2 vs. placebo on the symptoms management of irritable bowel syndrome in adults. *Sci Rep.* 2019;9:12210. doi:10.1038/s41598-019-48554-x.
3. Ishaque SM, Khosruzzaman SM, Ahmed DS, Sah MP. A randomized placebo-controlled clinical trial of a multi-strain probiotic formulation (Bio-Kult®) in the management of diarrhea-predominant irritable bowel syndrome. *BMC Gastroenterol.* 2018;18(1):71. doi:10.1186/s12876-018-0788-9.
4. Martoni CJ, Srivastava S, Leyer GJ. *Lactobacillus acidophilus* DDS-1 and *Bifidobacterium lactis* UABla-12 improve abdominal pain severity and symptomology in irritable bowel syndrome: randomized controlled trial. *Nutrients.* 2020;12(2):363. doi:10.3390/nu12020363.
5. Sisson G, Ayis S, Sherwood RA, Bjarnason I. Randomised clinical trial: A liquid multi-strain probiotic vs. placebo in the irritable bowel syndrome–a 12-week double-blind study. *Aliment Pharmacol Ther.* 2014;40(1):51-62. doi:10.1111/apt.12787.

When selecting our top probiotic picks, we ensure they are commercially available and backed by high-quality evidence, with an average score above 75% for the relevant symptom parameters. The probiotics must also demonstrate a moderate to high effect size (>0.5) for these symptoms. If there are more than five candidates, we limit our top picks to the best five based on the effect size for relevant symptoms and Global IBS symptoms, as well as evidence quality. This ensures our recommendations are practical and reliable.

When selecting our top probiotic picks, we ensure they are commercially available and backed by high-quality evidence, with an average score above 75% for the relevant symptom parameters. The probiotics must also demonstrate a moderate to high effect size (>0.5) for these symptoms. If there are more than five candidates, we limit our top picks to the best five based on the effect size for relevant symptoms and Global IBS symptoms, as well as evidence quality. This ensures our recommendations are practical and reliable.