After analyzing over 40 probiotics across 69 trials, we’ve identified the most promising probiotics for managing diarrhea, constipation, and gas 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)

Bacillus coagulans Unique IS-2 emerged as the most promising probiotic for managing diarrhea, constipation, and gas (flatulence), supported by high-quality evidence from two key studies.

Study 1: Children with IBS

• In an 8-week study of children with IBS, those taking Bacillus coagulans Unique IS-2 saw a 76.5% reduction in gas symptoms, with scores dropping from 3.4 to 0.8. The probiotic showed a strong effect, with an effect size of 1.21. 
• For constipation-related symptoms, incomplete evacuation improved by 73.3% (effect size: 1.19), and straining improved by 70% (effect size: 1.19). 
• Additionally, for diarrhea-related symptoms, participants reported a 71% improvement in urgency, with scores decreasing from 3.1 to 0.9 after 8 weeks. The effect size here was 1.10, indicating a strong benefit. (1)

Study 2: Adults with IBS

• In a study with adults, those taking Bacillus coagulans Unique IS-2 had a 62.5% decrease in gas symptoms, with scores decreasing from 3.2 to 1.2. This study reported an even stronger effect size of 1.72.
• Constipation symptoms also improved, with incomplete evacuation reduced by 61.3% (effect size: 1.55) and straining improving by 65% (effect size: 1.67).
• For the diarrhea-related symptom of urgency, participants saw a 56.7% improvement, with scores dropping from 3.0 to 1.3 over the same 8-week period. The effect size was 1.26, showing a notable improvement. (2)

Our Criteria

The probiotics in our full database (below) are automatically ranked based on their 1) effect size for diarrhea, constipation, and gas relief, 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 diarrhea, constipation, and gas relief 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. Bacillus coagulans Unique IS-2 shows promise for diarrhea, constipation, and gas relief 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 a gas-related parameter.
*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 the 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.

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.