After analyzing over 40 probiotics across 69 trials, we’ve identified the most promising probiotics for managing diarrhea and constipation 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 stood out as the most effective for tackling the core IBS symptoms of diarrhea, constipation, and pain. High-quality evidence from two key studies supports its benefits:

Study 1: Children with IBS

• Diarrhea: 71% reduction in urgency (scores improved from 3.1 to 0.9) after 8 weeks, with an effect size of 1.10. (1)
• Constipation: 73.3% improvement in incomplete evacuation and a 70% reduction in straining, both with effect sizes of 1.19. (1)

Study 2: Adults with IBS

• Diarrhea: 56.7% improvement in urgency (scores dropped from 3.0 to 1.3) over 8 weeks, with an effect size of 1.26. (2)
• Constipation: 61.3% reduction in incomplete evacuation and 65% improvement in straining, with effect sizes of 1.55 and 1.67, respectively. (2)

Our Criteria

The probiotics in our full database (below) are automatically ranked based on their 1) effect size for diarrhea or constipation 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 or constipation 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 and constipation 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 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 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.