After analyzing over 40 probiotics across 69 trials, we’ve identified the most promising probiotics for managing mental health-related symptoms and diarrhea 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. Lactospore (Bacillus coagulans MTCC 5856)

Mental Health Benefits:
One small study assessed Lactospore’s effects on people with both IBS and major depressive disorder (MDD). (1) Significant improvements were seen in mental health outcomes:

• Hamilton Rating Scale for Depression (HAM-D): Scores dropped from 13.6 to 5.9 (Cohen’s d = 0.92; p = 0.029).
• Montgomery-Asberg Depression Rating Scale (MADRS): Improved from 16.3 to 6.0 (Cohen’s d = 0.93; p = 0.031).
• Center for Epidemiological Studies Depression Scale (CES-D): Decreased from 19.1 to 8 (Cohen’s d = 0.84; p < 0.01).

Other mental health parameters, such as the Clinical Global Impression (CGI) and the Gastrointestinal Discomfort Questionnaire (GI-DQ), also showed significant improvements, with the exception of dementia scores. (1)

Diarrhea Relief:
In another small study focused on IBS with diarrhea (IBS-D), Lactospore had a powerful effect on reducing diarrhea symptoms. (2) Over 90 days, participants experienced:

• A 45.1% reduction in stool frequency.
• Improved stool consistency, shifting from loose to normal form.
  The effect size for stool frequency was especially large (Cohen’s d = 2.93), making Lactospore stand out in the rankings for both mental health and diarrhea-related symptom relief. (2)

2. I.31 

Mental Health Benefits:
In one clinical trial, I.31 was tested in individuals with IBS-D. (3) Participants received either a high (10-30 billion CFU/day) or low (3-6 billion CFU/day) dose over six weeks. While neither dose significantly improved overall IBS symptoms, both led to:

• Improvements in IBS-related quality of life (IBS-QOL).
• Reductions in gut-related anxiety.
  Interestingly, the lower dose had a stronger effect (Cohen’s d = 1.00) compared to the higher dose (0.42), though the higher dose effect wasn’t statistically significant. (3)

Diarrhea Relief:
Another study on I.31 demonstrated significant improvements in stool consistency for participants with IBS-D and IBS-M (mixed), who were recruited during the diarrheal phase of their illness. (4) This probiotic had the strongest impact on diarrhea symptoms among all the probiotics in our analysis, with an impressive effect size of 3.3. However, its influence on overall IBS symptoms was neutral, which is why we ranked I.31 as #2 for managing both mental health and diarrhea symptoms in IBS. (4)

Our Criteria

The probiotics in our full database (below) are automatically ranked based on their 1) effect size for diarrhea and mental health-related symptoms, 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 mental health-related symptoms 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 highlight that there are no direct comparisons between the probiotics in our database using identical study methods. This means we can’t definitively say that one probiotic is superior to another. Both Lactospore and I.31 have shown potential in improving diarrhea and mental health-related symptoms in individuals with IBS. That said, it’s crucial to remember that probiotics should never be seen as a replacement for established treatments or medications for IBS or mental health conditions like depression. If you’re considering using probiotics or any supplements alongside conventional treatment for IBS or MDD, it’s always best to discuss it with your healthcare provider first.

*The population reported for I.31 reflects the per protocol population of both the probiotic-only study arm and the placebo group in the study by Barazza-Ortiz, as well as the full per protocol population from the study by Lorenzo-Zuniga et al.
*Effect sizes are reported as the weighted mean effect size across studies.

References

1. Majeed M, Nagabhushanam K, Arumugam S, Majeed S, Ali F. Bacillus coagulans MTCC 5856 for the management of major depression with irritable bowel syndrome: a randomised, double-blind, placebo-controlled, multi-centre, pilot clinical study. Food Nutr Res. 2018 Jul 4;62. doi: 10.29219/fnr.v62.1218. PMID: 29997457; PMCID: PMC6034030.
2. Majeed M, Nagabhushanam K, Natarajan S, et al. Bacillus coagulans MTCC 5856 supplementation in the management of diarrhea predominant Irritable Bowel Syndrome: a double-blind randomized placebo-controlled pilot clinical study. Nutr J. 2015;15:21. doi: 10.1186/s12937-016-0140-6.
3. Lorenzo-Zúñiga V, Llop E, Suárez C, et al. I.31, a new combination of probiotics, improves irritable bowel syndrome-related quality of life. World J Gastroenterol. 2014;20(26):8709–8716. doi: 10.3748/wjg.v20.i26.870.
4. Barraza-Ortiz DA, Pérez-López N, Medina-López VM, Minero-Alfaro JI, Zamarripa-Dorsey F, Fernández-Martínez NC, Llorente-Ramón A, Ramos-Aguilar GA. Combination of a probiotic and an antispasmodic increases quality of life and reduces symptoms in patients with irritable bowel syndrome: a pilot study. Dig Dis. 2021;39(3):294–300. doi: 10.1159/000510950.

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.