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Pro9.0
Probiotics Research
Likely helps
1,036 peer-reviewed studies
What the evidence says
Likely helps
Probiotics appears to help in 21 of 30 studies with measurable effects — the evidence leans clearly favourable.
Most evidence is from high-quality meta-analyses and randomised trials published 2012–2026 with a typical study size of 437 participants.
Based on 1,036 studies · 294 meta-analyses · 586 RCTs · 82,006 total participants
Confidence
High confidence
What the studies found
21helped3unclear6didn't help· 1006 more without graded effect data
By outcome
Digestive healthImproved gut microbiome balance and digestive regularity within 2-4 weeks · 2-4 weeks
Probably helps857 studies
Therapeutic & clinical
Likely helps177 studies
Women's healthProvides essential nutrients for healthy pregnancy · Ongoing
Mostly mechanism / observational91 studies
Depression & moodReductions in depression symptoms in clinical samples; anxiety benefit is inconsistent and strain-/population-dependent · 4-8 weeks
Likely helps54 studies
Glucose & metabolic
Likely helps51 studies
Weight management
Mostly mechanism / observational46 studies
Cognitive function
Likely helps40 studies
Anxiety & stressAnxiety evidence is mixed — meta-analyses are null in general populations, with benefit mainly in clinically diagnosed samples · 4-8 weeks
Likely helps28 studies
Immune supportMay reduce frequency and duration of respiratory infections · 4-8 weeks
Mostly mechanism / observational20 studies
Skin health
Mostly mechanism / observational19 studies
InflammationImproved digestion and regularity · 2-4 weeks
Probably helps18 studies
Liver health
Mostly mechanism / observational17 studies
Heart & blood pressure
Mostly mechanism / observational14 studies
Joint pain & arthritis
Mostly mechanism / observational10 studies
Cholesterol & lipids
Mostly mechanism / observational9 studies
Safety profile
Mostly mechanism / observational9 studies
Bone health
Mostly mechanism / observational8 studies
Sleep & insomnia
Mostly mechanism / observational6 studies
Energy & fatigue
Mostly mechanism / observational5 studies
Fertility & reproductive
Mostly mechanism / observational5 studies
Vision & eye health
Too few graded studies2 studies
By the numbers
Pulled from 85 studies with measurable effects
Likely real effects
85%
across studies
People studied
82k
typical study: 437 people
Strongest designs
880
294 pooled, 586 randomised
Showed benefit
70%
21/30 studies
How long studies ran
1–3 months
4
3+ months
1
Populations Studied
General population5
IBS patients3
Type 2 diabetes patients2
Cancer patients2
Active research area
1,024 studies in the last 5 years · Latest meta-analysis: 2026
201220192026
1Meta-Analysisn=703 · large study2026
Further studies with longer follow-up durations are needed to confirm these findings and explore the long-term benefits of probiotics in this population.
Chiou YY, Chiu TY, Chen MJ. · Nutrients (2026)
Background Autoimmune diseases affect 5-10% of the global population.
Subgroup analysis revealed that in rheumatoid arthritis (RA) patients, the probiotics group showed greater improvements in IL-6, IL-1β, and TNFα compared to the controls.
In multiple sclerosis (MS) patients, the probiotics group demonstrated greater improvements in hs-CRP.
2Depression symptomsMeta-AnalysisCited 23×n=1,401 · large study2025
Probiotics showed substantial reductions in depression symptoms and moderate reductions in anxiety symptoms.
Asad A et al. · Nutrition reviews (2025)
Huge benefit
← WorseNo effectBetter →
Probiotics demonstrated a significant reduction in depression symptoms (SMD: -0.96; 95% CI: -1.31, -0.61) and a moderate reduction in anxiety symptoms (SMD: -0.59; 95% CI: -0.98, -0.19).
Prebiotics did not show a significant effect on depression (SMD: -0.28; 95% CI: -0.61, 0.04).
High heterogeneity was observed across studies, and subgroup analyses indicated that study duration and probiotic formulations contributed to the variation in effect sizes.
3Periodontal pocket depth reductionMeta-AnalysisCited 16×n=1,290 · large study2024
Combining PMPR with probiotics as adjuvants to subgingival instrumentation may be more effective in improving PPD and CAL.
Mendonça CD et al. · BMC oral health (2024)
Network meta-analysis revealed significant mean differences in PPD for nine probiotic interventions, CAL for eighteen interventions, and BOP for eight interventions, with Lactobacillus demonstrating the most substantial effects.
Combining PMPR with probiotics as adjuvants to subgingival instrumentation may be more effective in improving PPD and CAL.
Lactobacillus emerged as the most comprehensive and effective among the studied probiotic.
4Pathogenic bacteria decolonizationMeta-AnalysisCited 40×n=2,871 · very large study2024
Protocol registration: PROSPERO (ID = CRD42021276045).
Rahman MN et al. · Gut microbes (2024)
Large benefit
← WorseNo effectBetter →
Likely real
This review aims to analyze available evidence from human-controlled trials to determine the effect size of probiotic interventions in decolonizing AMR pathogenic bacteria from the gut.
The persistence of pathogenic bacteria after treatment was 22%(probiotics) and 30.8%(placebo).
The pooled odds ratio was 0.59(95% CI:0.43-0.81), favoring probiotics with moderate certainty (p = 0.0001) and low heterogeneity (I2 = 49.2%, p = 0.0001).
5Intestinal barrier function improvementMeta-AnalysisCited 115×n=1,891 · large study2023
Meta-analysis of data from a total of 26 RCTs (n = 1891) indicated that probiotics significantly improved gut barrier function measured by levels of TER (MD, 5.27, 95% CI, 3.82 to 6.72, P < 0.00001), serum zonulin (SMD, -1.58, 95% CI, -2.49 to -0.66, P = 0.0007), endotoxin (SMD, -3.20, 95% CI, -5.41 to -0.98, P = 0.005), and LPS (SMD, -0.47, 95% CI, -0.85 to -0.09, P = 0.02).
Zheng Y et al. · Frontiers in Immunology (2023)
Significant improvement in intestinal barrier markers
Reduced zonulin and endotoxin levels
Enhanced gut barrier integrity across multiple trials
7FEV1 in asthma patientsMeta-AnalysisCited 10×n=1,101 · large study2023
Conclusion: the use of probiotics in patients with asthma can improve lung inflammation and asthma symptoms, reduce the number of asthma attacks, and have no effect on lung function.
Xie Q et al. · Nutricion hospitalaria (2023)
No clear effect
← WorseNo effectBetter →
Meta-analysis was performed using Revman 5.4 software and the combined effect was evaluated by odds ratio (OR) or mean difference (MD) and 95 % confidence interval (CI).
There was no significant difference in forced expiratory volume in the first second (FEV1) (MD = 0.11, 95 % CI: -0.05, 0.26) and FEV1/FVC (%) (MD = 0.32, 95 % CI: -1.48, 2.12).
Results: a total of ten references were included, all of which were randomized controlled studies, and a total of 1,101 people were investigated.
9Inflammatory bowel disease outcomesMeta-AnalysisCited 34×n=2,500 · very large study2024
Probiotics, particularly multi-strain formulations, appear efficacious for the induction of clinical remission and the prevention of relapse in UC patients as well as for relapsing pouchitis.
Estevinho MM et al. · United European Gastroenterology Journal (2024)
11Oral mucositis incidenceMeta-AnalysisCited 41×n=708 · large study2022
We recommend the use of probiotics to prevent and treat oral mucositis during cancer therapy.
Liu YC et al. · International journal of molecular sciences (2022)
Noticeable benefit
← WorseNo effectBetter →
Likely real
Three trials using Lactobacilli-based probiotics reported that the incidence of oral mucositis in the probiotic group was significantly low (risk ratio [RR] = 0.84, 95% confidence interval [CI] = 0.77−0.93, p = 0.0004).
Seven trials reported a significantly low incidence of severe oral mucositis in the probiotic group (RR = 0.65, 95% CI = 0.53−0.81, p < 0.0001).
The requirement of enteral nutrition was significantly low in the probiotic group (odds ratio = 0.34, 95% CI: 0.13−0.92, p < 0.05).
12Acute infectious diarrhoea durationMeta-AnalysisCited 110×n=12,127 · very large study2020
Probiotics probably make little or no difference to the number of people who have diarrhoea lasting 48 hours or longer, and we are uncertain whether probiotics reduce the duration of diarrhoea.
Collinson S et al. · The Cochrane database of systematic reviews (2020)
Effect size was similar in the sensitivity analysis and marked heterogeneity persisted.
Effect size was similar and marked heterogeneity persisted in pre-specified subgroup analyses of the primary outcomes that included all studies.
In six trials (433 participants) of Lactobacillus reuteri, there was consistency amongst findings (I² = 0%), but risk of bias was present in all included studies.
13Clostridium difficile-associated diarrhea preventionMeta-AnalysisCited 393×n=9,955 · very large study2017
Based on this systematic review and meta-analysis of 31 randomized controlled trials including 8672 patients, moderate certainty evidence suggests that probiotics are effective for preventing CDAD (NNTB = 42 patients, 95% CI 32 to 58).
Goldenberg JZ et al. · The Cochrane database of systematic reviews (2017)
Huge benefit
← WorseNo effectBetter →
A complete case analysis (i.e. participants who completed the study) among trials investigating CDAD (31 trials, 8672 participants) suggests that probiotics reduce the risk of CDAD by 60%.
The incidence of CDAD was 1.5% (70/4525) in the probiotic group compared to 4.0% (164/4147) in the placebo or no treatment control group (RR 0.40, 95% CI 0.30 to 0.52; GRADE = moderate).
Twenty-two of 31 trials had missing CDAD data ranging from 2% to 45%.
15ASD behavioral symptoms improvementMeta-AnalysisCited 23×n=318 · medium study2024
Our study highlighted the significant improvement in ASD behavioral symptoms through probiotic supplementation.
Soleimanpour S et al. · Journal of psychiatric research (2024)
Noticeable benefit
← WorseNo effectBetter →
Likely real
This was shown by a pooled standardized mean difference (SMD) of -0.38 (95% CI: 0.58 to -0.18, p < 0.01).
Moreover, both multi-strain probiotics and single-strain interventions showed an overall significant improvement with a SMD of -0.53 (95%CI: 0.85 to -0.22) and -0.28 (95%CI: 0.54 to -0.02), respectively.
Our study highlighted the significant improvement in ASD behavioral symptoms through probiotic supplementation.
17Anxiety symptomsMeta-Analysisn=1,527 · large study2018
Probiotics did not significantly reduce symptoms of anxiety in humans (Hedges' g = -0.12, 95% CI -0.29-0.05, p = 0.151), and did not differentially affect clinical and healthy human samples.
Reis DJ et al. · PLoS One (2018)
Probiotics reduced anxiety-like behavior in animal models, mainly in diseased animals
No significant reduction in anxiety symptoms in human clinical trials
Only L. rhamnosus showed anxiolytic effects preclinically, in under-powered analyses