Probiotics

Probiotics: Effective Strains, Clinical Evidence, and Health Applications

Probiotics are live microorganisms investigated for their potential to influence the intestinal and other human microbiomes and improve specific health outcomes. Clinical research increasingly demonstrates that probiotics should not be treated as a single therapeutic category. Effects observed with one organism, strain, dose, or formulation cannot automatically be assumed to apply to another.

A central lesson from probiotic research is therefore the importance of identifying organisms at the strain level. Names such as Lacticaseibacillus rhamnosus GG, Limosilactobacillus reuteri DSM 17938, Bifidobacterium longum 35624, and Lactiplantibacillus plantarum 299v identify preparations that have been evaluated in specific clinical settings. Simply knowing that a product contains a Lactobacillus or Bifidobacterium species is generally insufficient to determine whether it has demonstrated clinical effectiveness.

The research summarized here ranges from randomized controlled trials to systematic reviews, network meta-analyses, and umbrella reviews. Evidence is strongest for certain gastrointestinal applications, while research into neurological, metabolic, dermatological, autoimmune, respiratory, urogenital, and other conditions remains more variable.

Strain-Specific Evidence Matters

One of the most important developments in probiotic science is recognition that clinical effects are often strain-specific. Two microorganisms belonging to the same species may differ in their ability to survive gastrointestinal transit, interact with intestinal cells, alter microbial communities, produce metabolites, influence immune signaling, or produce measurable clinical outcomes.

This creates an important distinction between evidence for "probiotics" generally and evidence for an identified probiotic strain. Clinical studies increasingly emphasize the complete strain designation when evaluating effectiveness.

Several probiotic strains appearing repeatedly in the clinical literature include:

Lacticaseibacillus rhamnosus GG (LGG)
Saccharomyces boulardii, including CNCM I-745
Limosilactobacillus reuteri DSM 17938
Bifidobacterium longum 35624
Lactiplantibacillus plantarum 299v (DSM 9843)
Bacillus coagulans Unique IS2
Bacillus coagulans MTCC 5856
Bifidobacterium animalis subsp. lactis HN019
Bifidobacterium animalis subsp. lactis BB-12
Lactobacillus acidophilus NCFM
Lactobacillus casei Shirota
Lactobacillus crispatus CTV-05
Lacticaseibacillus paracasei CNCM I-1518

The evidence for these strains varies considerably by condition.

Antibiotic-Associated Diarrhea

Antibiotic-associated diarrhea is among the better-supported clinical applications for certain probiotics. Antibiotic treatment can disrupt intestinal microbial communities, sometimes producing diarrhea during or shortly after therapy.

Lacticaseibacillus rhamnosus GG, commonly called LGG, has been evaluated in randomized trials, systematic reviews, and meta-analyses involving both children and adults. Multiple analyses have found reductions in antibiotic-associated diarrhea, although the magnitude and certainty of benefit vary among populations and studies.

The probiotic yeast Saccharomyces boulardii also has a substantial clinical literature. Meta-analyses and randomized trials have reported reductions in antibiotic-associated diarrhea among children and adults. The strain CNCM I-745 is specifically identified in some clinical literature.

These findings also illustrate why probiotic recommendations should specify the organism or strain rather than simply suggesting an unspecified probiotic supplement.

Infantile Colic

Limosilactobacillus reuteri DSM 17938 is one of the most extensively studied probiotic strains for infantile colic.

Randomized controlled trials have reported reductions in crying and fussing among breastfed infants receiving DSM 17938. An individual-participant-data meta-analysis also found reductions in crying duration and increased treatment response among breastfed infants.

The evidence is considerably less certain for formula-fed infants. This difference illustrates that probiotic effectiveness may depend not only on strain but also on characteristics of the population receiving it.

Bifidobacterium animalis subsp. lactis BB-12 has also been investigated for infantile colic, with research reporting reductions in crying and fussing.

Irritable Bowel Syndrome

Irritable bowel syndrome is one of the most extensively studied areas of probiotic research, but it is also one of the clearest examples of heterogeneous results.

Systematic reviews generally suggest that some probiotic strains and combinations can improve IBS symptoms, but effectiveness differs considerably among preparations. Studies vary in IBS subtype, dose, strain, duration, and outcome measurement.

Bifidobacterium longum 35624

Bifidobacterium longum 35624, historically described as Bifidobacterium infantis 35624, has been evaluated in clinical trials involving IBS.

Research has reported improvements in abdominal pain, bloating, bowel dysfunction, incomplete evacuation, straining, and global IBS symptoms at particular doses. Strain-specific systematic reviews continue to identify 35624 among probiotics with evidence for certain IBS outcomes.

Lactiplantibacillus plantarum 299v

Lactiplantibacillus plantarum 299v, also designated DSM 9843, has produced favorable results in several IBS trials, including reductions in abdominal pain and bloating and improvements in global symptoms.

The evidence is not uniform, however. At least one randomized study found no significant improvement in abdominal pain or bloating compared with placebo. Such conflicting findings reinforce the need to evaluate the complete clinical literature rather than relying on a single positive study.

Bacillus coagulans Unique IS2

Bacillus coagulans Unique IS2 has been studied in adults and children with IBS. Randomized trials have reported improvements in abdominal pain, bloating, stool characteristics, urgency, incomplete evacuation, and overall bowel satisfaction.

Network meta-analysis has also identified Unique IS2 among stronger-performing probiotic interventions for certain IBS outcomes.

Bacillus coagulans MTCC 5856

Bacillus coagulans MTCC 5856 has been studied particularly in diarrhea-predominant IBS. A randomized placebo-controlled trial reported improvements in IBS symptoms and quality-of-life measures after supplementation.

Constipation and Gastrointestinal Transit

Several identified probiotic strains have been investigated for functional constipation and gastrointestinal transit.

Bifidobacterium animalis subsp. lactis HN019 has been evaluated in randomized trials examining whole-gut transit time, spontaneous bowel movements, stool consistency, straining, and other constipation-related outcomes.

Bacillus coagulans Unique IS2 has also been studied for functional constipation, with clinical research reporting increases in spontaneous bowel movements and reductions in constipation symptoms.

Lactobacillus casei Shirota appears in systematic reviews of chronic constipation and has been associated in some studies with improved defecation frequency and stool consistency.

The results across constipation studies nevertheless remain heterogeneous, and effectiveness should not be generalized to every probiotic strain.

Functional Bowel Symptoms

Lactobacillus acidophilus NCFM has been studied in IBS and other functional bowel disorders.

Research involving NCFM alone or combined with Bifidobacterium lactis Bi-07 has examined abdominal pain, bloating, IBS symptom severity, and mechanisms involving gastrointestinal sensory pathways.

Some studies have reported improvements, particularly in bloating and symptom severity, but evidence remains less extensive than for some of the better-established gastrointestinal strains.

Inflammatory Bowel Disease

Probiotics have been extensively investigated in inflammatory bowel disease, particularly ulcerative colitis.

Systematic reviews and meta-analyses suggest that certain probiotic formulations may help induce remission, maintain remission, or reduce recurrence in ulcerative colitis. Results for Crohn's disease have generally been less convincing.

The effectiveness of probiotic interventions in inflammatory bowel disease appears strongly dependent on disease subtype and formulation. Evidence for one preparation should therefore not be generalized to all probiotics.

Liver Disease and Hepatic Encephalopathy

Research has examined probiotics in liver cirrhosis and complications such as minimal hepatic encephalopathy.

Meta-analyses have reported possible improvements in blood ammonia, cognitive measures, liver function, intestinal microbiota, and reversal of minimal hepatic encephalopathy. Some randomized trials have also found reductions in development of overt hepatic encephalopathy.

The proposed mechanisms center on interactions between the intestinal microbiome and liver, sometimes described as the gut-liver axis. Alterations in microbial metabolism and intestinal barrier function may influence compounds reaching the liver through portal circulation.

Probiotics have also been studied in nonalcoholic fatty liver disease, with meta-analyses examining liver enzymes, metabolic measures, inflammation, and insulin resistance.

Recurrent Urinary Tract Infections and Urogenital Health

The urogenital microbiome is another area of probiotic research.

Lactobacillus crispatus CTV-05 has been investigated as a possible intervention for recurrent urinary tract infection in women. Other studies have examined oral and vaginal combinations of Lactobacillus strains.

Research involving recurrent urinary tract infections remains mixed, with some randomized trials reporting reductions in symptomatic recurrence and systematic reviews finding that many studies remain inconclusive.

Probiotics have also been studied in bacterial vaginosis. Meta-analyses have compared probiotics alone, antibiotics alone, and combined antibiotic-probiotic treatment. Findings suggest possible benefit in some settings but do not establish all probiotic preparations as effective treatments.

Respiratory and Infectious Disease

Lacticaseibacillus paracasei CNCM I-1518 has been studied for common respiratory and gastrointestinal infections.

Systematic reviews of randomized trials suggest that certain probiotic preparations may reduce the incidence or number of common infectious illnesses. Effects on duration and severity appear less consistent.

Broader research has also examined probiotics in respiratory infections, pediatric asthma, COVID-19, and post-COVID dysbiosis. These areas remain more exploratory than the evidence supporting certain gastrointestinal applications.

Oral and Periodontal Health

Probiotics have been investigated in dental caries, periodontal disease, gingivitis, halitosis, peri-implant disease, and the broader oral microbiome.

Systematic reviews and umbrella reviews have reported possible benefits for periodontal pocket depth, bleeding on probing, clinical attachment, and some microbial outcomes.

Lactobacillus reuteri has been studied as an adjunct to scaling and root planing for periodontal disease. However, oral probiotic studies use numerous strains and delivery systems, making it difficult to identify universally effective preparations.

Allergic and Dermatological Conditions

Probiotic interventions have been investigated for atopic dermatitis, allergic rhinitis, acne, psoriasis, and other inflammatory skin and allergic disorders.

Studies of atopic dermatitis show that results may differ considerably among probiotic species and strains. Some systematic reviews and meta-analyses report reductions in severity scores, while others emphasize inconsistency among trials.

Research into allergic rhinitis likewise suggests possible improvements in symptoms or quality of life, but strain-specific systematic reviews have found that results for individual preparations are often inconclusive.

In acne and psoriasis, growing interest centers on possible relationships between intestinal microbes, systemic inflammation, immune activity, and skin disease—the so-called gut-skin axis. Current evidence suggests possible adjunctive roles for probiotics, but the research remains less established than for antibiotic-associated diarrhea or certain gastrointestinal disorders.

Metabolic Health, Obesity, and PCOS

Probiotics and synbiotics have been studied for obesity, metabolic syndrome, cholesterol, insulin resistance, and polycystic ovary syndrome.

Meta-analyses involving overweight and obese populations report small changes in body weight, BMI, waist circumference, lipid measurements, blood glucose, and other cardiovascular or metabolic markers.

In PCOS, randomized trials have examined insulin resistance, reproductive hormones, triglycerides, inflammation, oxidative stress, and body composition. Some favorable metabolic and hormonal changes have been reported, but findings are not sufficiently uniform to treat probiotics as a replacement for established PCOS therapies.

Neurological Health and the Gut-Brain Axis

Increasing research investigates communication between the intestinal microbiome and central nervous system, often referred to as the microbiota-gut-brain axis.

Probiotic interventions have been studied in Parkinson's disease, Alzheimer's disease, mild cognitive impairment, migraine, multiple sclerosis, depression, anxiety, and other neurological or psychiatric conditions.

In Parkinson's disease, studies have examined constipation, gastrointestinal symptoms, inflammatory markers, motor and non-motor symptoms, and quality of life.

Studies of Alzheimer's disease and cognitive impairment have produced mixed findings. Some analyses suggest possible improvements in cognitive performance, while others find no significant overall effect.

Migraine studies have also investigated probiotics alone or together with nutritional supplements, with some reports of fewer headache days or reduced severity.

Overall, neurological applications remain promising but substantially more preliminary than established gastrointestinal indications.

Autoimmune and Inflammatory Diseases

The intestinal microbiome has been investigated as a potential contributor to immune regulation and autoimmune disease.

Research summarized in the literature includes rheumatoid arthritis, multiple sclerosis, systemic lupus erythematosus, psoriasis, and other inflammatory disorders.

Some probiotic studies report reductions in inflammatory markers or modest improvements in disease-related outcomes. However, much of this literature remains heterogeneous, and some areas—particularly systemic lupus erythematosus—include substantial preclinical rather than human clinical evidence.

These findings should therefore be regarded as emerging research rather than established probiotic treatment indications.

Chronic Kidney Disease and the Gut-Kidney Axis

Research into chronic kidney disease increasingly examines interactions between intestinal microorganisms, inflammation, microbial metabolites, and kidney function.

Probiotics and synbiotics have been investigated as possible methods of changing intestinal microbial activity and reducing production of gut-derived uremic compounds.

Systematic reviews have examined kidney-function markers, inflammation, metabolic products, and outcomes among patients receiving dialysis. Clinical evidence remains developing and is not yet sufficient to regard probiotics as established therapy for chronic kidney disease.

Bone Health and Menopause

Probiotics have also been investigated for bone mineral density, osteoporosis, and menopausal health.

Studies in postmenopausal women suggest possible effects on bone mineral density, particularly in women with osteopenia. Proposed mechanisms include altered mineral absorption, inflammation, intestinal permeability, and microbial metabolite production.

Research in peri- and postmenopausal women also examines vaginal microbiota, urogenital health, menopausal symptoms, and interactions with other treatments.

These potential uses remain adjunctive and should not be considered replacements for established prevention or treatment of osteoporosis or menopausal conditions.

Celiac Disease

The intestinal microbiome has been investigated as a possible modifier of celiac disease.

Research into probiotic bifidobacteria examines mechanisms involving gluten-derived peptides, intestinal barrier function, inflammation, and immune responses.

Some studies suggest that particular strains may influence gastrointestinal symptoms or inflammatory activity, but the evidence remains limited. A strict gluten-free diet remains the fundamental management strategy represented in the research literature.

The Importance of Evidence Quality

The probiotic literature contains randomized controlled trials, systematic reviews, meta-analyses, network meta-analyses, observational studies, mechanistic studies, and experimental research.

These forms of evidence should not be treated as equivalent. Systematic reviews may identify apparent benefits while simultaneously reporting high heterogeneity, small sample sizes, publication bias, inconsistent formulations, or low certainty of evidence.

Positive findings should therefore be interpreted according to several questions:

Was the probiotic identified at the strain level?
Was the intervention tested in randomized controlled trials?
Was the same strain evaluated in more than one independent study?
Was the outcome clinically meaningful?
Was the effect replicated in systematic reviews or meta-analyses?
Were findings consistent across studies?
Did treatment benefit a particular subgroup rather than the entire population?
Was the probiotic administered alone or as part of a multi-strain or synbiotic formulation?
What dose and treatment duration were used?
Were there clinically important adverse events?

These distinctions are essential when translating probiotic research into practical conclusions.

Probiotics Are Not Interchangeable

One of the strongest conclusions supported by the collected research is that the word "probiotic" is too broad to function as a meaningful description of effectiveness.

A clinical benefit demonstrated for Lacticaseibacillus rhamnosus GG cannot automatically be attributed to another Lacticaseibacillus rhamnosus strain. Likewise, evidence concerning Limosilactobacillus reuteri DSM 17938 does not prove that every L. reuteri product will produce the same result.

Multi-strain supplements introduce additional complexity. A product containing many strains is not necessarily more effective than a carefully studied single-strain product. Clinical evidence must relate as closely as possible to the actual formulation being used.

Consumers and clinicians therefore benefit from looking beyond broad marketing terms such as "10-strain probiotic," "50 billion CFU," or "gut health probiotic." The scientifically relevant questions are which strains are present, whether that exact strain or formulation has been studied, what condition was studied, at what dose, and with what outcome.

Areas With Comparatively Stronger Evidence

The uploaded research suggests several areas in which particular probiotic strains have comparatively substantial clinical support.

Lacticaseibacillus rhamnosus GG and Saccharomyces boulardii have repeatedly been studied for prevention of antibiotic-associated diarrhea.

Limosilactobacillus reuteri DSM 17938 has relatively strong evidence for reducing infantile colic symptoms among breastfed infants.

Several specific strains—including Bifidobacterium longum 35624, Lactiplantibacillus plantarum 299v, and certain Bacillus coagulans strains—have demonstrated benefits for particular IBS outcomes, although IBS evidence remains heterogeneous.

Bifidobacterium animalis subsp. lactis HN019 and several other strains have been investigated for constipation and intestinal transit.

These examples demonstrate that the most defensible claims about probiotics are usually narrow ones: a particular strain, given at a particular dose, to a particular population, for a particular clinical outcome.

Areas Where Evidence Remains Emerging

A much larger group of possible probiotic applications remains under investigation.

These include neurological disorders, cognitive decline, migraine, rheumatoid arthritis, lupus, chronic kidney disease, obesity, metabolic syndrome, PCOS, osteoporosis, acne, psoriasis, respiratory disease, kidney stones, celiac disease, COVID-19, and other conditions.

Systematic reviews in many of these areas identify potentially favorable effects. However, positive biological signals or statistically significant changes do not necessarily establish probiotics as effective clinical treatments.

Many fields still require larger randomized trials, standardized strains and doses, longer follow-up, replication by independent researchers, and clearer measurements of meaningful clinical outcomes.

Conclusion

Probiotic research has evolved from the broad idea of consuming "beneficial bacteria" toward a more precise understanding in which clinical effects depend heavily on the organism, strain, formulation, dose, population, and condition being treated.

Some of the most convincing evidence concerns specific strains used for defined gastrointestinal indications. Lacticaseibacillus rhamnosus GG and Saccharomyces boulardii have substantial evidence for antibiotic-associated diarrhea, while Limosilactobacillus reuteri DSM 17938 has demonstrated benefits for infantile colic in breastfed infants. Particular strains of Bifidobacterium, Lactiplantibacillus, and Bacillus have also produced favorable results in IBS and constipation research.

Beyond these better-studied applications, probiotics are being investigated across a remarkable range of conditions involving metabolism, immunity, neurological function, skin disease, liver health, oral health, reproductive health, and the gut-brain, gut-liver, gut-kidney, and gut-skin axes.

The evidence does not support treating all probiotics as equivalent. Instead, the strongest interpretation of the research is that probiotic effectiveness is often strain-specific and indication-specific. A probiotic should therefore be judged by evidence for the exact organism or formulation and the exact clinical outcome under consideration, rather than by the general reputation of probiotics as a category.

Lacticaseibacillus rhamnosus GG (LGG) — Antibiotic-Associated Diarrhea

| Researchers | Journal of Clinical Gastroenterology | 2018

A network meta-analysis involving more than 9,000 participants compares different probiotics for prevention of antibiotic-associated diarrhea. Lactobacillus rhamnosus GG had the highest probability of ranking among the most effective and best-tolerated probiotic interventions.

| V. Agamennone et al. | European Journal of Clinical Pharmacology | 2018

A strain-specific analysis of probiotic preparations used to prevent antibiotic-associated diarrhea identifies seven effective formulations. Lactobacillus rhamnosus GG produced one of the strongest effects, with substantially less antibiotic-associated diarrhea than placebo.

| C. Mantegazza et al. | Nutrients | 2018

A clinical review of probiotics for pediatric antibiotic-associated diarrhea finds the strongest strain-specific evidence for Lactobacillus rhamnosus GG and Saccharomyces boulardii. The authors emphasize that results obtained with these strains should not be generalized to other probiotics.

| Hania Szajewska et al. | Journal of Pediatric Gastroenterology and Nutrition | 2016

Evidence-based recommendations from the European Society for Pediatric Gastroenterology, Hepatology and Nutrition identify Lactobacillus rhamnosus GG as one of the probiotic strains with sufficient evidence to recommend for preventing antibiotic-associated diarrhea in children.

| Hania Szajewska and Marek Kołodziej | Alimentary Pharmacology & Therapeutics | 2015

A strain-specific systematic review and meta-analysis evaluates Lactobacillus rhamnosus GG, commonly abbreviated LGG, for prevention of antibiotic-associated diarrhea. LGG significantly reduced antibiotic-associated diarrhea in children and adults, although the certainty of evidence was rated moderate to low. This is one of the better-supported strain-specific uses of probiotics.

| Lynne V. McFarland | Annals of Nutrition and Metabolism | 2015

A strain-specific review of probiotics for pediatric antibiotic-associated diarrhea finds significant preventive effects for Lactobacillus rhamnosus GG as well as Saccharomyces boulardii.

| Jason Hawrelak et al. | Digestive Diseases and Sciences | 2005

A systematic review evaluates Lactobacillus rhamnosus GG specifically for preventing antibiotic-associated diarrhea. Four of six qualifying clinical trials reported a significant reduction in diarrhea risk, while another showed fewer days with antibiotic-associated diarrhea.

Saccharomyces boulardii — Antibiotic-Associated Diarrhea

| M. Storr et al. | Medizinische Klinik | 2021

A clinical review emphasizes that prevention of antibiotic-associated diarrhea is strain-specific. The authors identify Saccharomyces boulardii CNCM I-745 and Lactobacillus rhamnosus GG as evidence-based options rather than recommending probiotics as a general category.

| Hania Szajewska and Marek Kołodziej | Alimentary Pharmacology & Therapeutics | 2015

A systematic review and meta-analysis evaluates the probiotic yeast Saccharomyces boulardii specifically for antibiotic-associated diarrhea. Supplementation significantly reduced the risk of antibiotic-associated diarrhea among both children and adults.

| Lynne V. McFarland | World Journal of Gastroenterology | 2010

A large systematic review examines Saccharomyces boulardii across multiple gastrointestinal disorders. Twenty-seven randomized controlled studies involving more than 5,000 participants were analyzed, with particularly strong evidence for prevention of antibiotic-associated diarrhea.

| Lynne V. McFarland | American Journal of Gastroenterology | 2006

A meta-analysis evaluates probiotics for antibiotic-associated diarrhea and Clostridium difficile disease. Saccharomyces boulardii and Lactobacillus rhamnosus GG were among the probiotic interventions significantly associated with prevention of antibiotic-associated diarrhea.

| Hania Szajewska and Jacek Mrukowicz | Alimentary Pharmacology & Therapeutics | 2005

A strain-focused meta-analysis of randomized controlled trials finds Saccharomyces boulardii moderately effective for preventing antibiotic-associated diarrhea in children and adults.

| M. Kotowska et al. | Alimentary Pharmacology & Therapeutics | 2005

A randomized placebo-controlled trial evaluates Saccharomyces boulardii for preventing antibiotic-associated diarrhea in children. Children receiving the probiotic developed substantially less antibiotic-associated diarrhea than those receiving placebo.

Limosilactobacillus reuteri DSM 17938 — Infantile Colic

| Valerie Sung et al. | Pediatrics | 2018

An individual-participant-data meta-analysis evaluates Lactobacillus reuteri DSM 17938 specifically for infantile colic. DSM 17938 reduced crying duration and increased treatment response among breastfed infants. Evidence was insufficient to reach the same conclusion for formula-fed infants.

| P. Gutiérrez-Castrellón et al. | Medicine | 2017

A network meta-analysis compares treatments for infantile colic. Lactobacillus reuteri DSM 17938 was among the interventions associated with meaningful reductions in infant colic symptoms.

| K. Chau et al. | Journal of Pediatrics | 2015

A randomized double-blind placebo-controlled Canadian trial finds that Lactobacillus reuteri DSM 17938 significantly reduces crying and fussing among breastfed infants with colic.

| G. L. Mi et al. | PLoS ONE | 2015

A randomized trial examines Lactobacillus reuteri DSM 17938 for infantile colic. Supplementation reduced daily crying duration and was associated with higher parental satisfaction compared with the control treatment.

| Hania Szajewska et al. | Journal of Pediatrics | 2013

A randomized controlled trial evaluates Lactobacillus reuteri DSM 17938 in exclusively or predominantly breastfed infants with colic. Infants receiving DSM 17938 experienced greater reductions in crying time than those receiving placebo.

| Francesco Savino et al. | Pediatrics | 2010

A randomized controlled trial administers Lactobacillus reuteri DSM 17938 to breastfed infants with colic. A dose of 100 million CFU per day reduced crying and improved colic symptoms compared with placebo.

Bifidobacterium longum 35624 — IBS

| R. Maslennikov et al. | PubMed | 2026

A strain-specific systematic review and meta-analysis identifies Bifidobacterium longum 35624, formerly classified as Bifidobacterium infantis 35624, among the individual probiotic strains showing efficacy for important IBS symptoms.

| Darren M. Brenner et al. | Reviews in Gastroenterological Disorders | 2009

A focused review examines Bifidobacterium infantis 35624 as a treatment for IBS. Two randomized controlled trials had demonstrated improvements in individual and global IBS symptoms without an apparent increase in adverse events.

| Darren M. Brenner et al. | American Journal of Gastroenterology | 2009

A systematic review of probiotics for IBS identifies Bifidobacterium infantis 35624 as one of the strains supported by appropriately designed randomized controlled studies. Trials reported improvements in abdominal pain, bloating, and bowel-related symptoms.

| Peter J. Whorwell et al. | American Journal of Gastroenterology | 2006

A large randomized controlled trial evaluates Bifidobacterium infantis 35624 in women with irritable bowel syndrome. One tested dose significantly improved abdominal pain, bloating, bowel dysfunction, incomplete evacuation, straining, and global IBS symptoms compared with placebo.

| Liam O’Mahony et al. | Gastroenterology | 2005

A randomized clinical trial compares Bifidobacterium infantis 35624 with another probiotic and placebo in IBS. Strain 35624 improved IBS symptoms and was associated with normalization of a measure of pro- versus anti-inflammatory immune signaling.

Lactiplantibacillus plantarum 299v (DSM 9843) — IBS

| H. Krammer et al. | Zeitschrift für Gastroenterologie | 2021

A clinical study evaluates Lactobacillus plantarum 299v for irritable bowel syndrome. Treatment was associated with significant improvement in global IBS symptoms and quality of life.

| C. Stevenson et al. | Nutrition | 2014

A randomized trial provides an important counterpoint to positive studies of strain 299v. Eight weeks of Lactobacillus plantarum 299v did not significantly improve abdominal pain or bloating compared with placebo, demonstrating that even a promising strain does not produce uniform results across trials.

| Philippe Ducrotté et al. | World Journal of Gastroenterology | 2012

A randomized double-blind placebo-controlled trial evaluates Lactobacillus plantarum 299v, also designated DSM 9843, in adults with IBS. Four weeks of treatment improved overall symptoms, with particularly notable reductions in abdominal pain and bloating.

| K. Niedzielin et al. | European Journal of Gastroenterology & Hepatology | 2001

An early double-blind randomized controlled trial evaluates Lactobacillus plantarum 299v in people with IBS. Participants receiving 299v reported substantially greater global improvement in IBS symptoms than those receiving placebo.

Bacillus coagulans Unique IS2 — IBS and Functional Constipation

| P. Xie et al. | Nutrients | 2023

A strain-level network meta-analysis compares individual probiotics for IBS outcomes. Bacillus coagulans Unique IS2 ranked among the strongest-performing interventions for abdominal pain.

| R. S. Madempudi et al. | Beneficial Microbes | 2020

A randomized double-blind placebo-controlled study evaluates Bacillus coagulans Unique IS2 in adults with functional constipation. Supplementation increased spontaneous bowel movements and reduced several constipation-related symptoms compared with placebo.

| R. S. Madempudi et al. | Scientific Reports | 2019

A randomized double-blind placebo-controlled trial evaluates Bacillus coagulans Unique IS2 in adults with IBS. The strain produced significant improvements in abdominal pain and several other IBS symptoms compared with placebo.

| M. Ratna Sudha et al. | Beneficial Microbes | 2018

A randomized placebo-controlled trial evaluates Bacillus coagulans Unique IS2 in children ages four through twelve with IBS. The strain significantly reduced pain intensity and improved abdominal discomfort, bloating, stool consistency, urgency, incomplete evacuation, and overall bowel satisfaction.

Bacillus coagulans MTCC 5856 — Diarrhea-Predominant IBS

| Muhammed Majeed et al. | Nutrition Journal | 2016

A randomized double-blind placebo-controlled trial evaluates Bacillus coagulans MTCC 5856 in adults with diarrhea-predominant IBS. Ninety days of supplementation improved several IBS symptoms and quality-of-life measures compared with placebo.

Bifidobacterium animalis subsp. lactis HN019 — Constipation and Gut Transit

| J. Cheng et al. | American Journal of Gastroenterology | 2024

An eight-week randomized trial further evaluates Bifidobacterium animalis subsp. lactis HN019 in adults with constipation, adding to the clinical literature concerning this strain and bowel-movement frequency.

| A. Ibarra et al. | Gut Microbes | 2018

A randomized controlled trial evaluates Bifidobacterium animalis subsp. lactis HN019 in 228 adults with functional constipation. Two daily doses were studied for effects on complete spontaneous bowel movements, stool consistency, straining, and related symptoms.

| P. A. Waller et al. | Scandinavian Journal of Gastroenterology | 2011

A randomized clinical trial examines different doses of Bifidobacterium lactis HN019. Supplementation shortened whole-gut transit time and improved the frequency of gastrointestinal symptoms.

Bifidobacterium animalis subsp. lactis BB-12 — Infantile Colic

| K. Chen et al. | Nutrients | 2021

A clinical study evaluates Bifidobacterium animalis subsp. lactis BB-12 in infants diagnosed with colic. BB-12 supplementation reduced crying and fussing.

Lactobacillus acidophilus NCFM — IBS and Functional Bowel Symptoms

| Anna Lyra et al. | World Journal of Gastroenterology | 2016

A randomized placebo-controlled study evaluates Lactobacillus acidophilus NCFM in people with irritable bowel syndrome. NCFM supplementation was associated with improvements in IBS symptom severity in some participants.

| T. Ringel-Kulka et al. | Alimentary Pharmacology & Therapeutics | 2014

A randomized clinical study examines Lactobacillus acidophilus NCFM in people with functional abdominal pain.

| T. Ringel-Kulka et al. | Journal of Clinical Gastroenterology | 2011

A randomized controlled trial evaluates Lactobacillus acidophilus NCFM together with Bifidobacterium lactis Bi-07 in patients with functional bowel disorders. The probiotic treatment significantly improved bloating compared with placebo.

Lactobacillus casei Shirota — Constipation

| A. van der Schoot et al. | Clinical Nutrition | 2022

A systematic review and meta-analysis examines individual probiotics and synbiotics for chronic constipation in adults. Lactobacillus casei Shirota was among the specifically identified strains studied.

| M. M. Araújo et al. | Nutrients | 2022

A systematic review identifies Lactobacillus casei Shirota as one of the better-studied individual strains for chronic constipation.

| Anna Chmielewska and Hania Szajewska | World Journal of Gastroenterology | 2010

A systematic review reports favorable adult evidence for Lactobacillus casei Shirota, particularly for defecation frequency and stool consistency.

Lactobacillus crispatus CTV-05 — Recurrent Urinary Tract Infection

| Matthew E. Falagas et al. | Drugs | 2006

A systematic review identifies Lactobacillus crispatus CTV-05 among strains showing promising preventive effects for recurrent urinary tract infection in women.

Lacticaseibacillus paracasei CNCM I-1518 — Respiratory and Gastrointestinal Infections

| M. Strauss et al. | Frontiers in Nutrition | 2021

A systematic review evaluates individual probiotic strains for prevention of acute respiratory tract infections. Lacticaseibacillus paracasei CNCM I-1518 is among the strains supported by randomized placebo-controlled studies.

| Theresa Poon et al. | Nutrients | 2020

A systematic review and meta-analysis of nine randomized trials evaluates a fermented dairy preparation containing Lacticaseibacillus paracasei CNCM I-1518 together with yogurt cultures.

Probiotics and Parkinson’s Disease

| X. Gu et al. | PubMed | 2025

A systematic review and meta-analysis evaluates therapies targeting the intestinal microbiota in Parkinson’s disease.

| V. Leta et al. | PubMed | 2025

A clinical study evaluates a four-strain probiotic in people with Parkinson’s disease.

| E. S. Atak et al. | PubMed / Basic and Clinical Neuroscience | 2024

A systematic review of randomized controlled trials evaluates potential therapeutic targets of probiotics in Parkinson’s disease.

| X. Jin et al. | PubMed | 2024

A systematic review and meta-analysis evaluates probiotic supplements in Parkinson’s disease.

| A. M. Mincic et al. | PubMed | 2024

A review evaluates manipulation of the intestinal microbiome in neurodegenerative disorders including Parkinson’s disease, Alzheimer’s disease, multiple sclerosis, and amyotrophic lateral sclerosis.

| A. I. Beltrán-Velasco et al. | PubMed | 2024

A systematic review examines Lactiplantibacillus plantarum as a potential intervention for neurodegenerative diseases.

Probiotics, Alzheimer’s Disease, and Cognitive Function

| S. Tripathi et al. | PubMed | 2024

A systematic review and meta-analysis evaluates individual cognitive domains in people with mild cognitive impairment and Alzheimer’s disease.

| F. Zhu et al. | PubMed | 2024

A systematic analysis examines probiotic interventions across neurodegenerative diseases.

| R. Mo et al. | PubMed | 2024

A meta-analysis investigates probiotic supplementation in people with Alzheimer’s disease and mild cognitive impairment.

| E. Akbari et al. | Frontiers in Aging Neuroscience | 2016

A randomized double-blind controlled trial investigates probiotic supplementation in people with Alzheimer’s disease.

Probiotics and Polycystic Ovary Syndrome

| D. M. Guevara et al. | PubMed | 2024

A systematic review of randomized clinical trials evaluates probiotics, prebiotics, and synbiotics in women with polycystic ovary syndrome.

| S. Salehi et al. | PubMed | 2024

A review examines alterations of the intestinal microbiota in polycystic ovary syndrome.

| S. Alesi et al. | PubMed | 2022

A comprehensive review examines nutritional supplements and complementary therapies in PCOS.

| M. Samimi et al. | PubMed | 2019

A randomized controlled trial evaluates synbiotic supplementation in women with PCOS.

| M. Karamali et al. | PubMed | 2018

A randomized trial evaluates probiotic supplementation and hormonal profiles in women with PCOS.

| S. Ahmadi et al. | PubMed | 2017

A clinical trial examines probiotic supplementation in women with PCOS.

Probiotics and Liver Cirrhosis

| Y. L. Zhou et al. | PubMed | 2024

A meta-analysis evaluates probiotics for minimal hepatic encephalopathy.

| Y. Pan et al. | PubMed | 2024

A systematic analysis compares probiotics, prebiotics, and synbiotics for liver-related outcomes.

| Researchers | PubMed | 2024

A systematic review evaluates probiotics in cirrhosis complicated by portal hypertension.

| Xing Yang et al. | Frontiers in Medicine | 2024

A systematic review and meta-analysis of 30 randomized studies evaluates probiotics in liver cirrhosis.

| I. D. N. Wibawa et al. | PubMed | 2023

A systematic review and meta-analysis examines probiotics for minimal hepatic encephalopathy.

| L. Huang et al. | PubMed | 2022

A review examines alterations of the intestinal microbiome in cirrhosis and the effects of probiotic supplementation.

| M. K. Lunia et al. | PubMed | 2014

A randomized controlled trial investigates probiotics for preventing hepatic encephalopathy in patients with cirrhosis.

Probiotics and Acne

| H. W. Lin et al. | PubMed | 2025

A systematic review and meta-analysis evaluates oral probiotics for acne vulgaris.

| I. A. M. P. Sutema et al. | PubMed | 2025

A systematic review examines oral and topical probiotic treatments for acne and skin health.

| A. Podwojniak et al. | PubMed | 2025

A systematic review examines acne and the cutaneous microbiome.

| A. Boby et al. | Archives of Dermatological Research | 2024

A systematic review assesses probiotics for treating acne vulgaris.

| A. Goodarzi et al. | PubMed | 2020

A review explores probiotics as adjunctive therapy for acne vulgaris.

Probiotics and Psoriasis

| Y. Gao et al. | PubMed | 2025

A review synthesizes evidence concerning intestinal dysbiosis in psoriasis and evaluates probiotics and other microbiome-directed treatments.

| Y. Zhu et al. | PubMed | 2024

A systematic review and meta-analysis evaluates probiotics as adjunctive therapy for psoriasis.

| K. Wei et al. | PubMed | 2024

A systematic review and meta-analysis evaluates probiotic supplementation for psoriasis.

| L. Zeng et al. | PubMed | 2021

A systematic review examines the effectiveness and safety of probiotic supplementation for psoriasis.

Probiotics and Allergic Rhinitis

| X. Luo et al. | PubMed | 2024

A systematic review and meta-analysis evaluates probiotics for preventing and treating allergic rhinitis in children.

| C. Luo et al. | PubMed | 2022

A systematic review and meta-analysis examines the effectiveness and safety of probiotics for allergic rhinitis.

| S. Yan et al. | PubMed | 2022

A systematic review and meta-analysis evaluates probiotics for allergic rhinitis.

| K. Farahmandi et al. | PubMed | 2022

A strain-specific systematic review evaluates probiotics for allergic rhinitis.

| A. E. Zajac et al. | PubMed | 2015

A systematic review and meta-analysis evaluates probiotics in allergic rhinitis.

Probiotics and Pediatric Asthma

| D. Fan et al. | PubMed | 2025

A systematic review evaluates probiotics, prebiotics, synbiotics, and postbiotics for pediatric asthma.

Probiotics and COVID-19

| C. H. H. Chau et al. | PubMed | 2025

A systematic review and meta-analysis evaluates probiotics for prevention and treatment of COVID-19.

| N. T. Iqbal et al. | PubMed | 2025

A review examines persistent intestinal dysbiosis associated with COVID-19 and post-COVID conditions.

| T. Amrouche et al. | PubMed | 2025

A review examines probiotic and prebiotic interventions in respiratory and viral infections.

Probiotics and Multiple Sclerosis

| Z. Zangeneh et al. | PubMed | 2025

A systematic review and meta-analysis examines probiotics in multiple sclerosis using both clinical and experimental studies.

Probiotics and Systemic Lupus Erythematosus

| L. Jin et al. | PubMed | 2025

A review explores intestinal microbiota alterations in systemic lupus erythematosus.

| Rachael Chaeh-Wen Goh et al. | PubMed | 2025

A systematic review evaluates probiotic therapy in experimental models of systemic lupus erythematosus.

Probiotics, Osteoporosis, and Bone Health

| J. N. Harini et al. | PubMed | 2025

A systematic review evaluates probiotic supplementation and bone mineral density.

| A. Ticinesi et al. | PubMed | 2025

A review examines the relationship between intestinal microbiota and bone health.

| F. Wang et al. | PubMed | 2024

A systematic review and meta-analysis examines probiotic supplementation and bone health in postmenopausal women.

Probiotics and Celiac Disease

| T. C. Scherer et al. | PubMed | 2025

A review examines mechanisms through which probiotic bifidobacteria may affect responses to gluten-derived peptides.

| F. Valitutti et al. | PubMed | 2025

A review examines intestinal microbiota in celiac disease and the possibility of personalized microbiome-directed treatment.

Probiotics and Menopausal Health

| R. A. F. Andrews et al. | PubMed | 2025

A systematic review and meta-analysis evaluates probiotics in peri- and postmenopausal women.

Probiotics and Irritable Bowel Syndrome

| B. A. Almabruk et al. | PubMed | 2024

A systematic review and meta-analysis evaluates probiotics for irritable bowel syndrome, including abdominal symptoms and quality of life.

| A. Manandhar et al. | PubMed | 2024

A systematic review examines probiotic treatment in adults with irritable bowel syndrome and inflammatory bowel disease.

| Y. Wu et al. | PubMed | 2024

A network meta-analysis compares probiotics, prebiotics, synbiotics, and fecal microbiota transplantation for IBS.

| R. Yang et al. | PubMed | 2024

A meta-analysis of 20 studies involving more than 3,000 patients evaluates the efficacy and safety of probiotics in IBS.

| V. C. Goodoory et al. | PubMed | 2023

A large systematic review and meta-analysis evaluates individual probiotic strains and combinations for IBS.

| B. Li et al. | PubMed | 2020

A systematic review and meta-analysis assesses the efficacy and safety of probiotics for IBS.

| J. R. Sun et al. | PubMed | 2020

A meta-analysis examines probiotic combinations, species, and strains used for IBS.

Probiotics and Recurrent Urinary Tract Infections

| Z. Han et al. | PubMed | 2025

A network meta-analysis evaluates non-antibiotic strategies for preventing urinary tract infections.

| M. Daniel et al. | PubMed | 2024

A double-blind randomized controlled trial evaluates Lactobacillus rhamnosus PL1 and Lactobacillus plantarum PM1 for preventing recurrent urinary tract infections in children.

| E. J. Nelwan et al. | PubMed | 2024

A meta-analysis evaluates probiotics as adjunctive treatments for several infectious diseases.

| V. Gupta et al. | PubMed | 2024

A randomized controlled study examines oral and vaginal probiotic prophylaxis for recurrent urinary tract infections in women.

| F. J. New et al. | PubMed | 2022

A systematic review evaluates probiotics for recurrent urinary tract infections.

| T. Akgül and B. Karakan | PubMed | 2018

A review examines the relationship between vaginal and urinary microbiota and recurrent urinary tract infection.

Probiotics and Migraine

| O. Grodzka et al. | PubMed | 2025

A clinical review examines the gut microbiota, gut-brain axis, and migraine.

| M. K. Talandashti et al. | PubMed | 2025

A systematic review and meta-analysis compares several dietary supplements used for migraine prevention.

| S. A. Tirani et al. | PubMed | 2024

A randomized clinical trial examines combined probiotic and vitamin D supplementation in people with migraine.

| H. Bazmamoum et al. | PubMed | 2024

A clinical study evaluates probiotics as an adjunct to standard migraine treatment in children.

Probiotics and Rheumatoid Arthritis

| K. Van den Bruel et al. | PubMed | 2025

A systematic review examines diets, dietary supplements, and probiotics in rheumatoid arthritis and related inflammatory disorders.

| X. E. Cheng et al. | PubMed | 2025

A systematic review evaluates nutritional supplements and dietary interventions for rheumatoid arthritis.

| W. Li et al. | PubMed | 2024

An overview of systematic reviews and meta-analyses assesses the quality of evidence supporting probiotics for rheumatoid arthritis.

| Y. Yang et al. | PubMed | 2024

A review explores the intestinal microbiome in rheumatoid arthritis and discusses probiotic treatment.

| H. C. Blenkinsopp et al. | PubMed | 2024

A review examines intestinal permeability, microbial imbalance, and rheumatoid arthritis.

| J. R. Lowe et al. | PubMed | 2020

A systematic review evaluates formulation-specific probiotic effects in inflammatory arthritis.

Probiotics and Chronic Kidney Disease

| S. Wakino et al. | PubMed | 2025

A review examines the kidney-gut axis in chronic kidney disease and microbiome-directed treatment strategies.

| K. Tsuji et al. | PubMed | 2024

A review examines the gut-kidney axis and how intestinal dysbiosis may influence chronic kidney disease.

| J. Ruszkowski et al. | PubMed | 2024

A systematic review and meta-analysis evaluates probiotic and synbiotic supplementation in chronic kidney disease.

| N. Stepanova et al. | PubMed | 2024

A review focuses on probiotic interventions among people receiving peritoneal dialysis.

| C. Liu et al. | PubMed | 2024

A systematic review and meta-analysis assesses probiotics and synbiotics in patients with chronic kidney disease.

| A. Ramezani and D. S. Raj | PubMed | 2014

A foundational review explores alterations of the intestinal microbiome in chronic kidney disease.

Probiotics and Periodontal Disease

| C. Mendonça et al. | PubMed | 2025

An umbrella review examines 30 systematic reviews concerning probiotics for periodontal and peri-implant diseases.

| N. S. Abdul et al. | PubMed | 2024

A systematic review investigates probiotics for prevention and treatment of periodontal disease.

| H. Sharma et al. | Indian Journal of Dental Research | 2024

An overview of 22 systematic reviews and meta-analyses examines probiotic supplementation for periodontal disease.

| H. Doucette et al. | PubMed | 2024

A review examines how prebiotics and probiotics may affect the oral microbiome.

| Carlota Duarte de Mendonça et al. | BMC Oral Health | 2024

A systematic review and network meta-analysis evaluates probiotics added to professional mechanical plaque removal for periodontitis.

| J. Ram et al. | PubMed | 2024

A systematic review examines Lactobacillus reuteri as an adjunct to scaling and root planing in chronic periodontitis.

| L. Puzhankara et al. | Oral Diseases | 2024

A systematic review compares probiotics with antibiotics for managing gingivitis and periodontitis.

Probiotics, Autoimmune Disease, and Inflammation

| Researchers | PubMed | 2026

A systematic review and meta-analysis examines oral probiotic and synbiotic supplementation across autoimmune diseases.

| X. Wang et al. | PubMed | 2024

A review examines the emerging relationship between intestinal microbiota and autoimmune disease.

| L. Zeng et al. | PubMed | 2024

A systematic review and meta-analysis evaluates gut microbiota-based therapies across autoimmune diseases.

Probiotics and Kidney Stones

| H. Taheri et al. | PubMed | 2024

A review examines probiotics and herbal interventions for kidney stones and nephrolithiasis.

Probiotics and Atopic Dermatitis

| Researchers | PubMed / Springer | 2026

An umbrella review evaluates systematic reviews and meta-analyses examining probiotics for atopic dermatitis and related allergic conditions in infants and children.

| Researchers | Journal of Allergy and Clinical Immunology: Global | 2026

A systematic review and meta-analysis examines randomized trials of probiotics for eczema and atopic dermatitis in children and adolescents.

| Researchers | Indian Journal of Dermatology | 2025

A systematic review and meta-analysis examines probiotic supplementation for adults with atopic dermatitis.

| Researchers | PubMed | 2023

A systematic review and meta-analysis evaluates probiotic supplementation in adults with atopic dermatitis.

| Researchers | Pediatric Allergy and Immunology | 2020

A network meta-analysis compares different probiotic strains used to treat pediatric atopic dermatitis.

Probiotics and Helicobacter pylori

| Researchers | Microbial Pathogenesis | 2026

A meta-analysis of 28 randomized controlled trials evaluates probiotic monotherapy for reducing Helicobacter pylori colonization without antibiotics.

Probiotics and Oral Health

| Researchers | Frontiers in Oral Health | 2026

An umbrella review of meta-analyses examines probiotic interventions for dental and oral health.

| Researchers | PubMed | 2025

A systematic review evaluates randomized clinical trials investigating probiotics for enamel demineralization and cariogenic bacteria.