Lactobacillus fermentum
Also called Limosilactobacillus fermentum, L. fermentum, CECT5716, Lc40, PCC, VRI-003.
Best grade C across 7 graded outcomes Other Last checked
The short answer
From 13 sourcesL. fermentum results are strain-specific. Breast-milk strain CECT5716 outperformed antibiotics for lactational mastitis in a 352-woman, three-arm trial; in formula it roughly halved gut infections across three trials, but a 460-infant trial found no drop in diarrhoea. Strain PCC cut respiratory illness days in 20 elite runners, and two Korean strains trimmed body fat.
Every graded outcome on this page
7 rows · line = participants- CGrade CGut infections in formula-fed infantsInfant infectionsn 435
- CGrade CInfectious mastitis during breastfeedingMastitisn 352
- CGrade CBody fat in adults with overweight or obesityBody fatn 100
- CGrade CGut and respiratory illness in competitive cyclistsColdsn 99
- CGrade CSleep quality in adults with poor sleepSleepn 84
- DGrade DRespiratory illness in elite distance runnersColdsn 20
- ∅No effectInfectious diarrhoea in formula-fed infantsInfant infectionsn 460
- 4 more graded outcomes, in the evidence chapter
Key facts
- Mastitis (CECT5716)
- 1 billion CFU a day for 3 weeks lowered breast-milk bacterial counts and recurrence vs antibiotics in women with mastitis3
- Infant gut infections
- Formula with CECT5716: incidence rate ratio 0.52 across 3 RCTs and 435 infants; a 460-infant synbiotic formula trial found no difference in infectious diarrhoea411
- Athletes (PCC)
- Respiratory symptom days fell from 72 to 30 in 20 elite distance runners over 4 months of winter training5
- Body fat (MG4231 + MG4244)
- Fat mass fell 1.17 kg vs 0.38 kg on placebo over 12 weeks in 100 adults with overweight7
What it is
Lactobacillus fermentum (now Limosilactobacillus fermentum) is a lactic acid bacterium; trials test named strains such as CECT5716 and PCC.
Forms, side by side
3 forms named in our sources. The rest show what our data holds, and say plainly where it holds nothing yet.
Lactobacillus fermentum forms compared
3 forms| 3 forms | Live-bacteria capsules (CECT5716, PCC, MG4231/MG4244) | Infant formula with CECT5716 | Heat-killed cells (PS150) |
|---|---|---|---|
| Absorption in people | Not absorbed; CECT5716 was recovered from the breast milk of women who took it.3 | Not absorbed; acts in the gut.4 | Not colonising; non-living cells.8 |
| GI tolerance | Safety profile matched placebo in the 12-week body-fat trial; mild gut symptoms were more common with PCC in cyclists.76 | Formula studies were designed as safety trials in healthy infants.4 | No safety concerns are named in the abstract.8 |
| Studied for | Mastitis, colds, body fat | Infant gut infections | Sleep |
- Live-bacteria capsules (CECT5716, PCC, MG4231/MG4244)
- Infant formula with CECT5716
- Heat-killed cells (PS150)
What the human research says
Human trials only, one row per outcome. The form line shows what each trial actually tested. Grades follow our evidence-grading policy.
Trial map
7 graded outcomes, largest study first7 graded outcomes: 4 improved, 1 mixed, 2 no effect. The largest, a 2024 randomized trial of 460 people on infectious diarrhoea in formula-fed infants, found no effect.
1Infectious diarrhoea in formula-fed infants
No effect · No-effect grade · RCT, 460 people, 2024
Healthy 1-month-old formula-fed infants in France, followed to 12 months
Dose, result and source| Outcome | Found | People | Study | Who was studied |
|---|---|---|---|---|
| Infectious diarrhoea in formula-fed infants | No effect | 460 | No-effect grade · RCT, 2024 | Healthy 1-month-old formula-fed infants in France, followed to 12 months |
| Gut infections in formula-fed infants | Improved | 435 | Grade C · Meta-analysis, 2021 | Infants up to 12 months in 3 RCTs |
| Infectious mastitis during breastfeeding | Improved | 352 | Grade C · RCT, 2010 | Breastfeeding women with infectious mastitis (124 L. fermentum, 127 L. salivarius, 101 antibiotics) |
| Body fat in adults with overweight or obesity | Improved | 100 | Grade C · RCT, 2022 | Korean adults aged 19-65 with BMI 25-31.9 |
| Gut and respiratory illness in competitive cyclists | Mixed | 99 | Grade C · RCT, 2011 | Competitive cyclists (64 men, 35 women) |
| Sleep quality in adults with poor sleep | No effect | 84 | Grade C · RCT, 2025 | Adults aged 20-60 with PSQI 5 or more and ISI under 22 |
| Respiratory illness in elite distance runners | Improved | 20 | Grade D · Crossover RCT, 2010 | Healthy elite male distance runners in winter training |
Every graded row
7 rowsShowing 7 of 7 outcomes. Human trials only.
CGrade CGut infections in formula-fed infantsInfant infectionsFewer gut infectionsMeta-analysis
n 435 · 2021
Improved Gut infection incidence was about halved (IRR 0.52, 95% CI 0.36-0.74); heterogeneity was moderate (I2 54.5%).
- Design
- Meta-analysis, n = 435, 2021
- Population
- Infants up to 12 months in 3 RCTs
- Form
- Infant formula with L. fermentum CECT5716 vs placebo formula
- Dose
- About 0.84-1 billion CFU a day
- Duration
- Up to 12 months
- Source
- Reference 4 · PubMed 34208893 (opens PubMed)
CGrade CInfectious mastitis during breastfeedingMastitisBetter than antibiotics on counts and recurrenceRCT
n 352 · 2010
Improved By day 21 milk bacterial counts were lower in both probiotic groups than with antibiotics (2.61 vs 3.28 log10 CFU/mL), and women on probiotics improved more and had fewer recurrences.
- Design
- RCT, n = 352, 2010
- Population
- Breastfeeding women with infectious mastitis (124 L. fermentum, 127 L. salivarius, 101 antibiotics)
- Form
- L. fermentum CECT5716 vs L. salivarius CECT5713 vs prescribed antibiotics
- Dose
- About 1 billion CFU a day (9 log10)
- Duration
- 3 weeks
- Source
- Reference 3 · PubMed 20455694 (opens PubMed)
CGrade CBody fat in adults with overweight or obesityBody fatSlightly more fat lossRCT
n 100 · 2022
Improved DEXA fat mass fell 1,167 g vs 382 g (p = 0.024), body fat 0.85% vs 0.11%, and weight 2.06 vs 1.22 kg; safety did not differ from placebo.
- Design
- RCT, n = 100, 2022
- Population
- Korean adults aged 19-65 with BMI 25-31.9
- Form
- MED-02: L. fermentum MG4231 + MG4244 vs placebo
- Dose
- 5 billion CFU a day
- Duration
- 12 weeks
- Source
- Reference 7 · PubMed 36079841 (opens PubMed)
CGrade CGut and respiratory illness in competitive cyclistsColdsMixed by sexRCT
n 99 · 2011
Mixed Men had less severe gut illness and a lower lower-respiratory symptom load, but mild gut symptoms were about twice as common on the probiotic, and in women respiratory load rose; effects on colds were too uncertain to call.
- Design
- RCT, n = 99, 2011
- Population
- Competitive cyclists (64 men, 35 women)
- Form
- L. fermentum PCC vs placebo
- Dose
- At least 1 billion CFU a day
- Duration
- 11 weeks
- Source
- Reference 6 · PubMed 21477383 (opens PubMed)
CGrade CSleep quality in adults with poor sleepSleepNo overall differenceRCT
n 84 · 2025
No effect PSQI and insomnia scores improved in both groups with no group-by-time difference; a post hoc subgroup with worse insomnia did better on PS150.
- Design
- RCT, n = 84, 2025
- Population
- Adults aged 20-60 with PSQI 5 or more and ISI under 22
- Form
- Heat-killed L. fermentum PS150 vs placebo
- Dose
- Daily (amount in the paper)
- Duration
- 8 weeks
- Source
- Reference 8 · PubMed 41515133 (opens PubMed)
DGrade DRespiratory illness in elite distance runnersColdsFewer sick daysCrossover RCT
n 20 · 2010
Improved Respiratory symptom days were 30 on PCC vs 72 on placebo (p < 0.001), with a trend to milder illness; salivary IgA and running performance did not change.
- Design
- Crossover RCT, n = 20, 2010
- Population
- Healthy elite male distance runners in winter training
- Form
- L. fermentum VRI-003 (PCC) capsules vs placebo
- Dose
- 12.6 billion CFU a day
- Duration
- 4 months (crossover)
- Source
- Reference 5 · PubMed 18272539 (opens PubMed)
∅No effectInfectious diarrhoea in formula-fed infantsInfant infectionsNo fewer gut infectionsRCT
n 460 · 2024
No effect Infectious diarrhoea rates in the first year did not differ (0.56 vs 0.60 episodes per infant-year). Lower respiratory tract infections, a secondary outcome, were less frequent (0.79 vs 1.01; rate ratio 0.77, 95% CI 0.60-1.00).
- Design
- RCT, n = 460, 2024
- Population
- Healthy 1-month-old formula-fed infants in France, followed to 12 months
- Form
- Synbiotic infant and follow-on formula with galacto-oligosaccharides plus L. fermentum CECT5716 vs standard formula
- Dose
- In formula (amount not stated in the abstract)
- Duration
- Until 12 months of age
- Source
- Reference 11 · PubMed 38462218 (opens PubMed)
What the numbers add up to
Each point is worked out from the data and the sources numbered on this page, with the arithmetic shown under it. It adds no new data and is not medical advice.
Studied doses
Doses used in research, shown against the official limits. They describe the studies, not a recommendation for you.
Studied doses in research, not advice. These are amounts used in research, not personal advice. Your clinician or pharmacist can say what fits you.
Doses studied in human trials
Interactions and safety
Published interactions only: each row cites a source. No row means none was found in our sources, not that a combination is safe.
What Lactobacillus fermentum meets
2 cited rowsMedicines 2
Supplements and foods 0
No supplement rows in our sources.
- Drug label or FDA notice
Choose a medicine or supplement above to read its cited rows here.
Also cited:
Antibiotics
Drug labelDrug label or FDA notice
Antibiotics, for example any oral antibiotic course: Health Canada's probiotics monograph directs that bacterial probiotics be used at least 2–3 hours before or after antibiotics.
Source 1, Health Canada, Natural and Non-prescription Health Products Directorate (2026)
Immunosuppressive treatment
Drug labelDrug label or FDA notice
Immunosuppressive treatment, for example long-term corticosteroids: Health Canada lists an immune-compromised condition, including long-term corticosteroid treatment, as a contraindication for probiotics; NCCIH and ODS say harmful effects are more likely in people with compromised immune systems.
Source 1, Health Canada, Natural and Non-prescription Health Products Directorate (2026); Source 2, National Center for Complementary and Integrative Health (NCCIH) (2019); Source 12, NIH Office of Dietary Supplements (2025)
Interactions
2 agents| Agent | What the source says | Evidence |
|---|---|---|
| Medicines2 | ||
| Antibioticse.g. any oral antibiotic course | Health Canada's probiotics monograph directs that bacterial probiotics be used at least 2–3 hours before or after antibiotics.1 | Drug label |
| Immunosuppressive treatmente.g. long-term corticosteroids | Health Canada lists an immune-compromised condition, including long-term corticosteroid treatment, as a contraindication for probiotics; NCCIH and ODS say harmful effects are more likely in people with compromised immune systems.1212 | Drug label |
Check with what you take
Kept on this device onlyAdd what you take. We list every interaction our evidence profiles cite between Lactobacillus fermentum and your picks, and between your picks.
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Add a supplement or medicine you take to check it against Lactobacillus fermentum.
Starting from one medicine? The interaction checker rates how serious each pair is, on a curated list of 19 entries for 11 medicines. This cabinet has no severity rating: it lists every interaction row our supplement pages cite.
Who should be careful
5 groups- Immune-compromised conditions
- Health Canada's probiotic monograph: do not use if you have an immune-compromised condition (for example AIDS, lymphoma, or long-term corticosteroid treatment).1
- Fever or severe gut symptoms
- Health Canada: ask a health care practitioner before use if you have fever, vomiting, bloody diarrhoea or severe abdominal pain.1
- Premature infants and seriously ill people
- NCCIH reports severe or fatal infections in premature infants given probiotics, which FDA warned health care providers about in 2023, and higher risk in people with serious illness.213
- Central lines and intensive care
- Lactobacillus bloodstream infection is rare, but risk factors include severe illness, immune suppression, ICU admission and central venous catheters. In ICU patients given probiotics, bacteria in the blood were genetically matched to the capsule strain.910
- Pregnancy and breastfeeding
- The NCCIH and NIH ODS probiotic fact sheets give no pregnancy- or breastfeeding-specific safety data for probiotic supplements; NCCIH advises consulting a health care provider before using one. In a mastitis trial, breastfeeding women used CECT5716 for 3 weeks and the strain was later found in their milk; the abstract reports no side-effect data.2123
How to read the label
What to check on the Supplement Facts panel.
Frequently asked questions
Short answers to common questions; the numbers link to the sources below.
Common questions
7 answersDoes L. fermentum help with mastitis?
In 352 breastfeeding women with infectious mastitis, 3 weeks of CECT5716 lowered milk bacterial counts and recurrence more than antibiotics did. There was no placebo group.3
Does it help athletes avoid colds?
Does L. fermentum help weight loss or sleep?
Is L. fermentum safe?
Can it be used with antibiotics?
Is it used in infant formula?
Sources
13 sources: trial abstracts, NIH fact sheets and reference databases. Numbers in the text link here.
Sources cited on this page
13 sources- 1Probiotics (Natural Health Product monograph, April 24, 2026)Guideline Health Canada, Natural and Non-prescription Health Products Directorate, 2026 · webprod.hc-sc.gc.ca
- 2Probiotics: Usefulness and SafetyFact sheet National Center for Complementary and Integrative Health (NCCIH), 2019 · nccih.nih.gov
- 3Treatment of infectious mastitis during lactation: antibiotics versus oral administration of Lactobacilli isolated from breast milk.RCT Clin Infect Dis, 2010 · PMID 20455694
- 4Evaluation of the Effect of Limosilactobacillus fermentum CECT5716 on Gastrointestinal Infections in Infants: A Systematic Review and Meta-Analysis.Meta-analysis Microorganisms, 2021 · PMID 34208893
- 5Oral administration of the probiotic Lactobacillus fermentum VRI-003 and mucosal immunity in endurance athletes.Crossover RCT Br J Sports Med, 2010 · PMID 18272539
- 6Lactobacillus fermentum (PCC®) supplementation and gastrointestinal and respiratory-tract illness symptoms: a randomised control trial in athletes.RCT Nutr J, 2011 · PMID 21477383
- 7Effect of MED-02 Containing Two Probiotic Strains, Limosilactobacillus fermentum MG4231 and MG4244, on Body Fat Reduction in Overweight or Obese Subjects: A Randomized, Multicenter, Double-Blind, Placebo-Controlled Study.RCT Nutrients, 2022 · PMID 36079841
- 8Heat-Treated Limosilactobacillus fermentum PS150 Improves Sleep Quality with Severity-Dependent Benefits: A Randomized, Placebo-Controlled Trial.RCT Nutrients, 2025 · PMID 41515133
- 9Lactobacillus Bacteremia and Probiotics: A Review.Review Microorganisms, 2023 · PMID 37110319
- 10Genomic and epidemiological evidence of bacterial transmission from probiotic capsule to blood in ICU patients.Observational Nat Med, 2019 · PMID 31700189
- 11Efficacy and safety of a synbiotic infant formula for the prevention of respiratory and gastrointestinal infections: a randomized controlled trial.RCT Am J Clin Nutr, 2024 · PMID 38462218
- 12Probiotics: Fact Sheet for Health Professionals (updated March 25, 2025)Fact sheet NIH Office of Dietary Supplements, 2025 · ods.od.nih.gov
- 13Risk of Invasive Disease in Preterm Infants Given Probiotics Formulated to Contain Live Bacteria or YeastSafety communication U.S. Food and Drug Administration, 2023 · fda.gov
What changed
Every dated change to this page: what changed, who made it and why.
Change log
3 entries| Date | Change | Who and why |
|---|---|---|
| evidence, interactions, who should avoid, FAQ, key facts, summary, sources | Added the 2024 GOLF III RCT of a synbiotic formula with CECT5716 (PMID 38462218, null on infectious diarrhoea); added antibiotic-spacing and immunosuppressant interactions from the Health Canada monograph, NCCIH and NIH ODS; added a pregnancy and breastfeeding note (NCCIH, ODS, PMID 20455694); cited the FDA 2023 preterm-infant safety communication; new antibiotics FAQ. Fact-checked against the sources; corrected: the summary no longer implies all 352 mastitis-trial women took CECT5716 (124 did). | Writer: Kymata Health EditorialTrigger: A–Z page audit |
| all | Initial editorial evidence review. Every PMID checked against NCBI E-utilities esummary (title, year, journal) and each cited abstract read; numbers taken from the abstracts. Funding and ties: Biosearch Life employee authors (2021 meta-analysis), MEDIOGEN author affiliations (2022); other abstracts name no funder. Safety rows use Health Canada and NCCIH only. No product listed in this pass. | Writer: Kymata Health EditorialTrigger: new page |
| who should avoid | Safety review: added central venous catheter and ICU bloodstream-infection risk (Microorganisms 2023 review; Nat Med 2019 genomic study) and the FDA 2023 preterm-infant warning noted by NCCIH. | Writer: Kymata Health EditorialTrigger: safety review |
Supplement & Nutrient Encyclopedia. Educational information only; it is not medical advice and does not replace a clinician. Dietary supplements are not intended to diagnose, treat, cure or prevent any disease. Statements about supplements have not been evaluated by the FDA.