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Awaiting clinical review. This entry is sourced but has not yet been signed off by a pharmacist or clinician.

Live bacteria (Lactobacillus species)

Probiotics (Lactobacillus)

Some Lactobacillus probiotics reduce the chance of diarrhoea while you are taking antibiotics, and Cochrane reviews rate that evidence as low to moderate certainty. The effect belongs to particular strains and conditions rather than to 'probiotics' as a group: it is weak or absent for acute gastroenteritis in children, uncertain for irritable bowel syndrome, and limited to L. reuteri DSM 17938 in breastfed infants for colic. They are well tolerated in healthy people, but the risk of serious infection is higher in people who are severely ill or immunocompromised, or who have a central venous catheter.

Updated
29 September 2026
Plain capsules beside a bowl of natural yoghurt
At a glance
Last reviewed 29 September 2026
Evidence
Moderate
Best for
Antibiotic-associated diarrhoea
Typical form & use
Capsule/sachet, ≥5 billion CFU daily
Onset
2 weeks
Safety
Avoid if immunocompromised or with a central line. 1 known interaction, most serious with immunosuppressants.
Check with your medications →

What it's used for

Evidence is rated per use. The same ingredient can be strong for one thing and traditional for another.

UseEvidenceWhat the research shows
Preventing antibiotic-associated diarrhoeaModerateCochrane's 2025 update (40 trials, 13,419 people, any probiotic) found diarrhoea in 23% on probiotics against 27.4% on control (RR 0.67, 95% CI 0.57 to 0.78), low-certainty evidence. In children, a 2019 Cochrane review of 33 trials found 8% against 19% (RR 0.45), and benefit was clear at doses of 5 billion CFU a day or more; the authors named Lactobacillus rhamnosus and Saccharomyces boulardii as the high-dose examples needing confirmation. Trials used many different strains, so the result cannot be assigned to one Lactobacillus product. NCCIH notes a benefit has not been shown in people aged 65 and over, possibly because few were studied.1,2,8
Preventing C. difficile diarrhoeaModerateIn 38 trials (13,179 people) probiotics cut C. difficile-associated diarrhoea from 3.2% to 1.6% (RR 0.50, 95% CI 0.38 to 0.64), low-certainty evidence; about 65 people need to take one for one case to be prevented. It did not significantly reduce symptomless C. difficile in stool. The review says short-term use is likely safe in people who are not immunocompromised, and most trials were in hospital patients.1,8
Infant colic (L. reuteri DSM 17938)LimitedAn individual-patient meta-analysis of four placebo-controlled trials (345 infants) found L. reuteri DSM 17938 cut crying or fussing by 25 minutes a day more than placebo at day 21 (95% CI 3.5 to 47.3), with success about 1.7 times as likely. The effect was marked in breastfed infants (number needed to treat 2.6) and not significant in formula-fed infants. Results across trials conflict: the largest community trial, in 167 infants, found no benefit and slightly more crying and fussing on the probiotic. This applies to that strain only.5,6,8
Irritable bowel syndromeLimitedA 2014 meta-analysis of 43 trials found probiotics as a group lowered the risk of persisting IBS symptoms (RR 0.79, 95% CI 0.70 to 0.89), but the authors could not say which species or strains work. NCCIH, summarising a later 2018 review of 53 studies, says definite conclusions on effectiveness and best strains were not possible. Trials mixed many organisms, so this is not specific evidence for Lactobacillus.7,8
Acute gastroenteritis in childrenLimitedThe evidence is mostly null. The 2020 Cochrane review (82 trials) found that in low-risk-of-bias studies probiotics made no difference to diarrhoea lasting 48 hours or more (RR 1.00, 95% CI 0.91 to 1.09), and the subgroups for L. rhamnosus GG and S. boulardii were similar. A 971-child US and Canadian trial of L. rhamnosus GG found no difference in moderate-to-severe illness (11.8% against 12.6%) or diarrhoea duration (about 50 hours in both groups). Trials of L. reuteri were consistent but at risk of bias. Not a reason to use probiotics for a child's diarrhoea.3,4

How much

Ranges below are what studies used and what supplements commonly contain. They are not a recommendation for you. Start at the low end.

Antibiotic-associated diarrhoea (children)
≥5 billion CFU a day2
In the 2019 Cochrane review, high-dose trials (5 billion CFU a day or more) showed a stronger effect than low-dose trials. This is a subgroup finding in children; the review says it needs confirming in a large trial.
L. rhamnosus GG in gastroenteritis trial
10 billion CFU, twice daily for 5 days4
The dose used in the 971-child trial, which found no benefit. Shown so you can see that a large dose did not rescue the result.
L. reuteri DSM 17938 for colic
100 million CFU daily6,5
The dose in the 2014 community trial (1 × 10^8 CFU daily for one month). The individual-patient meta-analysis pooled four trials; we did not extract each trial's dose.
Duration
During the antibiotic course2,8
Trials gave probiotics alongside antibiotics, with follow-up of 5 days to 12 weeks in the children's review. NCCIH says the best duration and dose are uncertain.
Timing · No source we read gave a time of day. In the antibiotic trials, probiotics were given alongside the antibiotic course. NCCIH says the best length of treatment is uncertain.With food? · No source we read gave food guidance.How long to trial · For antibiotic-associated diarrhoea, judge it over the antibiotic course itself. For colic, the meta-analysis measured success at day 21. For IBS, no source we read gave a trial length.

How people take it

Capsule or sachet with a named strainFollow the strain-specific dose on the labelChoose a product listing the exact strain (for example L. rhamnosus GG or L. reuteri DSM 17938), since results do not transfer between strains. NCCIH stresses that one Lactobacillus helping does not mean another will.
Drops for infantsStrain and dose per label; ask a doctor firstThe colic evidence is for L. reuteri DSM 17938, mainly in breastfed infants. Give to a young infant only on medical advice.
Yoghurt and fermented foodsNot standardisedNCCIH lists them as a source of probiotic organisms, but the trials above used defined products, not food.

Safety

Who should avoid
  • Premature infants — severe and fatal infections reported; FDA has warned clinicians
  • Severely ill or immunocompromised people — higher risk of harmful effects
  • Central venous catheter or bacterial/fungal translocation risk — serious events reported
  • Very frail or weak hospital patients — Cochrane's safety finding excludes them
  • Young infants — only on medical advice
  • Pregnancy and breastfeeding — safety not assessed in the sources we read; ask first
Known interactions
CautionImmunosuppressants — NCCIH says the risk of harm from probiotics is greater in people with compromised immune systems, so anyone taking immune-suppressing medication should ask their prescriber first.

Questions people ask

Do probiotics stop diarrhoea from antibiotics?

They can lower the chance. Cochrane found diarrhoea in 23% of adults and children on probiotics against 27.4% without (low-certainty evidence), and in children a stronger effect at 5 billion CFU or more a day. The trials used many different strains, so it is not settled which Lactobacillus product works best.

Which strain should I choose?

Choose the strain with evidence for your problem. L. reuteri DSM 17938 has the colic evidence, mainly in breastfed babies, and L. rhamnosus GG was tested in children with antibiotic diarrhoea and gastroenteritis, where it did not help for gastroenteritis. A generic 'Lactobacillus' label tells you little.

Can probiotics help my child's stomach bug?

Probably not. The 2020 Cochrane review found little or no difference in diarrhoea lasting 48 hours or more, and a large trial of L. rhamnosus GG in 971 children found no benefit. No serious adverse events were attributed to probiotics in the Cochrane review.

Are probiotics safe for everyone?

Not everyone. They are generally well tolerated in healthy people, but NCCIH says the risk of harm is greater with severe illness or a weakened immune system, and severe or fatal infections have been reported in premature infants. Serious events in debilitated or immunocompromised children have been linked to central venous catheters.

Sources

  1. Systematic review (Cochrane) Esmaeilinezhad Z, Ghosh NR, Walsh CM, et al. Probiotics for the prevention of Clostridioides difficile-associated diarrhea in adults and children. Cochrane Database Syst Rev. 2025.
  2. Systematic review (Cochrane) Guo Q, Goldenberg JZ, Humphrey C, El Dib R, Johnston BC. Probiotics for the prevention of pediatric antibiotic-associated diarrhea. Cochrane Database Syst Rev. 2019.
  3. Systematic review (Cochrane) Collinson S, Deans A, Padua-Zamora A, et al. Probiotics for treating acute infectious diarrhoea. Cochrane Database Syst Rev. 2020.
  4. RCT Schnadower D, Tarr PI, Casper TC, et al. Lactobacillus rhamnosus GG versus placebo for acute gastroenteritis in children. N Engl J Med. 2018.
  5. Meta-analysis Sung V, D'Amico F, Cabana MD, et al. Lactobacillus reuteri to treat infant colic: a meta-analysis. Pediatrics. 2018.
  6. RCT Sung V, Hiscock H, Tang ML, et al. Treating infant colic with the probiotic Lactobacillus reuteri: double blind, placebo controlled randomised trial. BMJ. 2014.
  7. Meta-analysis Ford AC, Quigley EM, Lacy BE, et al. Efficacy of prebiotics, probiotics, and synbiotics in irritable bowel syndrome and chronic idiopathic constipation: systematic review and meta-analysis. Am J Gastroenterol. 2014.
  8. Regulator/health agency NCCIH. Probiotics: Usefulness and Safety. National Center for Complementary and Integrative Health.

Last reviewed 29 September 2026 · Next review March 2027 · How we rate evidence