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Printed from https://bottledhope.co/supplements/probiotics/. Last reviewed 2026-10-18. Check the site for the latest version.

Probiotics

Live microbes, mostly bacteria and some yeasts, found in some fermented foods and sold as supplements. Studied for diarrhea linked to antibiotics and for IBS.

Explained simply · Last reviewed

What it is

Probiotics are live microorganisms, mostly bacteria but also some yeasts. The NIH Office of Dietary Supplements (ODS) quotes the definition used by an international scientific association: "live microorganisms that, when administered in adequate amounts, confer a health benefit on the host". ODS adds that not every food or supplement labeled "probiotic" has proven health benefits, and that the potential benefits of probiotics are the focus of a great deal of scientific research.

More about Probiotics

The NIH Office of Dietary Supplements (ODS) quotes the definition used by an international scientific association: "live microorganisms that, when administered in adequate amounts, confer a health benefit on the host". ODS adds that not every food or supplement labeled "probiotic" has proven health benefits, and that the potential benefits of probiotics are the focus of a great deal of scientific research.

ODS reports that probiotics are found in some fermented foods, such as yogurt, are added to certain other foods, and are sold as supplements in capsules, powders, liquids and other forms. It notes that many fermented foods with live cultures, such as kimchi, kombucha and sauerkraut, do not typically contain proven probiotic microorganisms. ODS adds that a product can contain a single strain or several.

ODS explains that a probiotic is identified by its genus, its species, and a strain designation, such as the "GG" in Lactobacillus rhamnosus GG. It says some effects are specific to particular strains, so evidence about one strain may not carry over to another, or to probiotics as a whole. This page covers only a few uses where systematic reviews and health authorities have reached a conclusion, and it names the strains that the evidence is about.

Also known as: live cultures, Lactobacillus rhamnosus GG, LGG, Saccharomyces boulardii, Bifidobacterium

At a glance

Safety: known risks and 5 groups who should avoid it or take extra care. See Safety ↓

Claims made about Probiotics, and how strong the evidence is for each:

Each rating follows our published rules and the sources cited for it. We don’t add our own medical judgment. How we rate

Safety

Read this before the ratings below.

Risks

  • NIH ODS says probiotics are unlikely to cause harm in healthy people, and that side effects are usually minor, self-limited digestive symptoms such as gas.
  • ODS reports that probiotic use has been linked to a few cases of bloodstream infection with bacteria (bacteremia) or fungi (fungemia), and to other infections causing severe illness. Most of these cases involved people who were severely ill or immunocompromised. In some cases the probiotic strain was confirmed as the cause; in others it was not.
  • ODS reports that at least 60 reports published since 1966 describe fungemia linked to probiotics containing the yeast Saccharomyces cerevisiae. In many of these cases the patient was in intensive care, was being fed by tube or intravenously, had a central venous catheter, or had received broad-spectrum antimicrobial treatment.
  • ODS reports that in a retrospective analysis of intensive care patients at one Boston hospital, those given LGG, typically through a feeding tube, had a markedly higher risk of Lactobacillus bloodstream infection than patients who were not given it.
  • The FDA warns that preterm infants given probiotics are at risk of invasive, potentially fatal disease caused by the bacteria or yeast the product contains. It reports a preterm infant who was given a probiotic in hospital, developed sepsis caused by Bifidobacterium longum, and died.
  • The FDA has not approved any probiotic product for use as a drug or biological product in infants. It notes that probiotics sold to treat or prevent disease in infants have not been through its premarket review for safety and effectiveness, or been checked against its manufacturing and testing standards, including testing for unwanted organisms.
  • ODS notes that some clinical trials of probiotics were not designed to answer safety questions, which leaves gaps in the safety evidence.
  • A 2026 systematic review looked at 30 studies of prebiotics, probiotics and synbiotics given to adults as an add-on treatment for acute pancreatitis (inflammation of the pancreas). The reviewers report that the most prominent safety signal was a loss of blood supply to the bowel (bowel ischemia). In the largest trial, in patients predicted to have severe acute pancreatitis, it occurred in 9 of 152 patients given a multispecies live probiotic and none of 144 given a placebo, and more patients died in the probiotic group.
  • The same reviewers say that most studies reported acceptable safety and that minor side effects were not consistently more common, but that safety reporting was incomplete: many studies did not report bowel ischemia or bloodstream infections separately. They write that the serious safety concerns rest mainly on the one large trial. They did not grade how certain their findings are.
  • Taking prebiotic, probiotic and synbiotic studies together, the authors of the 2026 review found these products may be linked to fewer infection-related complications and shorter hospital stays, though the hospital-stay results differed widely between studies. They add that evidence for mortality or other severe outcomes "is not robust". They conclude that current evidence does not support routine use of these products in acute pancreatitis, "particularly live probiotic preparations in severe or critically ill patients".

Who should avoid it or take extra care

  • Preterm infants: the FDA warns of invasive, potentially fatal infection from the microbes in probiotic products.
  • People who are severely ill or immunocompromised: ODS reports that most probiotic-linked bloodstream infections involved these groups. It reports that the World Gastroenterology Organisation advises that people with compromised immune function or other serious underlying diseases restrict probiotic use to the strains and uses that have proven efficacy. NCCIH, the US agency that studies complementary medicine, says the risk of harmful effects is greater in people with severe illnesses or compromised immune systems. It says that when probiotics are being considered for high-risk individuals, such as premature infants or seriously ill hospital patients, the potential risks should be carefully weighed against their benefits.
  • People with acute pancreatitis, especially predicted severe disease: the authors of the 2026 review conclude that current evidence does not support routine use of prebiotics, probiotics or synbiotics in acute pancreatitis. They write that it "does not support routine use of multispecies live probiotics in critically ill or predicted severe acute pancreatitis patients".
  • People in intensive care, people with a central venous catheter, and people fed by tube or intravenously: ODS reports that in many of the cases of fungemia linked to probiotics containing the yeast Saccharomyces cerevisiae, the patient had one of these features. The 2019 Cochrane review in children also reports serious adverse events, from observational studies, in severely debilitated or immunocompromised children with risk factors including central venous catheter use.
  • The 2025 Cochrane review on C. difficile limits its conclusion that short-term probiotic use is likely not associated with adverse effects to people taking antibiotics who are not immunocompromised.

Safety sources: Source [1]Source [2]Source [3]Source [4]Source [5]Source [6]

What the evidence says

Each claim is rated on its own evidence. Ratings follow the scale on our methodology page.

  • Prevents diarrhea caused by antibiotics in children (specific strains only; LGG and S. boulardii are the most studied) Evidence rating: Limited

    Parents give it to children taking antibiotics hoping to spare them the diarrhea that antibiotics can bring.

    A 2019 Cochrane review of 33 trials found fewer children on antibiotics got diarrhea with probiotics, rated moderate certainty; it rated how long diarrhea lasted low certainty.

    A 2019 Cochrane review pooled 33 trials in 6,352 children taking antibiotics. Diarrhea developed in 8% of children given a probiotic and 19% of those given a placebo or no treatment. The reviewers rated how sure they could be of this finding (certainty) as moderate. They rated their other outcomes lower. Adverse events and how long diarrhea lasted were low certainty. Effects on the gut microbiome, reported by one trial of 40 children, were very low certainty. In the review, probiotics shortened diarrhea by almost a day, a finding the reviewers rated low certainty.

    The trials in the 2019 review tested 19 different probiotic interventions from several groups of bacteria and yeasts, alone or in combination. A subgroup analysis found no difference between species, while higher-dose products worked better than lower-dose ones. The reviewers say the benefit of higher-dose probiotics such as Lactobacillus rhamnosus or Saccharomyces boulardii, the most-studied products, still needs confirming in a large trial. They say it is premature to draw firm conclusions about other probiotics.

    In the 2019 review, none of the 24 trials that tracked adverse events reported a serious one caused by probiotics (low-certainty evidence). The reviewers note, though, that observational studies outside the review have reported serious events in severely debilitated or immunocompromised children. Of the 17 trials that reported their funding, 9 (1,627 children) were industry-funded. Industry-funded and independent trials both showed a benefit, with no significant difference between them. The review searched for trials up to May 2018.

    NIH ODS also concludes that LGG or S. boulardii, started within 2 days of the first antibiotic dose, helps reduce the risk in children. A 2025 Cochrane review focused on C. difficile also found fewer cases of antibiotic-associated diarrhea with probiotics. It pooled adults and children for that outcome and rated it low certainty. This page rates the claim limited because one of the diarrhea outcomes it rests on, how long diarrhea lasted, was rated low certainty.

    Sources: Source [1]Source [2]Source [3]

  • Prevents diarrhea caused by antibiotics in adults aged 18 to 64 (specific strains only; the ODS summary centers on LGG and S. boulardii, though the LGG result in adults was not significant) Evidence rating: Limited

    Adults under 65 on a course of antibiotics take it hoping to avoid the diarrhea that antibiotics can bring.

    NIH ODS says LGG or S. boulardii helps reduce this risk in adults 18 to 64, though LGG was not significant in adults; a 2025 Cochrane review rated its adult-and-child estimate low certainty.

    NIH ODS concludes that starting LGG or Saccharomyces boulardii within 2 days of the first antibiotic dose helps reduce the risk in adults aged 18 to 64. The strains differ in the adult evidence it describes. A meta-analysis of S. boulardii found a lower risk in adults (8.2% against 17.4%). In a meta-analysis of LGG, the reduction was statistically significant only in children, not when the 1,052 adults were analyzed separately. ODS also reports that the reduction has not been seen in adults aged 65 and over, and that there is no evidence of greater benefit from products containing more than one strain.

    The most recent pooled estimate comes from a 2025 Cochrane review focused on C. difficile. Across 40 trials with 13,419 adults and children, antibiotic-associated diarrhea developed in 23% of people given probiotics and 27.4% of controls. The reviewers rated that estimate low certainty. They downgraded it because results differed between trials (heterogeneity), and for suspected publication bias (the chance that trials with less favorable results were never published). That review combined adults and children for this outcome.

    Because the most recent review rates the evidence low, this page rates the claim limited rather than following the more positive ODS summary.

    Sources: Source [1]Source [2]

  • Prevents C. difficile diarrhea in people taking antibiotics (many different strains pooled) Evidence rating: Limited

    People taking antibiotics take it hoping to avoid diarrhea caused by the C. difficile bacterium.

    A 2025 Cochrane review found C. difficile diarrhea in 1.6% of people given probiotics and 3.2% of controls, rated low certainty; in trials at typical risk the gap was not significant.

    A 2025 Cochrane review pooled 38 trials in 13,179 adults and children taking antibiotics. C. difficile-associated diarrhea developed in 1.6% of those given probiotics and 3.2% of controls. The reviewers put this as one case that may be prevented for every 65 people taking probiotics. They rated this low certainty. They downgraded it for indirectness and for imprecision (a limited number of events, and fewer participants than the reviewers calculated they needed), as the summary-of-findings table and discussion of the review set out; the abstract states the reasons only briefly.

    The reviewers' concern about indirectness is how common C. difficile diarrhea was in the control groups. The benefit was larger in trials where more than 5% of the control group developed it, a rate the reviewers call very atypical in real-world patients. Most of the trial data came from trials with a typical control rate below 3%. There the result was not statistically significant (risk ratio 0.92, 95% confidence interval 0.65 to 1.31). The reviewers describe it as suggesting "a very small effect" in one place and as "trivial and unimportant" in another.

    The reviewers consider it "plausible" that this difference between trials "may be a trustworthy subgroup effect". But they say caution is warranted because it rests on comparisons between trials, and that it may be the result of a small-study effect. For C. difficile diarrhea overall, they report that their funnel plot and statistical test were "not suggestive of small-study effects" (P = 0.93).

    The reviewers also noted that the two largest trials did not show a clear benefit. They say this was presumably because those trials were underpowered: only 1.2% and 1.9% of their control groups developed C. difficile diarrhea. They give as an alternative possibility that the typical risk is below 3% for most people prescribed an antibiotic and that most of the small trials are not representative.

    About 30% of the trials in the review had no published protocol or trial registration, and the reviewers judged 28 of the 47 included studies at high risk of other bias, such as author affiliations with, and financial support from, probiotic companies. The trials used many different probiotics without comparing them directly, so the review could not say which works best. The reviewers describe the benefit as small, limit their safety conclusion to people who are not immunocompromised, and call for large placebo-controlled trials in people at low risk of C. difficile.

    Sources: Source [1]

  • Relieves irritable bowel syndrome (IBS) symptoms (effects vary by strain and symptom) Evidence rating: Limited

    People with irritable bowel syndrome take it hoping it will ease their abdominal pain, bloating and other symptoms.

    NIH ODS says probiotics might reduce some IBS symptoms, and that more high-quality trials are needed to confirm which strain, dose and duration work.

    NIH ODS concludes that probiotics might reduce some symptoms of IBS. It says more high-quality trials are needed to confirm which strain, dose, and duration work, and which type of IBS responds. The meta-analyses it summarizes mostly found a modest benefit, but one of them found the underlying studies to be of low quality.

    ODS also reports that which strains help probably depends on the symptom. In one analysis of 10 trials, products containing Bifidobacterium breve, Bifidobacterium longum, or Lactobacillus acidophilus lowered pain scores. Several others in that analysis, including Saccharomyces boulardii, showed no significant effect on pain, and that analysis found no clear positive effect on quality of life.

    On multi-strain products, ODS reports that in one meta-analysis some combinations did better than single strains, though no specific combination did better than another. In a later systematic review of 35 trials, most of the trials that found a reduction in overall symptoms or a meaningful reduction in abdominal pain used multi-strain products. Citing other analyses, ODS adds that only trials of multi-strain products found a clinically meaningful improvement in quality of life.

    Sources: Source [1]

  • Prevents vaginal infections (vulvovaginitis) or preterm birth when taken by mouth during pregnancy (multi-strain blends containing Lactobacillus rhamnosus were studied) Evidence rating: Insufficient

    Pregnant women take it hoping to ward off yeast infections and bacterial vaginosis, and to lower their chance of giving birth early.

    A 2026 review found four trials of oral probiotics in pregnancy; none showed a significant effect on vaginal infections or preterm birth, and it rated that evidence low certainty.

    A 2026 systematic review searched for randomized trials of probiotics taken by mouth by pregnant women, for the prevention of vaginal infections (vulvovaginitis) and preterm birth. It found four: two in Israel, one in Malaysia and one in Brazil. The largest, in Brazil, had 644 women, and the smallest had 40. Every trial used a blend of several bacteria that included a Lactobacillus rhamnosus strain. No trial of a yeast probiotic met the reviewers' criteria.

    The reviewers report that none of the four trials showed a statistically significant effect on vulvovaginitis or preterm birth. They rated certainty low for both outcomes. They give small trials, differences between trials and imprecise estimates as the main reasons. In the Malaysian trial, women given the probiotic after treatment for a yeast infection had fewer Candida yeasts and more Lactobacillus bacteria in vaginal samples. That is a laboratory measure, not a count of infections.

    In the 2024 Israeli trial of 100 women with normal vaginal bacteria, vulvovaginitis was not significantly less common with the probiotic; only itching was significantly rarer (8% against 27%). In the Brazilian trial, the women had asymptomatic bacterial vaginosis or abnormal vaginal bacteria. Among those not at risk of preterm birth who completed treatment without antibiotics, fewer gave birth before 37 weeks with the probiotic, but the difference was not significant (p = 0.06). Among the 35 women at risk of preterm birth, the probiotic group had more preterm births, also not significant.

    The review describes all four trials as placebo-controlled. Its own account of the 2020 Israeli trial, though, describes a crossover in which each group spent two months without treatment rather than on a placebo, and the trial's title calls it open label. The review's highlights say oral probiotics "demonstrated potential effectiveness in reducing vulvovaginal infection recurrence"; its results report no significant effect on vulvovaginitis in any trial. The reviewers conclude that oral probiotics "are not effective as standalone therapy for vulvovaginitis". They suggest vaginal use may work better, while noting it "has yet to be studied in populations of pregnant women". They call for further studies, particularly on preterm birth.

    None of the four trials reported a severe adverse event. The reviewers say only the Brazilian trial noted minor events, such as nausea, diarrhea and uterine contractions, all infrequent and non-severe. They conclude that oral probiotics "appear to be safe during pregnancy" and rate certainty for safety moderate. This page does not read that as showing probiotics are safe in pregnancy: four trials with no severe events are too few to show that harms are absent. This page rates the claim insufficient: no trial found a significant effect, which at low certainty is too little evidence to show an effect either way.

    Sources: Source [1]

How and when to take it

What the cited sources say about taking it. Ask your doctor or pharmacist what applies to you.

  • In the evidence on antibiotic-associated diarrhea, timing mattered

    NIH ODS reports that taking probiotics within 2 days of the first antibiotic dose is more effective than starting them later. Source [1]

  • Check the strain name, and the count at the end of shelf life

    NIH ODS explains that probiotics are identified by strain, and that their effects can be strain-specific. Because probiotics can die during storage, it advises looking for products labeled with the number of colony-forming units (CFU) at the end of shelf life, not at the time of manufacture. It also notes that products with higher counts are not necessarily more effective. Source [1]

  • Follow the storage instructions on the label

    NIH ODS reports that the World Gastroenterology Organisation recommends checking labels for storage conditions: some products need refrigeration and others can be kept at room temperature. Source [1]

Which form the evidence used

Supplements are sold in several forms. This is what the sources on this page say about them — which form the research used, and any comparison those sources themselves made. Where they made none, this page does not rank the forms.

  • Lacticaseibacillus rhamnosus GG (often labeled Lactobacillus rhamnosus GG, or LGG), What the sources supportDetails

    One of the two most-studied probiotics for antibiotic-associated diarrhea. NIH ODS reports that LGG has been shown to reduce the risk of it, and the 2019 Cochrane review in children names it among the most-studied products. In the meta-analysis of LGG that ODS describes, the reduction was statistically significant in children but not when adults were analyzed separately. ODS explains that probiotics are identified by genus, species, and a strain designation, and that effects can be specific to a strain, so the "GG" on the label matters, not only the species name. Source [1]Source [2]

  • Saccharomyces boulardii (a yeast), What the sources supportDetails

    The other most-studied probiotic for antibiotic-associated diarrhea. NIH ODS reports that it has been shown to reduce the risk in both adults and children. The 2019 Cochrane review in children compared species in a subgroup analysis and found no difference between them in preventing this diarrhea, so the sources do not rank it above or below LGG. Source [1]Source [2]

  • Multi-strain blends, What the sources supportDetails

    For antibiotic-associated diarrhea in children, the 2019 Cochrane review found that single-strain and multi-strain products both reduced diarrhea, with no significant difference between them. For antibiotic-associated diarrhea generally, NIH ODS reports no evidence that using more than one strain gives a greater benefit. For IBS, ODS reports that in one systematic review of 35 trials, most of the trials that found a reduction in overall symptoms or a meaningful reduction in abdominal pain used multi-strain products. Citing other analyses, it adds that only trials of multi-strain products found a clinically meaningful improvement in quality of life, and that in one meta-analysis some combinations did better than single strains, though no specific combination did better than another. Source [1]Source [2]

  • Strains and products not tested in research, Details

    NIH ODS notes that the effects of many commercial probiotic products have not been examined in research studies. For antibiotic-associated diarrhea in children, the 2019 Cochrane reviewers say it is premature to draw firm conclusions about probiotics other than the most-studied ones. Source [1]Source [2]

Sources

  1. Probiotics for the prevention of pediatric antibiotic-associated diarrhea
    Cochrane Database of Systematic Reviews, 2019 · Systematic review · Primary source · Certainty: very low
  2. Probiotics for the prevention of Clostridioides difficile-associated diarrhea in adults and children
    Cochrane Database of Systematic Reviews, 2025 · Systematic review · Primary source · Certainty: low
  3. Probiotics: Fact Sheet for Health Professionals
    NIH Office of Dietary Supplements, 2025 · Health authority summary · Primary source
  4. The Role of Probiotics in Primary and Secondary Prevention of Vulvovaginitis during Pregnancy and Preterm Labor: A Systematic Review
    Medical Principles and Practice, 2026 · Systematic review · Primary source · Certainty: low
  5. Risk of Invasive Disease in Preterm Infants Given Probiotics Formulated to Contain Live Bacteria or Yeast
    U.S. Food and Drug Administration, 2023 · Health authority summary · Primary source
  6. Safety and efficacy of microbiota-directed adjunctive therapy in acute pancreatitis: a systematic review and meta-analysis of prebiotics, probiotics, and synbiotics
    Frontiers in Medicine, 2026 · Meta-analysis · Primary source
  7. Probiotics: Usefulness and Safety
    National Center for Complementary and Integrative Health, NIH, 2019 · Health authority summary · Primary source

Page history

Show all 6 changes to this page
  • — Added a claim on preventing vaginal infections and preterm birth with oral probiotics in pregnancy, rated insufficient, from a 2026 systematic review of four trials. No existing rating changed.
  • — Safety section updated for a 2026 systematic review of prebiotics, probiotics and synbiotics in acute pancreatitis: it reports more bowel ischemia and deaths with a multispecies live probiotic in one large trial in predicted severe disease. An NCCIH caution on seriously ill hospital patients was added. No rating changed.
  • — Rewritten to the content style guideline; ratings and sources unchanged.
  • — Source audit: both Cochrane reviews are now read in full. No rating changed. The C. difficile and adult antibiotic-diarrhea summaries now give the 2025 review's reasons for rating each outcome low certainty, and the C. difficile summary reports its result in trials with a typical control rate below 3%.
  • — Published. All four claims, the safety section and every source passed the site's source and wording reviews. The children's antibiotic-diarrhea claim is rated on its lowest diarrhea outcome by owner decision. Open items stay logged in docs/08-open-decisions.md.
  • — First drafted. Narrowed to four uses: antibiotic-associated diarrhea in children rated limited, antibiotic-associated diarrhea in adults rated limited, C. difficile diarrhea rated limited, and IBS symptoms rated limited. The safety section leads on infection risk in preterm infants and in severely ill or immunocompromised people.