Remedy · ferment
Probiotics: where the evidence is real, and where it is not
Live microbes sold as supplements and found in some fermented foods. Trials support specific uses alongside antibiotics; most other claims are unproven, and effects depend on the strain.
By the editors of Alimentotherapy Last reviewed 6 min read Not medical advice
Probiotics
Best-supported use: Antibiotic-associated diarrhea in children
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The short answer
Probiotics have their best evidence alongside antibiotics: in a Cochrane review of 33 trials in children, 8% of those given probiotics developed antibiotic-associated diarrhea versus 19% of controls, and another Cochrane review found moderate-certainty evidence of fewer C. difficile infections Guo 2019; Goldenberg 2017. For most other gut conditions the American Gastroenterological Association recommends probiotics only within clinical trialsSu 2020.
The evidence, use by use
Each claim graded on human studies only. How we grade
| Use | Grade | What the research found |
|---|---|---|
| Antibiotic-associated diarrhea in children | Moderate | Across 33 trials (6,352 children), diarrhea developed in 8% of those given probiotics alongside antibiotics versus 19% of controls (moderate certainty). High doses (5 billion CFU a day or more) worked better than low doses. Guo 2019 |
| C. difficile diarrhea during antibiotic treatment | Moderate | In 31 trials (8,672 adults and children), C. difficile diarrhea occurred in 1.5% on probiotics versus 4.0% on placebo or no treatment. The benefit was seen in trials where baseline risk was above 5%, not in lower-risk groups. Goldenberg 2017; Su 2020 |
| Irritable bowel syndrome | Limited | NCCIH reports that probiotics may help overall IBS symptoms and abdominal pain, but definite conclusions, and which strains work, could not be drawn. The AGA recommends them for IBS only within clinical trials. NCCIH; Su 2020 |
| Fewer upper respiratory infections (colds) | Limited | A Cochrane review of 23 trials (6,950 people) found probiotics may reduce the number of people with at least one upper respiratory infection (risk ratio 0.76) and may shorten episodes by about a day, mostly on low-certainty evidence. Zhao 2022 |
| Acute infectious diarrhea (stomach bugs) | Not supported | A Cochrane review of 82 studies (12,127 participants, mostly children) found probiotics probably make little or no difference to diarrhea lasting 48 hours or more in the low-risk-of-bias trials. The AGA suggests against them for children with acute gastroenteritis. Collinson 2020; Su 2020 |
| Changing the gut microbiome in healthy adults | Not supported | A systematic review of seven placebo-controlled trials in healthy adults found no effect of probiotic supplements on fecal microbiota diversity, richness or evenness; only one trial found a change in overall community structure. Kristensen 2016 |
What counts as a probiotic
Probiotics are live microorganisms, mostly strains of Lactobacillus, Bifidobacterium and the yeast Saccharomyces boulardii, taken in amounts intended to have a benefit. They are sold mostly as dietary supplements. These do not need FDA approval before they are marketed, and some products have been found to contain organisms other than those listed on the label NCCIH.
Effects are tied to the specific strain and dose. NCCIH notes that different probiotics may have different effects and that it is still not known which ones are helpful NCCIH. The AGA guideline, for example, suggests particular products for C. difficile risk during antibiotics: S. boulardii, or specific two-, three- and four-strain Lactobacillus combinations, over other probiotics Su 2020. A result for one product does not carry over to another.
Fermented foods such as yogurt, kefir, sauerkraut and kimchi can contain live microbes, but the trials on this page mostly used defined supplement strains at high doses. Those foods have their own pages: yogurt and kefir and fermented foods.
With antibiotics: the best-supported use
Antibiotics often upset the gut. The 2019 Cochrane review of 33 trials in children (6,352 participants) found antibiotic-associated diarrhea in 8% of those given probiotics versus 19% of controls, with moderate-certainty evidence. Doses of 5 billion colony-forming units (CFU) a day or more worked better than lower doses, and none of the 24 trials reporting on safety found serious side effects attributable to probiotics Guo 2019. NCCIH notes that a 2016 review did not show a benefit for this use in older people NCCIH.
C. difficile is a bacterium that can cause severe diarrhea after antibiotics. A 2017 Cochrane review of 31 trials (8,672 patients) found it in 1.5% of people on probiotics versus 4.0% of controls. The benefit appeared in trials where the baseline risk was above 5%, typically hospital patients, and not where risk was lowGoldenberg 2017. The AGA guideline suggests specific probiotics in this setting, while noting that people at low risk, or who place a high value on cost or on possible harms (especially if severely ill), could reasonably choose none Su 2020. If you are prescribed antibiotics, ask your prescriber or pharmacist whether a probiotic makes sense for you and how to time it.
Most other uses: unproven
The 2020 AGA guideline recommends probiotics only in the context of a clinical trial for people with C. difficile infection, Crohn's disease, ulcerative colitis and IBS, and suggests against them for children with acute infectious gastroenteritis Su 2020. That fits the Cochrane review of 82 studies of acute infectious diarrhea: it found probiotics probably make little or no difference to diarrhea lasting 48 hours or more Collinson 2020.
For colds and other upper respiratory infections, a 2022 Cochrane review of 23 trials found probiotics may reduce the number of people who get at least one infection and may shorten episodes by about a day, but most of the evidence was low certainty Zhao 2022. The close link between the immune system and gut microbes explains the interest; the trials so far are suggestive, not settled.
Many people take probiotics to "improve" their gut microbiome. In healthy adults, a systematic review of seven trials found no change in microbiota diversity, richness or evenness compared with placeboKristensen 2016. The gut microbiome page covers what diet studies show.
If you decide to buy one, choose by the strain and dose that were tested for your purpose, not by the total CFU count on the label. iHerb lists probiotic supplements; compare the strain names (for example, L. rhamnosus GG or S. boulardii) against the trials or your clinician's advice.
Who should not take them without medical advice
Safety
The risk of harmful effects from probiotics is greater in people with severe illnesses or weakened immune systems NCCIH. Severe and fatal infections have been reported in premature infants given probiotics. In 2023 FDA warned that preterm infants given probiotic products are at risk of invasive, potentially fatal infection from the organisms they contain, noted one infant death that year, and stated that it has not approved any probiotic as a drug or biologic for infants of any age NCCIH; FDA 2023.
The AGA guideline, published before that warning, suggested certain probiotic combinations for preterm, low-birth-weight infants in hospital to lower the risk of necrotizing enterocolitis Su 2020. Any decision about probiotics for a premature baby belongs with the neonatal care team.
Before you try it: safety and interactions
Who should avoid it or ask first
- You have a weakened immune system, a central venous catheter, or a serious illness: ask your care team first.
- The person is a premature infant: FDA has warned of invasive, potentially fatal infections; only the neonatal team should decide.
- You are relying on probiotics in place of medical care for persistent diarrhea, blood in the stool, or IBD symptoms.
Possible side effects
- Gas, bloating, nausea, rash and constipation were the common side effects in the children's antibiotic trials, at low rates similar to controls.
- Rare serious infections from the probiotic organism itself, mostly in very ill or immunocompromised people and premature infants.
Pregnancy and breastfeeding
Probiotic foods such as yogurt are ordinary parts of a pregnancy diet. Supplements have not been well studied for safety in pregnancy and breastfeeding, so check with your midwife or doctor before taking them. NCCIH; FDA 2023; Guo 2019
Medicine interactions
Check another food or medicine in the interactions list.
Common questions
Should I take a probiotic with antibiotics?
It is the best-supported use. A Cochrane review of 33 trials in children found antibiotic-associated diarrhea in 8% of those given probiotics versus 19% of controls, and another found fewer C. difficile infections in higher-risk patients. Ask your prescriber or pharmacist which strain and timing suit you.
Do probiotics change your gut microbiome?
In healthy adults, not measurably in most trials. A systematic review of seven placebo-controlled trials found no change in gut microbiota diversity, richness or evenness with probiotic supplements; only one trial found a shift in overall community structure.
Who should not take probiotics?
People who are seriously ill or immunocompromised should ask their care team first, because NCCIH says the risk of harm is greater for them. FDA has warned that premature infants given probiotic products are at risk of invasive, potentially fatal infections.
Do probiotics help IBS?
Possibly a little, but it is unproven. NCCIH says they may help overall symptoms and pain without definite conclusions on which strains work, and the American Gastroenterological Association recommends them for IBS only within clinical trials.
Sources
Primary research and government sources, each checked on the date this page was reviewed.
- CochraneGuo Q, et al. Probiotics for the prevention of pediatric antibiotic-associated diarrhea. Cochrane Database Syst Rev. 2019. PMID 31039287.
- CochraneGoldenberg JZ, et al. Probiotics for the prevention of Clostridium difficile-associated diarrhea in adults and children. Cochrane Database Syst Rev. 2017. PMID 29257353.
- CochraneCollinson S, et al. Probiotics for treating acute infectious diarrhoea. Cochrane Database Syst Rev. 2020. PMID 33295643.
- CochraneZhao Y, Dong BR, Hao Q. Probiotics for preventing acute upper respiratory tract infections. Cochrane Database Syst Rev. 2022. PMID 36001877.
- GuidelineSu GL, et al. AGA Clinical Practice Guidelines on the Role of Probiotics in the Management of Gastrointestinal Disorders. Gastroenterology. 2020. PMID 32531291.
- PubMedKristensen NB, et al. Alterations in fecal microbiota composition by probiotic supplementation in healthy adults: a systematic review of randomized controlled trials. Genome Med. 2016. PMID 27159972.
- NCCIHNational Center for Complementary and Integrative Health. Probiotics: Usefulness and Safety.
- FDAU.S. Food and Drug Administration. FDA Raises Concerns About Probiotic Products Sold for Use in Hospitalized Preterm Infants. 2023.
Keep reading
- GoalFood and digestive comfort: bloating, gas and sensitive gutsFor a sensitive gut, enteric-coated peppermint oil and a short, dietitian-guided low FODMAP trial have the strongest evidence. Most bloating comes from what and how fast we eat.
- GoalFood and the gut microbiome: fiber, fermented foods and probioticsMicrobiome science is young. A varied, fiber-rich diet is sensible on many grounds, one small trial found fermented foods raised microbe diversity, and probiotic evidence is strain- and condition-specific.
- RemedyYogurt and kefirCultured milks with the clearest evidence of any fermented food: their live bacteria help digest lactose. Other claims rest on probiotic supplement trials or observational data.
- RemedyFermented foodsSauerkraut, kimchi, miso, kefir and kombucha. One well-run trial suggests eating more of them changes the gut microbiome; claims beyond that are mostly untested in people.
- ComparisonKefir vs yogurtTwo fermented milks with different microbes: yogurt from two defined bacteria, kefir from grains holding bacteria and yeasts. For lactose, both work about equally in the one trial that compared them. For most other claims, the evidence is thin for both.