How we choose and how we are paid. Products are listed only when the certification we name can be checked in the certifier's own directory, or when they meet the nutrition criteria stated on this page. No company pays to appear here, and we earn nothing from these retailer links today. If that changes, every paid link will be labelled "(paid link)" next to it. We do not show prices because they change daily: check the retailer.
There is no single best probiotic. Buy the strain that was tested for your situation, such as Lacticaseibacillus rhamnosus GG or Saccharomyces boulardii CNCM I-745 for antibiotic courses, with a CFU count guaranteed to the end of shelf life. This guide follows the 2020 AGA guideline, the 2023 WGO guideline and Cochrane reviews from 2017 to 2020.
How we chose (criteria)
This page is a shopping aid, not a treatment plan. Our explainer on why the strain matters covers the science; here we turn it into a list of strain names you can type into a retailer search box. Every row had to pass four tests, checked on 18 October 2026.
- A named source. The strain or combination appears in the American Gastroenterological Association's 2020 guideline (AGA), in the World Gastroenterology Organisation's February 2023 global guideline (WGO), or in a Cochrane review.
- An honest grade. We state how strong the evidence is, and we say "not recommended" where a guideline says so. Where the AGA uses the word "suggest", that is its wording for a conditional recommendation, not a firm one.
- Search by strain first. The retailer links search for the strain name, not a brand, so you can compare every product that carries it.
- Brands only with proof on the brand's own page. A product is named only if its maker's official website shows the exact strain designation, and we link that page. We do not claim third-party certification for any of them: we could not match these exact products to a listing in NSF's dietary supplement directory when we checked, so look for a seal on the pack you buy.
No company has paid to appear here, and the order of rows follows the strength of evidence, not any brand.
Probiotics by use: the strains to search for
Read the "Evidence" column before the "Find it" column. Several rows end in "not recommended", and that is the most useful thing on the page: it can save you money.
| Use | Strain to look for | Evidence | What the guidelines say | Find it |
|---|---|---|---|---|
| Child on antibiotics, to prevent antibiotic diarrhoea | Lacticaseibacillus rhamnosus GG (LGG); Saccharomyces boulardii CNCM I-745 | Moderate (Cochrane 2019) | Overall protective effect; doses of 5 billion CFU a day or more did better; the authors want a large trial to confirm LGG and S. boulardii specifically | iHerb · Amazon |
| Adult on antibiotics, to prevent antibiotic diarrhoea | Saccharomyces boulardii CNCM I-745; LGG | Low to moderate | WGO reports a moderate effect in adults and older adults from meta-analyses; the size of benefit varies by strain | iHerb · Amazon |
| On antibiotics, to prevent C. difficile infection | S. boulardii; or L. acidophilus CL1285 with L. casei LBC80R; or the 3-strain mix of L. acidophilus, L. delbrueckii subsp. bulgaricus and B. bifidum; or the same 3 plus S. salivarius subsp. thermophilus | Moderate (Cochrane 2017); AGA conditional | AGA "suggests" these over no or other probiotics; the clearest benefit is where the baseline risk is high, such as a hospital stay | iHerb · Amazon |
| Irritable bowel syndrome | Bifidobacterium longum 35624; Lactiplantibacillus plantarum 299v (DSM 9843) | Very low to low | Not recommended by the AGA outside a clinical trial; WGO lists positive trials of specific strains; the British Society of Gastroenterology names no single strain | iHerb · Amazon |
| Stomach bug (acute infectious diarrhoea) | None | Moderate evidence of no effect | Not recommended: Cochrane 2020 found probiotics probably make little or no difference to diarrhoea lasting 48 hours or more; AGA advises against use in children | No product suggested |
| Crohn's disease or ulcerative colitis | None for routine use | Insufficient | Not recommended: AGA advises probiotics only within a clinical trial; WGO found no evidence of benefit in Crohn's | No product suggested |
| Pouchitis after bowel surgery | An 8-strain combination named by the AGA | AGA conditional; specialist use | AGA suggests it for adults and children; the choice belongs with your gastroenterology team | Ask your specialist |
| Digesting lactose | Yoghurt with live Streptococcus thermophilus and L. delbrueckii subsp. bulgaricus | Several controlled studies (WGO) | These two yoghurt cultures improve lactose digestion; this is a food choice, not a capsule | Amazon |
| No symptoms, "general gut health" | None | Very limited | No strain is recommended; fibre and fermented foods have a stronger case | No product suggested |
| Premature babies | Not a shop decision | Hospital use only | The FDA has warned of serious infections in preterm infants given probiotics | Neonatal team only |
Sources for the evidence column: Guo and colleagues, Cochrane 2019 on children's antibiotic diarrhoea (33 trials, 6,352 children); Goldenberg and colleagues, Cochrane 2017 on C. difficile; and Collinson and colleagues, Cochrane 2020 on acute infectious diarrhoea (82 trials). The WGO tables include only trials with a positive main result and did not grade risk of bias, so a strain appearing there is a lead to discuss, not proof that it works.
Probiotic after antibiotics: during, not only after
People often search for a probiotic "after antibiotics", but in the trials behind these reviews the probiotic was taken alongside the antibiotic course, not once it had finished. If you want to try one, buy it before you start, so the first dose is not delayed. S. boulardii is a yeast, so medicines that target bacteria do not target it. Ask your pharmacist how far apart to take the probiotic and your particular antibiotic, and whether either interacts with anything else you take.
Probiotic for IBS: a time-limited experiment
Because no IBS strain has strong backing, treat a purchase as a trial. Pick one product with one clearly named strain, keep the rest of your routine steady, note your symptoms for four weeks or more and stop if nothing changes. A dietitian-led low FODMAP diet has a firmer evidence base than any capsule, and our comparison of gut health supplements covers the alternatives.
Products whose own label names the strain
These four products are listed because each maker's website states the strain designation, not because they rank above other brands. We describe what the brand page shows, nothing more. Many shop-brand and pharmacy products carry the same strains; the strain searches in the table above will find them.
| Strain | Product | What the brand's page shows | Third-party listing | Find it |
|---|---|---|---|---|
| Lacticaseibacillus rhamnosus GG | Culturelle Digestive Daily Probiotic | Formulated with Lactobacillus rhamnosus GG | Not matched to this product | iHerb · Amazon |
| Saccharomyces boulardii CNCM I-745 | Florastor | Saccharomyces boulardii CNCM I-745 | Not matched | iHerb · Amazon |
| L. acidophilus CL1285, L. casei LBC80R, L. rhamnosus CLR2 | Bio-K+ | These 3 strains in most of its products | Not matched | Amazon |
| Bifidobacterium longum 35624 | Align | Bifidobacterium longum 35624 | Not matched to this product | iHerb · Amazon |
Two details matter. The AGA guideline names a two-strain combination, CL1285 with LBC80R, while the Bio-K+ site lists those two plus CLR2, so the match is close but not identical: check which formula a trial used before relying on it. And B. longum 35624 sits in the IBS row, where the AGA's advice is to use probiotics only within trials.
How to read strain, CFU and testing claims
The three numbers and names on a probiotic pack are where products differ most. Here is what each one should look like, and the warning signs.
The strain designation
A full name has three parts: genus, species and a strain code. The code is the part that links a capsule to a study. It may be a short name (GG, 299v, 35624) or a culture-collection deposit number such as ATCC 53103, DSM 17938 or CNCM I-745. WGO notes that strain designations and trade names are not controlled by the scientific community, and that manufacturers are expected to deposit their strains in a recognised collection, which is where those numbers come from.
Watch for:
- Labels that stop at the species, for example "Lactobacillus acidophilus" with no code.
- "Proprietary blends" that list ten species but no amounts for each.
- Old and new genus names for the same organism. Since 2020 many Lactobacillus species have new genus names, so L. rhamnosus GG and Lacticaseibacillus rhamnosus GG are the same strain.
CFU at the end of shelf life
Colony-forming units (CFU) estimate how many organisms are alive. Counts fall during storage, so a figure "at time of manufacture" can be far higher than what is left when you open the pack. Look for wording such as "guaranteed through expiry" or "at end of shelf life". A milligram weight alone tells you nothing about how many organisms survived.
More is not automatically better. WGO gives the example of B. longum 35624, which was effective for IBS symptoms at 100 million CFU a day, while other products need hundreds of billions. The right dose is the dose used in the trials for that strain. For children on antibiotics, the Cochrane review's higher-dose subgroup used 5 billion CFU a day or more.
Third-party testing
A seal from a body such as NSF or USP checks something narrower than most people assume. NSF's dietary supplement listing states that certified products have been tested to contain the identity and quantity of the ingredients declared on the label, without unacceptable levels of contaminants. That is valuable, but it says nothing about whether the strain helps your symptoms. Our guide to third-party tested supplements explains each seal, and the site's supplements section covers wider buying rules.
Fermented foods on the same trip
If you are buying yoghurt or kefir rather than capsules, the label rules are looser. US yoghurts may carry a "live and active cultures" statement, and many kefirs list their cultures by species, but few give strain codes or a count at the end of shelf life. Treat them as good everyday foods rather than as a dose of a tested strain, and choose plain versions so the sugar stays low. Chilled storage matters for these too.
How to check a probiotic label yourself
Use this checklist in the shop or on a retailer page. If a product fails the first two points, move on.
- Strain code present. Genus, species and strain designation for every organism.
- Strain matches your use. Find the strain in the table above, or ask your pharmacist or dietitian whether it has been tested for your problem.
- CFU per daily dose, at expiry. Not per bottle, and not only at manufacture.
- Dose close to the trials. If the studied dose was twice a day, a once-daily product is a different intervention.
- Storage. If the label says "refrigerate", buy it from a chilled shelf and keep it cold.
- A testing seal you can look up. Check the product in the certifier's own directory, not just the logo.
- No disease claims. In the US a supplement may describe effects on body structure or function but may not claim to treat a disease; a pack that promises a cure is a red flag.
- One change at a time. Start a probiotic in a week when nothing else in your diet changes, so you can judge it.
Do not start a probiotic without your medical team's agreement if you are immunocompromised, seriously ill, have a central venous catheter or are caring for a premature baby. The Cochrane review in children noted that serious adverse events have been reported outside trials in severely debilitated or immunocompromised children, including those with central lines.
Outside the US
The strain advice travels; the shelves and the labelling rules do not. Retailer stock differs by country, and the links on this page search US stores.
- United Kingdom. Probiotics are sold as food supplements, without pre-approval. The UK advertising regulator treats the word "probiotic" on a food as an implied health claim that needs authorisation, and none has been authorised (ASA advice on probiotic claims), so packs often say "live cultures" or "friendly bacteria" instead. The strain code is still the thing to look for.
- Canada. Probiotic capsules are natural health products. Look for the NPN (Natural Product Number) on the label and check it in Health Canada's Licensed Natural Health Products Database, which shows the licensed strains, amounts and wording.
- Australia. Probiotic capsules are regulated as complementary medicines, and most complementary medicines are listed on the Therapeutic Goods Administration's register with an AUST L number on the label (Cancer Council NSW). You can search that number in the TGA's ARTG.
When to see a dietitian
A probiotic is a reasonable experiment for a few specific situations, and a waste of money for many others. See a dietitian or doctor first if you have ongoing bloating, a change in bowel habit, or symptoms that wake you at night, because a capsule cannot tell IBS from coeliac disease, inflammatory bowel disease or a low-fibre diet. If you have Crohn's disease or colitis, keep probiotic decisions with your specialist team.
For most people, the cheaper first steps are food: more fibre, built up gradually, using the high-fibre foods list, plus some fermented foods with live cultures. Our guides to prebiotics and probiotics and improving gut health cover that ground, and the healthy eating check shows where your diet stands before an appointment.
Book a session with a dietitian
Frequently asked questions
What is the best probiotic to take?
There is no single best probiotic, only strains with evidence for particular uses. For a course of antibiotics, the strongest options are Saccharomyces boulardii CNCM I-745 and Lacticaseibacillus rhamnosus GG, plus the multi-strain combinations the AGA names for C. difficile. For IBS, evidence is weak and the AGA advises probiotics only in trials. Choose by strain code and dose, not by brand or CFU size.
Which probiotic is best for IBS?
No strain has strong evidence. The AGA recommends probiotics for IBS only in clinical trials, and the British Society of Gastroenterology names no specific strain. The WGO guideline lists positive trials for strains such as Bifidobacterium longum 35624 and Lactiplantibacillus plantarum 299v. If you try one, use a single named strain for four weeks or more and stop if nothing improves.
What probiotic should I take after antibiotics?
The trials started probiotics during the antibiotic course, not afterwards. Strains with the most support are Saccharomyces boulardii CNCM I-745 and L. rhamnosus GG. A 2019 Cochrane review in children found a moderate protective effect, stronger at 5 billion CFU a day or more. Ask your pharmacist about spacing doses, and get medical advice first if you are immunocompromised.
Do I need a probiotic with billions of CFU?
Not necessarily. The useful dose is the one tested for that strain. WGO notes that B. longum 35624 worked for IBS symptoms at 100 million CFU a day, while some other products are studied at hundreds of billions. What matters most is that the label guarantees the count at the end of shelf life, not just at manufacture.
Are probiotics recommended for a stomach bug?
Generally no. A 2020 Cochrane review of 82 trials found that probiotics probably make little or no difference to how many people have diarrhoea lasting 48 hours or longer, and the AGA advises against them for children with acute infectious gastroenteritis. Fluids matter more. Seek medical help for blood in stools, high fever, signs of dehydration or diarrhoea lasting more than a few days.
Does a third-party seal mean a probiotic works?
No. A seal from NSF or USP confirms that the product contains what the label declares, in the stated amounts, without unacceptable contaminants. It does not test whether the strain improves symptoms. Use the seal to judge quality and the strain evidence to judge usefulness, and look the product up in the certifier's own directory rather than trusting a logo.
Why are the strain names on my probiotic different from older articles?
In 2020 the Lactobacillus genus was split into many new genera, so the same organism can appear under two names. Lactobacillus rhamnosus GG is now Lacticaseibacillus rhamnosus GG, and Lactobacillus plantarum 299v is Lactiplantibacillus plantarum 299v. The strain code, such as GG or 299v, did not change, which is why it is the most reliable thing to search for.
