/ Probiotics Match my situation
Move · Gut

The right microbe for the right job.

Probiotics help with a few specific problems, and only when the strain was tested for that problem. Here is where the evidence holds, how to read a label, and how to run a fair trial on yourself.

Match my situation Read a label Evidence Check first

Evidence-checked, no brands, and not medical advice. Your trial log stays on this device.

01 · What counts

A probiotic is one named microbe, tested for one job.

The agreed definition is live microbes that, taken in a large enough amount, give a health benefit.[1] All three parts matter. It has to be alive when you take it, there has to be enough of it, and the benefit has to be shown in people.

LacticaseibacillusGenus rhamnosusSpecies GGStrain

Genus

The family name. In 2020 the old Lactobacillus genus was split into 25, so L. rhamnosus and Lacticaseibacillus rhamnosus are the same microbe under an old and a new name.[2]

Species

Like a first name. Many strains share it, and some effects are common to the species, mostly general gut support.[1]

Strain

The ID that links a product to its trials. This one is GG, also filed as ATCC 53103. The strongest results on this page come from named strains.

Its four cousins

These words turn up on the same shelf. Only the first one promises live microbes with a proven effect.[3]

This page

Probiotic

Live microbes that, in a large enough amount, give a health benefit.

A capsule of one named strain

Fermented food

Food made by microbes growing in it. It may or may not still hold live ones.

Yoghurt, kefir, kimchi, sauerkraut

Prebiotic

Food your gut microbes use in a way that gives you a health benefit.

Inulin, galacto-oligosaccharides

Synbiotic

Live microbes plus food they use, together giving a benefit.

A probiotic with added inulin

Postbiotic

Dead microbes or their parts, prepared so that they give a benefit.

Heat-killed bacteria

In Australia, yoghurt must carry at least 1 million live cultures per gram, and its one approved live-culture claim is easier lactose digestion.[4] Live cultures alone don’t make a food a probiotic.

The four you’ll see on labels

Lactobacilli

Now 25 genera, from Lactobacillus to Limosilactobacillus
Named strains
L. rhamnosus GG; L. reuteri DSM 17938
Best evidence
Antibiotic diarrhoea in children at high doses, and colic in breastfed babies.[10][22]

Bifidobacteria

Named for their split, Y-shaped cells
Named strains
B. animalis subsp. lactis; B. longum subsp. infantis
Best evidence
B. lactis adds bowel movements in constipation. Mixes help very premature babies, in hospital only.[19][23]

S. boulardii

Saccharomyces boulardii, a yeast, so antibiotics don’t kill it
Best evidence
Antibiotic diarrhoea and C. difficile prevention.[8][10]
Watch
Not with antifungal medicines or a central line.[13][33]

S. thermophilus

Streptococcus thermophilus, grows in chains
Where you meet it
A yoghurt starter culture, and part of one named 4-strain mix.[8]
Best evidence
With L. bulgaricus, it helps people who struggle with lactose digest yoghurt.[4]
02 · Match your situation

Pick what’s going on. See if a probiotic fits.

Each answer comes from trials and guidelines for that exact situation, with the strains that were tested. Where a guideline says no, so do we.

03 · Read a label

Ignore the big number. Find the strain.

Tap the numbered parts of this example label. It is invented, and it shows the things that matter and the things that only look like they do.

Daily probiotic · 30 capsules
Each capsule contains
04 · The evidence

What the evidence supports.

Graded from moderate to not shown. Nothing here reaches solid, because trials mix strains, doses and people, and many are small.

Moderate
High doses prevent antibiotic diarrhoea in children.
33 trials, 6,352 children: diarrhoea fell from 19% to 8%. At 5 billion CFU a day or more, it fell from 23% to 8%.[10]
Moderate
Probiotics prevent antibiotic diarrhoea in adults.
42 trials, 11,305 adults: risk down by about a third, with no benefit where the risk was low. In 2,941 inpatients aged 65 and over, no difference.[5][6]
Moderate
Probiotics protect very premature babies.
60 trials, 11,156 infants: fewer deaths (moderate certainty) and less necrotising enterocolitis, a serious bowel disease (low certainty). No clear effect in the most premature. Hospital use only.[23]
Moderate
B. lactis helps constipation.
It adds bowel movements a week, without softening stools or easing pain and bloating.[19]
Limited
Probiotics halve C. difficile diarrhoea.
38 trials, 13,179 people on antibiotics: 3.2% to 1.6%, low certainty. Worth it only where the risk is moderate to high.[12]
Limited
One strain eases colic in breastfed babies.
L. reuteri DSM 17938, 4 trials, 345 infants: about 25 minutes less crying a day by day 21. Not enough data in formula-fed babies.[22]
Limited
Probiotics ease IBS.
The British guideline says they may help, with very low quality evidence. The American College of Gastroenterology suggests against them.[17][18]
Limited
Probiotics prevent colds.
24 trials, 6,950 people: fewer had a cold (low certainty), and fewer needed antibiotics (moderate). Many different strains.[26]
Limited
Probiotics lift mood.
34 trials: a small effect on depression that shrank after allowing for unpublished studies, and a very small one on anxiety.[27]
Not shown
Probiotics treat gastro in children.
Two trials in 943 and 886 children found no difference in how sick they got or how long diarrhoea lasted.[21]
Not shown
Probiotics restore your gut after antibiotics.
In 21 adults, an 11-strain probiotic delayed the gut’s return to normal for months. One small study of one product.[15]
Not shown
Probiotics help you lose weight.
15 trials, 957 people with overweight: 0.6 kg over 3 to 12 weeks.[28]
Not shown
Probiotics prevent eczema and allergy.
Australia’s allergy society doesn’t recommend them for this. Results conflict and the best strain and dose are unknown.[25]
Myth
An AUST L number means it works.
Listed medicines use ingredients pre-approved as low risk. The TGA doesn’t assess whether the product works before it goes on sale.[29]
Myth
More strains make a better probiotic.
Guidelines name exact strains and mixes because effects depend on the strain. A strain count on the front is not evidence.[8]
05 · Trial it fairly

Run a 12-week trial on yourself.

For IBS and constipation, the honest answer is to try one and see. A weekly score makes that test fair, so you keep what works and stop paying for what doesn’t.

  1. One product at a time

    Write down the full strain name. If it works, that’s the one to buy again.

  2. Score the week before

    Your week-0 score is the baseline everything else is compared with.

  3. Change nothing else

    Same dose, same diet. Two changes at once and you can’t tell which one worked.

  4. Stop at 12 weeks if it hasn’t helped

    The British IBS guideline says to try one for up to 12 weeks, then stop if you’re not better.[17]

Week 0 is the week before you start. Score each week: 0 means none, 10 means the worst it gets. Lower is better.

We call a score 30% or more below your baseline “clearly better”. That’s our rule of thumb, not a medical cut-off. Your log saves on this device only.

06 · Check first

Who should skip them, and when to wait.

Probiotics are safe for most healthy people. Gas and bloating are the usual side effects.[31] These are the exceptions.

Weak immune system

healthdirect advises against probiotics for people on chemotherapy or immune-suppressing drugs, transplant recipients, people with HIV, and people who have just had surgery.[31]

Central line or intensive care

In a review of 59 blood infections with this yeast, 55 patients had a central line, and some caught it from capsules opened nearby.[13] In one children’s ICU, the capsule strain of L. rhamnosus reached the blood of 6 of 522 patients.[14]

Severe pancreatitis

In a trial of 296 patients with predicted severe acute pancreatitis, 16% died on a probiotic mix against 6% on placebo, and 9 had bowel ischaemia against none.[32]

Premature babies

In 2023 a premature baby died of sepsis from the bacterium in a probiotic product. The US FDA has approved no probiotic as a drug for infants.[24] Only the neonatal team decides.

On antifungal medicine

S. boulardii is a yeast, and its product information says not to take it with antifungals.[33] A bacterial strain is the logical alternative. That’s our inference, so ask your pharmacist.

Timing with antibiotics

Start within 2 days of the first antibiotic dose: later starts showed no clear benefit against C. difficile.[7] Leave about 2 hours between the antibiotic and a bacterial probiotic. That’s practical advice, not tested.[9]

See a GP, whatever you’re taking

A probiotic doesn’t fix these. Get them checked.

  • Watery diarrhoea three or more times a day during or after antibiotics, especially with fever or tummy pain
  • A fever while taking a probiotic, if you have a central line or a weak immune system (urgent)
  • A child with gastro who is drowsy, has fewer wet nappies, or can’t keep fluids down
  • Blood in your poo, or black poo
  • A change in bowel habit that lasts, or weight loss you can’t explain

Three questions for your pharmacist

  1. Which strain is in it, by its full name?
  2. How many CFU a day, guaranteed to the expiry date?
  3. Was this strain tested for my problem?
Sources33
  1. Hill C, Guarner F, Reid G, et al. The International Scientific Association for Probiotics and Prebiotics consensus statement on the scope and appropriate use of the term probiotic. Nat Rev Gastroenterol Hepatol, 2014.
  2. Zheng J, Wittouck S, Salvetti E, et al. A taxonomic note on the genus Lactobacillus: description of 23 novel genera. Int J Syst Evol Microbiol, 2020; and LPSN, Lacticaseibacillus rhamnosus.
  3. ISAPP consensus definitions: Gibson GR, et al. prebiotics, 2017; Swanson KS, et al. synbiotics, 2020; Marco ML, et al. fermented foods, 2021; Salminen S, et al. postbiotics, 2021. Nat Rev Gastroenterol Hepatol.
  4. Food Standards Code. Standard 2.5.3, Fermented milk products; and Schedule 4, Nutrition, health and related claims (live yoghurt cultures and lactose digestion).
  5. Goodman C, Keating G, Georgousopoulou E, Hespe C, Levett K. Probiotics for the prevention of antibiotic-associated diarrhoea: a systematic review and meta-analysis. BMJ Open, 2021.
  6. Allen SJ, Wareham K, Wang D, et al. Lactobacilli and bifidobacteria in the prevention of antibiotic-associated diarrhoea and Clostridium difficile diarrhoea in older inpatients (PLACIDE). Lancet, 2013.
  7. Shen NT, Maw A, Tmanova LL, et al. Timely use of probiotics in hospitalized adults prevents Clostridium difficile infection. Gastroenterology, 2017.
  8. Su GL, Ko CW, Bercik P, et al. AGA clinical practice guidelines on the role of probiotics in the management of gastrointestinal disorders. Gastroenterology, 2020.
  9. Williams NT. Probiotics. Am J Health Syst Pharm, 2010.
  10. 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.
  11. Szajewska H, Berni Canani R, Domellöf M, et al. Probiotics for the management of pediatric gastrointestinal disorders: position paper of the ESPGHAN Special Interest Group on Gut Microbiota and Modifications. J Pediatr Gastroenterol Nutr, 2023.
  12. 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.
  13. Muñoz P, Bouza E, Cuenca-Estrella M, et al. Saccharomyces cerevisiae fungemia: an emerging infectious disease. Clin Infect Dis, 2005; Rannikko J, et al. Fungemia and other fungal infections associated with use of Saccharomyces boulardii probiotic supplements. Emerg Infect Dis, 2021; and EMA CMDh, Saccharomyces boulardii: scientific conclusions, 2017.
  14. Yelin I, Flett KB, Merakou C, et al. Genomic and epidemiological evidence of bacterial transmission from probiotic capsule to blood in ICU patients. Nat Med, 2019.
  15. Suez J, Zmora N, Zilberman-Schapira G, et al. Post-antibiotic gut mucosal microbiome reconstitution is impaired by probiotics and improved by autologous FMT. Cell, 2018.
  16. Wastyk HC, Fragiadakis GK, Perelman D, et al. Gut-microbiota-targeted diets modulate human immune status. Cell, 2021.
  17. Vasant DH, Paine PA, Black CJ, et al. British Society of Gastroenterology guidelines on the management of irritable bowel syndrome. Gut, 2021.
  18. Lacy BE, Pimentel M, Brenner DM, et al. ACG clinical guideline: management of irritable bowel syndrome. Am J Gastroenterol, 2021.
  19. Dimidi E, van der Schoot A, Barrett K, et al. British Dietetic Association guidelines for the dietary management of chronic constipation in adults. J Hum Nutr Diet, 2025.
  20. Malfertheiner P, Megraud F, Rokkas T, et al. Management of Helicobacter pylori infection: the Maastricht VI/Florence consensus report. Gut, 2022.
  21. Schnadower D, Tarr PI, Casper TC, et al. Lactobacillus rhamnosus GG versus placebo for acute gastroenteritis in children; and Freedman SB, Williamson-Urquhart S, Farion KJ, et al. Multicenter trial of a combination probiotic for children with gastroenteritis. N Engl J Med, 2018.
  22. Sung V, D’Amico F, Cabana MD, et al. Lactobacillus reuteri to treat infant colic: a meta-analysis. Pediatrics, 2018.
  23. Sharif S, Meader N, Oddie SJ, Rojas-Reyes MX, McGuire W. Probiotics to prevent necrotising enterocolitis in very preterm or very low birth weight infants. Cochrane Database Syst Rev, 2023.
  24. US FDA. Warning regarding use of probiotics in preterm infants, 29 September 2023; and FDA raises concerns about probiotic products sold for use in hospitalized preterm infants, 26 October 2023.
  25. ASCIA. Allergy prevention FAQ, 2024; and Guidelines for infant feeding and allergy prevention, 2020.
  26. Zhao Y, Dong BR, Hao Q. Probiotics for preventing acute upper respiratory tract infections. Cochrane Database Syst Rev, 2022.
  27. Liu RT, Walsh RFL, Sheehan AE. Prebiotics and probiotics for depression and anxiety: a systematic review and meta-analysis of controlled clinical trials. Neurosci Biobehav Rev, 2019; and Asad A, Kirk M, Zhu S, Dong X, Gao M. Nutr Rev, 2025 (meta-analysis of 23 trials in clinically diagnosed patients).
  28. Borgeraas H, Johnson LK, Skattebu J, Hertel JK, Hjelmesæth J. Effects of probiotics on body weight, body mass index, fat mass and fat percentage in subjects with overweight or obesity. Obes Rev, 2018.
  29. TGA. How are vitamins regulated in Australia?; and Demonstrating the quality of listed probiotic medicines.
  30. Lewis ZT, Shani G, Masarweh CF, et al. Validating bifidobacterial species and subspecies identity in commercial probiotic products. Pediatr Res, 2016.
  31. healthdirect. Probiotics.
  32. Besselink MGH, van Santvoort HC, Buskens E, et al. Probiotic prophylaxis in predicted severe acute pancreatitis: a randomised, double-blind, placebo-controlled trial. Lancet, 2008.
  33. ANSM, base de données publique des médicaments. Ultra-Levure 200 mg, product information, section 4.5, 2024.
Start here

Match the strain to the job, or skip it.

Starting antibiotics is the clearest case for a probiotic. For everyday gut health, fibre and fermented food come first.

Match my situation Read a label Trial log Check first

Feed the microbes you already have with six gut smoothies