Probiotics

Does the probiotic strain matter, and how do you choose one?

Updated 4 Nov 2026

Short answer

Yes. A 2018 review of 228 trials found that the effect of a probiotic depends on the exact strain and on the health problem. A result for one product does not necessarily carry over to another.[1] Expert groups name strains for this reason, and they look for trials of that strain, at a known dose, for the same problem.[2][3]

What a strain is

A full name has a genus, a species and a strain code. Lacticaseibacillus rhamnosus GG is one example.[2] Products can hold one strain or many, and many commercial products have never been tested in research studies.[2]

Evidence that the strain matters

The same family of microbes can give different results:

  • Diarrhea from antibiotics. In adults, a mix of Lactobacillus acidophilus CL1285, Lactobacillus casei LBC80R and Lactobacillus rhamnosus CLR2 prevented it, and so did L. casei DN114001 and Lactobacillus reuteri 55730. Other Lactobacillus strains did not.[1]
  • Different problems. L. rhamnosus GG and Saccharomyces boulardii CNCM I-745 worked for some health problems, but not for others.[1]
  • Eczema in children. In one review, L. rhamnosus and Lactobacillus paracasei lowered the risk, while L. reuteri and L. acidophilus did not.[2]
  • Constipation. Stool frequency rose with Bifidobacterium lactis, but not with L. casei Shirota.[4]
  • Premature babies. Only multi-strain products lowered deaths in a comparison of 106 trials.[5]
  • Cholesterol. L. acidophilus and Lactobacillus plantarum lowered total and LDL cholesterol in a review of 30 trials, while Lactobacillus helveticus and Enterococcus faecium did not.[2]

Why reviews can mislead

Many reviews pool different probiotics into one result. The authors of the 2018 review warn that this can lead to misleading conclusions.[1] The results of a pooled review do not show that any one product works.[2]

What expert groups do

  • A European pediatric society makes a recommendation only when at least 2 randomized trials tested a similar, well-defined strain. It says that use of probiotics with no documented benefit should be discouraged.[3]
  • The World Gastroenterology Organisation advises only strains, doses and durations that helped in human studies.[2]
  • Some organizations have reviewed the evidence and name the product, dose and form for specific conditions.[2]

What labels show

  • Live count. Probiotics are counted in colony-forming units (CFU). A CFU count at the end of shelf life is more useful than one at manufacture, because microbes can die during storage.[2]
  • CFU for each strain. An international scientific association advises makers to list the total CFU, ideally for each strain, up to the use-by date.[2]
  • Storage. Some products need a refrigerator, and others can stay at room temperature.[2]
  • Contents. Some products contained microbes that were not on the label, and these can pose serious risks.[6]
  • New names. In 2020, Lactobacillus was split into 25 genera, including Lacticaseibacillus, Lactiplantibacillus and Limosilactobacillus. A strain may appear under a different genus name than in older studies.[7]

Sources (7)

  1. Strain-Specificity and Disease-Specificity of Probiotic Efficacy: A Systematic Review and Meta-Analysis. McFarland LV, Evans CT, Goldstein EJC Front Med (Lausanne), 2018. PMID 29868585
  2. Probiotics: Fact Sheet for Health Professionals. NIH Office of Dietary Supplements, 2025. ods.od.nih.gov
  3. Probiotics for the Management of Pediatric Gastrointestinal Disorders: Position Paper of the ESPGHAN Special Interest Group on Gut Microbiota and Modifications. Szajewska H, Berni Canani R, Domellöf M, Guarino A, Hojsak I, Indrio F, et al. J Pediatr Gastroenterol Nutr, 2023. PMID 36219218
  4. Probiotics and synbiotics in chronic constipation in adults: A systematic review and meta-analysis of randomized controlled trials. van der Schoot A, Helander C, Whelan K, Dimidi E Clin Nutr, 2022. PMID 36372047
  5. Probiotics, Prebiotics, Lactoferrin, and Combination Products for Prevention of Mortality and Morbidity in Preterm Infants: A Systematic Review and Network Meta-Analysis. Wang Y, Florez ID, Morgan RL, Foroutan F, Chang Y, Crandon HN, et al. JAMA Pediatr, 2023. PMID 37782505
  6. Probiotics: Usefulness and Safety. NIH National Center for Complementary and Integrative Health, 2019. www.nccih.nih.gov
  7. A taxonomic note on the genus Lactobacillus: Description of 23 novel genera, emended description of the genus Lactobacillus Beijerinck 1901, and union of Lactobacillaceae and Leuconostocaceae. Zheng J, Wittouck S, Salvetti E, Franz CMAP, Harris HMB, Mattarelli P, et al. Int J Syst Evol Microbiol, 2020. PMID 32293557

More about probiotics

What are probiotics?Do probiotics change your gut bacteria?Is a higher CFU count better?Which foods contain probiotics?What are probiotics used for?Do probiotics prevent diarrhea from antibiotics and C. difficile?

For education; not medical advice. Talk to a doctor before you start, stop or change a supplement.