Probiotic Strains: Evidence by Strain
Updated June 2026 · Sources: ISAPP, Cochrane, ESPGHAN, NIH ODS
The single most important fact in probiotics: the strain, not the species, determines what an organism does. Lactobacillus rhamnosus GG has excellent evidence for preventing antibiotic-associated diarrhoea in children; a different L. rhamnosus strain without a clinical designation may have no published evidence at all. When you read a label, look for the full strain code (for example "GG" or "ATCC 53103", "CNCM I-745", "DSM 17938") - a genus-and-species name alone tells you almost nothing about whether it works.
Each guide below grades the evidence for that strain by condition, using the same three-tier system applied across this site. For how we assign those tiers, see our evidence methodology page.
Strain Guides
Lactobacillus rhamnosus GG (LGG)
Strong EvidenceThe world's most-studied single strain (800+ clinical papers). Strongest evidence for paediatric acute diarrhoea and antibiotic-associated diarrhoea. Culturelle's flagship strain.
Saccharomyces boulardii CNCM I-745
Strong EvidenceThe only probiotic yeast - unaffected by antibiotics. Strongest evidence of any organism for antibiotic-associated diarrhoea, C. difficile prevention, and traveller's diarrhoea. Sold as Florastor.
Bifidobacterium longum
Emerging EvidenceStrains R0175 and NCC3001 studied for the gut-brain axis (anxiety/depression scores), IBS, and constipation. The leading 'psychobiotic' candidate, on emerging evidence.
Lactobacillus acidophilus
Emerging EvidenceThe classic yogurt-culture probiotic. Strains DDS-1 and NCFM studied for IBS and vaginal health. Widely sold but strain designation matters - much marketing omits it.