Strain-by-Condition Evidence Matrix
Updated June 2026 · Sources: ISAPP, Cochrane, ESPGHAN, NIH ODS · Synthesised from our strain deep-dives
Most advice stops at "take a probiotic for IBS" or "take one after antibiotics" without naming a strain. That is the single most common mistake in this category: the strain, not the species, determines whether an organism works for a given condition. This matrix does the opposite. Pick a condition and it returns the specific strains that have published, evidence-graded support for it, with the clinical doses used in trials.
Every cell mirrors an evidence-graded section on the linked strain page - nothing here is a new claim. We grade three ways: Strong (multiple RCTs, meta-analyses, or guideline endorsement), Emerging (some RCTs, not yet replicated at scale), and Limited (weak or conflicting data). A dash means that strain's page does not grade that condition. For how the tiers are assigned, see our evidence methodology.
Pick a condition:
| Condition | L. rhamnosus GG | S. boulardii | L. acidophilus | B. longum |
|---|---|---|---|---|
| Acute infectious diarrhoea | Strong | Strong | — | — |
| Antibiotic-associated diarrhoea | Strong | Strong | — | — |
| C. difficile infection prevention | — | Strong | — | — |
| Traveller's diarrhoea prevention | — | Strong | — | — |
| IBS (general symptoms) | Limited | Limited | Emerging | Emerging |
| Constipation | — | — | — | Emerging |
| Atopic eczema prevention | Emerging | — | — | — |
| Lactose digestion | — | — | Strong | — |
| Vaginal health (BV / yeast) | — | — | Emerging | — |
| Immune modulation | — | — | Emerging | — |
| Gut-brain axis / mood | — | — | — | Emerging |
| Stress-related GI complaints | — | — | — | Emerging |
| Typical clinical dose | 10 billion CFU/day | 250-500 mg twice daily (~5 billion cells/capsule) | 1-10 billion CFU/day | 1-10 billion CFU/day |
How to read this matrix
The four strains across the top are the ones with full evidence reviews on this site. They are not the only strains worth knowing: B. infantis 35624 and L. plantarum 299v have the strongest IBS-specific evidence, B. lactis BB-12 and L. reuteri DSM 17938 lead on constipation, and psyllium fibre is the evidence-based first-line for regularity. Those appear on the relevant IBS and constipation condition guides. The matrix shows where the four most-studied strains land, not the whole field.
A dash is information, not an omission. It means that strain has no graded section for that condition on this site - usually because the trial evidence is absent or too weak to grade, not because the strain was overlooked. Treating "no evidence" as different from "negative evidence" is the whole point of grading honestly.