Probiotic strains compared: which strain for which condition

Updated 2026-05-13 · Reviewed by SupplementScore editors · No sponsorships · No affiliate links

The single most important fact about probiotics is also the most consistently ignored on labels and marketing copy: effects are strain-specific. Saying you took "a probiotic" is roughly as informative as saying you took "a drug." The species (Lactobacillus rhamnosus), the strain identifier (GG, or the alphanumeric code after the species name), the dose in CFU, and the duration are what actually predict whether a trial showed benefit. Generic "multi-strain blend" products with no strain identifiers are not necessarily harmful — but they're not what produced the trial evidence either.

TL;DR — which strain for which condition

The strain-specificity problem, plainly

Different strains of the same probiotic species can produce opposite effects on the same endpoint. Lactobacillus reuteri DSM 17938 reduces infant colic crying time in several RCTs; other strains of the same species do not. L. rhamnosus GG reduces antibiotic-associated diarrhea in pediatric and adult populations; other L. rhamnosus strains do not reproduce this consistently. The mechanism: strains differ in which surface proteins they express, which bacteriocins they produce, which host receptors they engage, and which immune signalling pathways they modulate. Calling them all "L. rhamnosus" is a taxonomic convenience, not a pharmacological identity.

The practical implication: a "L. rhamnosus 10 billion CFU" product without a strain identifier (the letter+number code after the species name) has not been validated for any specific indication. Labels that read "Lactobacillus rhamnosus GG", "Lactobacillus rhamnosus HN001", "Lactobacillus rhamnosus GR-1", etc. — those are different strains with different evidence portfolios. The international guideline bodies (WGO, AGA, ESPGHAN) are increasingly explicit: clinical recommendations are tied to specific strains and doses, not to "probiotics" as a category [1][2].

Lactobacillus rhamnosus GG (LGG)

LGG is the most-studied probiotic strain in the world — well over 250 published clinical trials. The largest evidence bases are for pediatric acute gastroenteritis (modest reduction in diarrhea duration; ESPGHAN recommends it as a conditional adjunct), antibiotic-associated diarrhea (positive in adults and children), and atopic dermatitis prevention when given perinatally to mothers and infants in atopy-risk families [3]. LGG is also one of the better-studied strains for community respiratory infection prevention in daycare children.

What LGG does not have strong evidence for, despite its popularity: IBS symptom improvement (mixed results), eczema treatment in already-affected children (Cochrane review found no benefit), and any of the mental-health endpoints sometimes pitched in "gut-brain axis" marketing. The default-multivitamin treatment of LGG as a generic gut supplement is not where the evidence sits.

Typical dose: 10 billion CFU/day. Available in dozens of branded products (Culturelle is the original consumer brand).

Saccharomyces boulardii CNCM I-745

S. boulardii is unusual: it's a yeast, not a bacterium, and as such it's resistant to antibiotics — which is what makes it useful during antibiotic therapy. The strain CNCM I-745 (sold as Florastor or Bioflor in many markets) has Cochrane-level evidence for antibiotic-associated diarrhea prevention in both adults and children, for acute infectious diarrhea, and for prevention of Clostridioides difficile recurrence in select adults [4]. It also has positive data for traveler's diarrhea prevention.

Two caveats. First, S. boulardii is not recommended in immunocompromised patients, patients with central venous catheters, or critically ill patients in intensive care, because case reports of S. boulardii fungemia exist when the yeast translocates across the gut barrier. The risk is small but real and the precaution is in major guidelines. Second, the antibiotic resistance that makes it useful during antibiotic therapy also means it does not meaningfully help repopulate a normal bacterial gut flora — for that, bacterial probiotics or fibre matter more.

Typical dose: 5–10 billion CFU/day (250–500 mg of the dried preparation), starting day 1 of antibiotics and continuing 7 days after the last dose.

Bifidobacterium infantis 35624 (Align)

B. infantis 35624 (now classified as Bifidobacterium longum subsp. longum 35624) is the strain in Align (the Procter & Gamble brand). It has the most consistently positive IBS trial portfolio of any single strain, with at least three large RCTs showing improvements in global IBS symptom scores, particularly in IBS-D and IBS-M subtypes. Mechanistic data suggest a modulation of cytokine signalling rather than colonisation; the strain typically does not persist in the gut after supplementation stops, which means continuous use is required for sustained benefit.

The trial-validated dose is 1 billion CFU/day for at least 4 weeks before assessing response. Buyers should know that effect sizes are modest (10–15 percentage points over placebo in global symptom relief) and that response is heterogeneous — some IBS patients have clinically meaningful benefit, many do not. The American College of Gastroenterology guidelines list probiotics conditionally for IBS without strong endorsement [5].

Lactobacillus helveticus R0052 + Bifidobacterium longum R0175 (Cerebiome / Probio'Stick)

This two-strain combination, often marketed as Cerebiome or Probio'Stick, has the largest single trial portfolio for psychobiotic endpoints (mood, perceived stress, anxiety symptoms). The original Diop 2008 RCT showed reductions in GI symptoms of stress; subsequent trials have shown modest reductions in self-reported anxiety symptoms and serum cortisol awakening response over 4–8 weeks of supplementation. The effect sizes are real but small, and the trial bar is "self-reported mood symptoms in non-clinical samples," not "treatment of major depressive disorder." Several trials have been industry-funded.

For someone exploring probiotics in the context of stress or low mood, this strain combination is the one with the most validated trial data. It is not a substitute for treatment of clinical depression or anxiety disorders, and it should not be presented as one [6].

Lactobacillus reuteri DSM 17938

L. reuteri DSM 17938 (sold as BioGaia drops, Gastrus, and in some children's formulations) is the standout strain for infant colic — reducing daily crying time in breastfed infants in multiple RCTs and a Cochrane review, with the largest signal in breastfed-only populations [7]. Other infant indications (regurgitation, functional constipation) have smaller but supportive data. For adults the strain has been studied for functional dyspepsia, oral health, and bone density, with smaller and less consistent signals.

This is one of the cleanest examples of strain-specificity: L. reuteri as a species has a long phylogenetic history, and most commercial L. reuteri strains are not DSM 17938. The colic trials do not generalise to "any L. reuteri product."

VSL#3 / Visbiome (8-strain combination)

VSL#3 (now sold as Visbiome in the US after a brand dispute; the same formulation in different jurisdictions) is an 8-strain combination of four Lactobacillus, three Bifidobacterium, and one Streptococcus thermophilus strain. The evidence base is concentrated in two indications: maintenance of remission in ulcerative colitis (multiple RCTs showing reduced relapse rates) and pouchitis prevention after ileal pouch–anal anastomosis (positive trials supporting use as adjunct). These are real clinical indications under physician supervision, not over-the-counter gut-health use [8].

Doses in these trials are high — 450 to 1800 billion CFU/day — which is one to two orders of magnitude above typical consumer probiotic dosing. The product is expensive at trial-validated doses, and use should be coordinated with a gastroenterologist.

Lactobacillus crispatus and other vaginal-health strains

L. crispatus is the dominant lactobacillus in the healthy human vagina, and intra-vaginal delivery of L. crispatus CTV-05 (Lactin-V) has positive RCT data for reducing bacterial vaginosis recurrence after standard antibiotic treatment. Oral combinations including L. rhamnosus GR-1 and L. reuteri RC-14 have separate evidence for vaginal microbiome restoration and reducing BV/yeast recurrence. The oral and intra-vaginal routes both have data; the strain identity matters more than the route.

For recurrent UTI, separate trials of oral L. rhamnosus GR-1 + L. reuteri RC-14 have shown modest reductions in recurrence rates in pre- and postmenopausal women. The evidence is real but less robust than for vaginal indications.

Multi-strain "broad-spectrum" probiotic blends

Most consumer probiotic shelves are filled with 10-strain, 25-strain, 50-strain blends marketed at high CFU counts. The evidence question for these is awkward: each individual blend is essentially its own intervention, and most have no published RCT data on the specific formulation. The exceptions (VSL#3/Visbiome, Probio'Stick, the multi-strain blends used in a few Cochrane-cited AAD trials) are well-characterised products with disclosed strains. The unlabelled "50 billion CFU multi-strain" products in the immune-health aisle are sold on category-level evidence that may not transfer to the specific blend in the bottle.

If you are buying a multi-strain product, it should: disclose each strain by alphanumeric code, list CFU counts per strain rather than per blend, and ideally cite the specific RCT in which that exact formulation was tested. The absence of these is a tell.

Head-to-head matrix by condition

Which strain should you pick — decision tree

Dose and the "CFU number" question

Higher CFU is not better in any monotonic way. The clinically effective dose differs by strain and indication: 1 billion CFU/day for B. infantis 35624 in IBS; 5–10 billion CFU/day for LGG in AAD; 1800 billion CFU/day for VSL#3 in UC maintenance. A 50-billion-CFU multi-strain product is not necessarily superior to a 1-billion-CFU single-strain product if the strain in the latter matches your indication and the strains in the former don't.

What does matter for any probiotic is the CFU count at expiry, not at manufacture. Many products lose viability during storage; better products disclose CFU at expiry or use stabilising delivery technologies (encapsulation, refrigeration-required formulations). The species and strain composition can drift in poorly QC'd products. Third-party testing (USP Verified, ConsumerLab) helps.

Evidence quality call-out

L. rhamnosus GG: Tier 2 (moderate-to-strong evidence). Largest trial portfolio of any single strain. Indication-dependent: strong for AAD and perinatal eczema prevention, weaker for IBS.

S. boulardii CNCM I-745: Tier 1 (strong evidence). Cochrane-supported for AAD; positive for acute and traveler's diarrhea. Contraindications matter.

B. infantis 35624: Tier 2 (moderate evidence). The most-replicated IBS strain. Effect sizes modest.

L. helveticus R0052 + B. longum R0175: Tier 3 (limited evidence). Modest psychobiotic signal; mostly industry-funded.

L. reuteri DSM 17938: Tier 2 (moderate evidence). Strongest for breastfed infant colic.

VSL#3 / Visbiome: Tier 2 (moderate evidence). Validated in UC maintenance and pouchitis at high doses under specialist care.

Generic multi-strain blends without disclosed strain codes: Tier 4 (insufficient evidence for the specific product).

Common misconceptions

"Probiotics restore your gut flora after antibiotics." The intuitive picture — that probiotic strains repopulate the gut and replace the bacteria killed by antibiotics — is mostly incorrect. Supplemented probiotic strains rarely colonise long-term; they transit and exert effects via immune signalling and short-chain fatty acid production during their passage. A 2018 trial actually suggested that probiotic supplementation can delay the return of native microbiome diversity after antibiotics in some adults, though the clinical significance of that finding is debated. The benefit of probiotics during antibiotic therapy is reducing diarrhea symptoms, not "restoring" anything.

"More strains is better." Number of strains per capsule is essentially a marketing variable, not an efficacy variable. Single-strain products (B. infantis 35624 in Align, S. boulardii CNCM I-745) have some of the strongest evidence portfolios. Adding ten more poorly-characterised strains to a bottle does not multiply the benefit.

"All Lactobacillus is the same." Already covered — strain identity is determinative. Even within the same species, different strains can have different effects and even different safety profiles.

"Probiotics are universally safe." For healthy adults and most children, the safety record is excellent at standard doses. The contraindications that matter: severe immunocompromise, central venous catheters in critically ill patients, premature neonates outside of specific protocols, and active bloodstream infection. Cases of probiotic-associated bacteremia and fungemia exist in these populations [9].

"Refrigerated probiotics are always better." Some strains require refrigeration to maintain viability; some are shelf-stable by design (lyophilised in specific encapsulations). Refrigeration vs shelf-stable is a product-specific question, not a quality marker on its own.

What we'd actually buy

For someone starting antibiotics: a Florastor-equivalent S. boulardii CNCM I-745, 250 mg twice daily, with the regimen extending 7 days past the last antibiotic dose. For IBS-D or IBS-M with no known structural pathology: an Align (B. infantis 35624) trial of 4–8 weeks at 1 billion CFU/day before deciding whether to continue. For a pregnant person in a high-atopy family with their obstetrician's approval: a Culturelle-equivalent LGG at 10 billion CFU/day perinatally. For a breastfed infant with colic and pediatrician approval: BioGaia drops (L. reuteri DSM 17938).

For someone with no specific complaint who wants to "support gut health": don't buy a probiotic first. Eat more fibre, eat fermented foods regularly, and reduce ultra-processed food. The dietary changes produce larger and more durable shifts in microbiome diversity than any probiotic supplement.

None of these recommendations are sponsored. Verified-tested brand options are listed on each strain's individual page (look for the "Verified brands" panel).