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Lactobacillus acidophilus
The most widely sold probiotic species — and one whose evidence sits at the STRAIN level, not the species level: NCFM, DDS-1, La-14 and La-5 are not interchangeable.
What the evidence says
L. acidophilus doesn't have enough studies with structured effect-size data yet to pool a verdict. Browse the studies below for individual findings.
Most evidence is from high-quality randomised trials published 1999–2026 with a typical study size of 2,981 participants.
Based on 10 studies · 4 RCTs · 3,311 total participants
Confidence
Moderate confidenceBy outcome
Several small human randomised trials of named strains report benefits: DDS-1 alone reduced abdominal pain in a 330-person IBS trial and eased lactose-intolerance symptoms in a crossover trial, and fermented milk carrying strain L1 lowered cholesterol by about 3%. FDA has closed multiple GRAS notices for named strains without objection. Against that: each use rests on a single trial, the largest relevant prevention trial (PLACIDE) found no benefit, and the FAO/WHO consultation records that no efficacy data had been generated for one of the species' most popular uses.
22 trials ongoing or recruiting · 178 completed on ClinicalTrials.gov
16 of the completed trials have posted results
Registered trials show research momentum for L. acidophilus, not proof of effect — a registration is a plan, and posted results are sponsor-reported, not peer-reviewed. They are never counted toward the evidence rating above.
Browse these trials on ClinicalTrials.govClinicalTrials.gov · as of Oct 2026
Under EU law (Reg. 1924/2006), EFSA reviews whether a specific health claim for L. acidophilus meets the evidence standard. These are independent regulatory decisions on claims — not studies, and never counted toward the evidence score above.
Not authorised by EFSA
“Lactobacillus LA-5 [In german : ] Begünstigt die Darmflora”
“Probiotic strain: Lactobacillus acidophilus LA-5 Improves the absorption of lactose”
“Lactobacillus acidophilus CNCM I-1722 '- probiotic -helps maintain a healthy gut flora”
“Probiotic strain: Lactobacillus acidophilus LA-5 Helps to improve natural bowel movements”
“Lactobacillus acidophilus Lafti L10 (CBS 116.411) '- probiotic -improves your feeling of (intestinal) comfort”
“Lactobacillus acidophilus LA- 5® Supports/promotes a healthy vaginal microflora Supports/promotes vaginal health”
“Probiotic strain: Lactobacillus acidophilus LA-5 Helps to restore the intestinal microbiota during and after antibiotic use”
“Lactobacillus acidophilus LA14 Helps to restore and maintain normal vaginal microflora; Helps during the treatment of urogenital disorders”
“Lactobacillus acidophilus THT 030102 * Helps to strengthen natural defences * Stimulates immune system * Strengthens resistance of organism”
“Lactobacillus acidophilus rhamnosus LR(3) Helps to restore and maintain normal vaginal microflora; Helps during the treatment of urogenital disorders”
“Not authorised” means the specific claim wording did not meet the EU’s evidence standard — often a matter of dossier or phrasing, not proof of no effect. EFSA judges marketing claims and is kept separate from our study-based evidence score.
Source: EU Register of nutrition and health claims (European Commission / EFSA) · register snapshot Feb 2013
Lactobacillus acidophilus (NCBI Taxonomy ID 1579) is a lactic acid bacterium and the species most commonly named on a probiotic label.
It kept the genus name Lactobacillus through the 2020 reclassification that split the genus into 23 new genera — the paper's title records an 'emended description of the genus Lactobacillus' rather than a new name for it (PMID 32293557).
It is not, however, the type species of that genus; that is L. delbrueckii (LPSN, lpsn.dsmz.de/genus/lactobacillus).
What matters most for a buyer is that the evidence is strain-specific: FDA has closed GRAS notices without objection for L. acidophilus DDS-1 at 10^9 to 10^11 CFU per serving in foods generally (GRN 871), for NCFM in non-exempt term infant and toddler formulas at 10^8 CFU/g (GRN 865) and in general food categories (GRN 357), for La-14 at 10^9 CFU per 250 g serving (GRN 502), and for KCTC 11906BP at up to 10^9 CFU per serving in liquid unflavoured milk (GRN 1083).
The FAO/WHO expert consultation defines a probiotic as 'live microorganisms which when administered in adequate amounts confer a health benefit on the host' (FAO Food and Nutrition Paper 85, 2006); the human trials for this species are individually small and mostly test one named strain, sometimes blended with a Bifidobacterium.
L. acidophilus LA 1 binds to cultured human intestinal cell lines and inhibits cell attachment and cell invasion by enterovirulent bacteria (PMID 8174985). This is in-vitro evidence for the competitive-exclusion idea, not a clinical outcome.
A randomised, double-blind, placebo-controlled crossover trial tested the DDS-1 strain for symptomatic relief in lactose intolerance (PMID 27207411).
The FAO/WHO expert consultation defines a probiotic as 'live microorganisms which when administered in adequate amounts confer a health benefit on the host' (FAO Food and Nutrition Paper 85, 2006). Viability at end of shelf life, not at manufacture, is what the definition turns on.
Discuss with a clinician first. The AHRQ evidence report found no statistically significant increase in adverse events in randomised trials (relative risk 1.00, 95% CI 0.93 to 1.07), but its case-study evidence points to compromised hosts as the group most likely to be harmed, and it concludes that the literature 'is not well equipped to answer questions on the safety of probiotic interventions with confidence' (PMID 23126627).
FDA closed a GRAS notice without objection for L. acidophilus NCFM in non-exempt term infant formula and toddler formulas at 10^8 CFU/g (GRAS Notice GRN 865). That is a regulatory no-objection for a specific strain in a specific product, not a paediatric efficacy finding, and it does not extend to other strains or to preterm infants.
No data. None of the sources consulted — the FAO/WHO probiotics report, the AHRQ safety evidence report, or the FDA GRAS notices — makes a statement about this species in pregnancy. Recorded as an absence, not as reassurance.
No data. As above: no source consulted addresses this species during breastfeeding.
PLACIDE enrolled 2,981 inpatients aged 65 and over and reported no benefit for preventing antibiotic-associated diarrhoea (PMID 23932219). It is the largest trial in this age group relevant to the species; its report describes the intervention as two lactobacilli and two bifidobacteria without naming them, so read it as evidence about probiotics in older inpatients rather than about this species specifically.
L. acidophilus has an evidence score of 5/10 — moderate evidence based on 10 indexed studies. The most widely sold probiotic species — and one whose evidence sits at the STRAIN level, not the species level: NCFM, DDS-1, La-14 and La-5 are not interchangeable. Representative study: PMID 23126627.
The commonly studied dose of L. acidophilus is 1-100 billion CFU (10^9 to 10^11) per serving — the range FDA reviewed without objection for L. acidophilus DDS-1 in foods generally (GRAS Notice GRN 871); La-14 was noticed at 1 billion CFU per 250 g serving (GRN 502) (the one cited trial that states a dose used 10 billion CFU a day). Individual needs vary — start at the lower end of the range and adjust based on how you respond.
Timing is flexible for L. acidophilus — consistent daily use matters more than the time of day. The GRAS notices cover this species as a food ingredient — in milk, formula, beverages and bars — so it has been assessed as something taken with food.
L. acidophilus is generally well-tolerated and considered safe for most healthy adults at recommended doses. Use caution if any of these apply to you: Severe immunocompromise, critical illness, or an indwelling central venous catheter — the AHRQ evidence report on probiotic safety describes case studies of fungaemia and some bacteraemia potentially associated with administered probiotic organisms, and states that participants with compromised health are most likely to experience adverse events (PMID 23126627).
Probiotics
Likely helpsLive microorganisms where strain selection determines outcome — Lactobacillus and Bifidobacterium strains best studied for gut, immune, and mood.
Saccharomyces Boulardii
Likely helpsAntibiotic-resistant probiotic yeast that supports digestive regularity and gut flora during travel and antibiotic use.
VSL#3 / Visbiome
Too few graded studiesAn 8-strain blend dosed in the hundreds of billions to trillions of CFU per day — roughly 45 to 7,000 times a typical 1-10 billion CFU consumer probiotic — with the largest effect size in the probiotic literature for one narrow use: maintaining remission in chronic pouchitis after ulcerative colitis surgery. It is null for IBS and Crohn's — and since 2016 the brand name no longer reliably identifies the formulation that was studied.
B. lactis (BB-12 / HN019)
Too few graded studiesThe most-replicated probiotic effect on gut transit — it measurably speeds things up and adds roughly one bowel movement a week in people who are already low. But it is not a constipation cure: the two largest, best-designed trials both missed their primary endpoints, and the honest effect is hours off transit time, not a fix.
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Reviewed by Dr. Baher Al Hakim · Last reviewed September 2026 · evidence from 10 studies · how we score · editorial policy
This information is for educational purposes only. It is not a substitute for professional medical advice. Always consult a qualified healthcare provider before starting, stopping, or changing any supplement or medication.