Lactobacillus acidophilus and Related Species: What Is Known

What is known about Lactobacillus acidophilus and related species: why species-level claims fall short, and what trials found for named strains and mixtures that include it.

Content last updated October 22, 2026. This page has not been medically reviewed.

Water-soluble vitaminLactobacillus acidophilus

What is Lactobacillus acidophilus and the acidophilus group good for?

What the body uses it for, and how strong the evidence is. A normal job in the body is not proof that extra supplements add benefit; each card says which.

Normal member of the gut and body microbiota

Not enough evidence

L. acidophilus is a species of lactic acid bacteria found in the human gut, mouth and vagina and in fermented foods.

Supplements: Not a nutrient; being present naturally does not show that a supplement helps.

Diarrhoea linked to C. difficile in people taking antibiotics

Clinically supported

One mixture of L. acidophilus CL1285 and L. casei LBC80R lowered C. difficile diarrhoea versus placebo in trials (low certainty).

Supplements: Evidence is for a named mixture only; AGA rated certainty low.

Antibiotic-associated diarrhoea in adults

Preliminary or mixed

A mixture of L. acidophilus CL1285, L. casei LBC80R and L. rhamnosus CLR2 showed efficacy in a strain-level review, while other Lactobacillus strains did not.

Supplements: Applies to the named mixture only.

Irritable bowel syndrome symptoms

Preliminary or mixed

A 2-strain mixture of L. acidophilus SDC 2012 and SDC 2013 improved pain in a single trial; AGA rated overall IBS certainty low.

Supplements: Low or very low certainty in each trial.

Pouchitis after colon surgery (8-strain mixture)

Not enough evidence

An 8-strain mixture that includes L. acidophilus is suggested by AGA over no probiotic (very low certainty).

Supplements: Very low certainty.

Immune boost and general gut health claims

Not enough evidence

Common marketing claims; sources we read do not show proven benefit for healthy people.

Supplements: No verified benefit in people with adequate health.

Connected topics

Open a group to see how each topic connects and how strong the evidence is.

Health goals (2)

Digestive SupportPreliminary or mixed
Specific acidophilus products have been tested for diarrhoea and IBS with mixed, low-certainty results. A result for one strain cannot be carried to another.
Gut HealthPreliminary or mixed
Probiotic effects are strain-specific, and this is a species name, not a strain. A few named acidophilus strains or mixtures have trial support for specific gut conditions; the species on its own has little evidence.

Body systems (2)

Digestive SystemPreliminary or mixed
Acidophilus is a normal gut and body resident; trials of specific products in diarrhoea and IBS give mixed, low-certainty results.
Gut HealthPreliminary or mixed
Named acidophilus strains have been tested for diarrhoea, C. difficile and IBS with low-certainty results; the species alone has little evidence.

Body parts (2)

GutPreliminary or mixed
Lactobacilli live in the gut; supplement trials focus on diarrhoea and IBS, with results that depend on the exact strain.
Large IntestinePreliminary or mixed
The conditions studied (C. difficile diarrhoea, antibiotic-associated diarrhoea) mainly affect the large intestine; benefit applies only to the specific tested mixture.

Functional actions (1)

Digestive SupportPreliminary or mixed
Used for diarrhoea and IBS in specific products; AGA rated the overall certainty low.

Root causes (2)

Digestive DysfunctionPreliminary or mixed
Tested in IBS and diarrhoea with mixed, low-certainty evidence that depends on the exact strain or mixture.
Medication Side EffectsPreliminary or mixed
One specific mixture (L. acidophilus CL1285 plus L. casei LBC80R) lowered C. difficile diarrhoea in people taking antibiotics (low certainty). It does not apply to other acidophilus products.

Conditions & symptoms (3)

Antibiotic-Associated DiarrheaPreliminary or mixed
A named three-strain mixture containing L. acidophilus CL1285 showed efficacy in adults while other Lactobacillus strains did not; NCCIH calls the overall benefit tentative.
Clostridium Difficile DiarrheaClinically supported
One mixture (L. acidophilus CL1285 with L. casei LBC80R) lowered C. difficile diarrhoea in people on antibiotics in trials, low certainty. Not shown for other acidophilus products.
Irritable Bowel SyndromePreliminary or mixed
A 2-strain mixture of L. acidophilus SDC 2012 and SDC 2013 improved pain in one trial; AGA rated overall certainty low and NCCIH says definite conclusions are not possible.

Documented risks and interactions (2)

Risk of infection in severely ill or immunocompromised people. Lactobacillus bloodstream infection is rare but carries higher death risk; risk factors include severe illness, immune suppression, intensive care and central lines.
Product quality and labelling. Some products contain microorganisms not named on the label, and shop products can differ from those tested in trials.

Explore all 12 gut supplements

Quick answer

"Acidophilus" is one of the best-known probiotic names, but the evidence is thin for the species on its own. Most useful trial results belong to named strains or fixed mixtures that happen to contain L. acidophilus, so they cannot be credited to the species. [1] We searched PubMed for placebo-controlled trials and meta-analyses of single L. acidophilus strains; apart from the trials below, Proper evidence not found.

What the name covers

L. acidophilus is a species in the emended genus Lactobacillus, which after the 2020 reclassification holds host-adapted species such as L. delbrueckii, L. crispatus and L. johnsonii. [2] A label that reads "acidophilus" names a species, not a strain. The strain code (for example CL1285 or NCFM) is what links a product to a study. NCCIH (US) warns that a benefit seen with one Lactobacillus does not mean another would do the same. [3] Probiotic yogurt and supplement are not interchangeable either: the NHS says there is likely a huge difference between products that show promise in trials and the yogurts and supplements sold in shops. [4] For foods see yogurt.

Evidence labels: promising but limited, mixed, insufficient evidence, no good evidence of benefit. "CoE" is certainty of evidence. Amounts are study amounts, not advice.

What research and official bodies found

Question	What the source found	Label
Children's acute diarrhea, L. acidophilus alone	Seven trials; four used heat-killed preparations that do not meet the strict definition of a probiotic. Diarrhea was about 7.8 hours shorter, but the range included no difference (very low CoE). [5] ESPGHAN gave a weak recommendation (very low quality) for heat-inactivated L. acidophilus LB, noting it does not fit the definition of a probiotic. [6]	Insufficient evidence
Diarrhea from any cause, L. acidophilus plus L. bulgaricus (helveticus)	A 2022 meta-analysis of four trials found diarrhea only 3.5% less common than with placebo, which the authors called of little or no clinical importance. [7]	No good evidence of benefit
Preventing C. difficile diarrhea in people on antibiotics, L. acidophilus CL1285 plus L. casei LBC80R	Risk ratio 0.22 versus placebo (low CoE). [5] The AGA guideline suggests this pair, or certain 3- and 4-strain mixtures, as options (conditional recommendation, low quality). [8]	Promising but limited
Preventing antibiotic-associated diarrhea in adults	The mixture of L. acidophilus CL1285, L. casei LBC80R and L. rhamnosus CLR2 showed efficacy, while other Lactobacillus strains did not. [1]	Promising but limited
IBS	A 2-strain mixture of L. acidophilus SDC 2012 and SDC 2013 improved pain in a single trial; one 6-strain mixture was worse than placebo for global symptoms. The AGA graded overall certainty as low. [5]	Insufficient evidence
Infant colic, L. acidophilus NCFM drops	In a 2026 trial of 60 infants the main outcome (responders at day 28) did not differ from placebo. [9]	No good evidence of benefit
Pouchitis (after colon surgery), 8-strain mixture that includes L. acidophilus	The AGA suggests it over no probiotic (conditional recommendation, very low quality). [8]	Insufficient evidence

The AGA guideline recommends probiotics for IBS, Crohn's disease and ulcerative colitis only in the context of a clinical trial, and suggests against them for children's gastroenteritis in North America. [8] None of these results can be carried to a different acidophilus strain or to a mixture with other ingredients.

Frequently asked questions

Is acidophilus a good probiotic?

It depends on the strain and the purpose. For L. acidophilus alone in children's diarrhea the evidence was very uncertain. [5]

What is the difference between acidophilus and Lactobacillus?

Acidophilus is one species inside the genus Lactobacillus. [2]

Does acidophilus help after antibiotics?

One specific mixture containing it (CL1285 with LBC80R) lowered C. difficile diarrhea in trials, with low certainty. [5] That does not apply to other acidophilus products.

Does acidophilus in yogurt count?

The sources we read do not compare yogurt and supplement strains; the NHS says yogurts and supplements sold in shops may differ greatly from products tested in trials. [4]

Should babies take acidophilus for colic?

A 2026 trial of one strain (NCFM) did not meet its main goal. [9] Talk to your baby's clinician first.

More details: evidence, limits and cautions

The details behind this page: cautions, limits of the evidence and where sources disagree. Open any note to read it.

Safety and who should ask first

The NHS says most people with a healthy immune system should not get unpleasant side effects, and advises talking to a doctor first if you have a health condition or weakened immune system. [4] NCCIH says harm is more likely in severe illness and some products have contained microorganisms not named on the label. [3] Lactobacillus bloodstream infection is infrequent but has a higher death rate, with severe illness, suppressed immunity, intensive care and central lines as risk factors. [10] Medicines, pregnancy, kidney or liver disease and surgery were not described for L. acidophilus in the sources we read (Proper evidence not found), so ask a clinician or pharmacist; see how medicine interactions work.

Severe or bloody diarrhea, fever, dehydration or illness in a baby needs medical care first, not a probiotic. [11] Related: Lactobacillus and Bifidobacterium overview and strain specificity.

References

McFarland LV, Evans CT, Goldstein EJC. Strain-Specificity and Disease-Specificity of Probiotic Efficacy: A Systematic Review and Meta-Analysis. Front Med 2018. PMID 29868585. Read 2026-10-22.
Zheng J et al. 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. PMID 32293557. Read 2026-10-22.
NCCIH (US National Center for Complementary and Integrative Health). Probiotics: Usefulness and Safety. Read 2026-10-22.
NHS (UK). Probiotics. Page last reviewed 24 November 2022. Read 2026-10-22.
Preidis GA et al. AGA Technical Review on the Role of Probiotics in the Management of Gastrointestinal Disorders. Gastroenterology 2020 (full text read via PMC8018518). PMID 32531292. Read 2026-10-22.
Szajewska H et al. J Pediatr Gastroenterol Nutr 2014. Use of probiotics for management of acute gastroenteritis: a position paper by the ESPGHAN Working Group for Probiotics and Prebiotics. PMID 24614141. Read 2026-10-22.
Carona A et al. Front Gastroenterol 2022. A systematic review and meta-analysis of Lactobacillus acidophilus and Lactobacillus bulgaricus for the treatment of diarrhea. PMID 41822092. Read 2026-10-22.
Su GL et al. AGA Clinical Practice Guidelines on the Role of Probiotics in the Management of Gastrointestinal Disorders. Gastroenterology 2020 (guideline text read from a hosted copy of the published PDF). PMID 32531291. Read 2026-10-23.
Vaz SR et al. BMC Pediatr 2026. Lactobacillus acidophilus for infant colic and microbiota modulation: a randomized clinical trial. PMID 41998618. Read 2026-10-22.
Kullar R et al. Microorganisms 2023. Lactobacillus Bacteremia and Probiotics: A Review. PMID 37110319. Read 2026-10-22.
NHS (UK). Diarrhoea and vomiting. Read 2026-10-22.

Education, not medical advice. This page is for general information. It does not diagnose or treat any condition and is not a substitute for care from a qualified health professional. Natural does not automatically mean safe. Ask a clinician or pharmacist before changing your care, especially if you take medication, are pregnant or breastfeeding, or have a health condition.