Lactobacillus acidophilus

L. acidophilus

Snapshot

Indications	Contraindications
Irritable bowel syndrome^1–3 Antibiotic-associated diarrhea⁴ H. pylori eradication adjunct⁵ Lactose intolerance symptoms⁶ C. difficile prevention^{7, 8} Atopic dermatitis⁹	Immune-compromised conditions¹⁰ Milk allergy¹¹

Lactobacillus acidophilus is a lactic acid-producing bacterium first isolated from the human gut, and it acts largely by competitive exclusion of pathogens at the intestinal lining¹².

Evidence is strain-specific and mixed. A blend with Bifidobacterium outperformed placebo in non-constipated irritable bowel syndrome, while a two-strain acidophilus mixture did not separate from placebo on abdominal pain. In vitro, a 2023 study of dissolving electrospun fibers carrying L. acidophilus inhibited Gardnerella, a bacterium linked to bacterial vaginosis; the work is preclinical¹³. Products are mainly capsules and tablets, with 5599 products listing the ingredient; see Form comparison.

The main caution is invasive infection: a case report describes L. acidophilus bacteremia in a patient with acquired immunodeficiency syndrome¹⁴, and Health Canada lists immune-compromised conditions as a contraindication¹⁰. Health Canada labels also ask for practitioner consultation before use with fever, vomiting, bloody diarrhoea, or severe abdominal pain¹⁰.

Last updated October 16, 2026. Read how we make monographs.

In the full monograph

59 sources, 47 studies

When to useThe situations practitioners use it for, each with the reason and the study behind it.
SafetyWho should avoid it, who needs extra care, and the side effects reported in studies.
InteractionsThe medicines and supplements it interacts with, the effect of each, and what labeling says to watch.
Protocol notesThe doses used in studies, how and when they were taken, and how the forms on the market compare.
How it worksWhat it is and how it works in the body, in plain terms.
Published studiesThe studies behind each use, popular claims checked against them, and trials still under way.
Word of mouthWhat patients and practitioners report online, kept separate from the clinical evidence.
Clinical perspectiveA closing read of where the evidence is solid, where it is thin, and what has not been studied.

Snapshot

In the full monograph

Sources