Lactobacillus casei

Lacticaseibacillus casei · Lactobacillus paracasei · Lacticaseibacillus paracasei

Snapshot

Indications	Contraindications
Antibiotic-associated diarrhea^{1, 2} Acute diarrhea in children³ Common infectious diseases^{4, 5} Stress-related sleep disturbance⁶ Constipation in Parkinson's disease⁷ Irritable bowel syndrome⁸ Metabolic syndrome risk factors^{9, 10}	Immune-compromised conditions¹¹ Milk protein allergy¹²

Lactobacillus casei, now classified as Lacticaseibacillus casei and closely related to Lactobacillus paracasei, is a lactic acid bacterium sold as a probiotic whose effects are strain-specific. It acts on the gut microbiota and mucosal immune response.³ Supplementation is used mainly to prevent antibiotic-associated diarrhea² and to ease acute diarrhea in children³. It is also used to reduce common infections, for constipation in Parkinson's disease, and, as part of a multi-strain combination, for irritable bowel syndrome (IBS) symptoms^4–8.

Results elsewhere are less favorable: a trial in stable cirrhosis found that L. casei Shirota did not change infection rates compared with placebo¹³. A 2025 observational comparison in people with prior colorectal adenoma resection found long-term consumers of a Shirota strain preparation carried more butyrate-producing gut bacteria, without a cancer outcome¹⁴. More than four thousand products list Lactobacillus casei, mostly as capsules or powders, while fermented milk drinks deliver the Shirota strain; see Form comparison.

Health Canada lists a contraindication in immune-compromised conditions¹¹, and a case report described bacteremia from a matching probiotic strain in an infant with impaired intestinal integrity¹⁵. Health Canada labels ask for a practitioner's advice before use with fever, vomiting, bloody diarrhoea, or severe abdominal pain¹¹.

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

In the full monograph

67 sources, 49 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