Lactobacillus casei
Useful mainly for adults taking antibiotics who want to lower the risk of antibiotic-associated diarrhea.
Quick decision guide
May help most
Adults taking antibiotics who want to lower the risk of antibiotic-associated diarrhea
Common dosing range
1–30 billion CFU/day (commonly 5–30 billion for single strains)
When to expect effects
Days; take across the antibiotic course
Watch out for
Small risk of bacteremia in severely immunocompromised people
What is it
Lactobacillus casei (recently reclassified as Lacticaseibacillus casei) is a probiotic bacterium widely used in fermented dairy products and probiotic supplements. It is closely related to L. paracasei and L. rhamnosus and is studied for digestive, immune, and metabolic health.
Is it worth it for you?
Use this as a quick fit check, not a diagnosis.
Worth considering if…
Probably skip if…
Evidence at a glance
| Goal | Effect | Best fit | Time |
|---|---|---|---|
antibiotic-associated diarrhea prevention Good Evidence | Meaningful reduction in risk | Adults and older adults taking antibiotics | Days (over the antibiotic course) |
common cold duration and severity Limited Evidence | Modest, inconsistent | Older adults or stressed populations using strain-specific products | Weeks of consistent use |
irritable bowel syndrome Limited Evidence | Modest, inconsistent | People with IBS willing to trial a strain for several weeks | Weeks |
constipation in older adults Limited Evidence | Modest | Older adults with constipation | Weeks |
antibiotic-associated diarrhea prevention
- Effect
- Meaningful reduction in risk
- Best fit
- Adults and older adults taking antibiotics
- Time
- Days (over the antibiotic course)
common cold duration and severity
- Effect
- Modest, inconsistent
- Best fit
- Older adults or stressed populations using strain-specific products
- Time
- Weeks of consistent use
irritable bowel syndrome
- Effect
- Modest, inconsistent
- Best fit
- People with IBS willing to trial a strain for several weeks
- Time
- Weeks
constipation in older adults
- Effect
- Modest
- Best fit
- Older adults with constipation
- Time
- Weeks
Evidence for 4 uses
AI-assisted evidence assessment — talk to your doctor before relying on any single supplement.
antibiotic-associated diarrhea prevention
Supplement benefitSpecific L. casei strains, particularly in multi-strain drinks studied in hospitalized older adults, reduce the incidence of antibiotic-associated and Clostridioides difficile diarrhea. Benefit is strain- and dose-dependent and is strongest when started early in the antibiotic course. Evidence is good though effect sizes vary across populations.
Bottom line: A reasonable, evidence-backed option to reduce antibiotic-associated diarrhea when started promptly.
common cold duration and severity
Supplement benefitStrain Shirota and DN-114001 have been studied for upper-respiratory and cold symptoms, with some trials in older adults reporting modestly shorter or milder infections. Results are inconsistent and strain-specific, so benefit cannot be assumed for all L. casei products.
Bottom line: Possible modest, strain-specific benefit for colds, but evidence is limited and mixed.
Evidence is mixed
Some strain-specific trials show fewer or milder respiratory infections while others find no effect, and results may not generalize across strains.
irritable bowel syndrome
Supplement benefitL. casei has been studied as part of probiotic approaches to irritable bowel syndrome, with some reports of improved symptoms via barrier and immune modulation. Evidence is limited and inconsistent, and effects are strain-specific, so a multi-week personal trial is reasonable but not assured.
Bottom line: May modestly help some IBS symptoms, but evidence is limited and strain-dependent.
Evidence is mixed
Probiotic IBS trials are heterogeneous in strain, dose, and outcome, producing inconsistent results.
constipation in older adults
Supplement benefitFermented L. casei products have been studied for bowel regularity in older adults, with some trials reporting improved stool frequency. The evidence base is small and strain-specific, so benefit is preliminary.
Bottom line: May modestly improve regularity in older adults, but evidence is preliminary.
How it works
How to take it
What to track
3 commercial forms
Compare the main delivery options and what they’re best suited for.
L. casei Shirota
Found in Yakult fermented milk drinks. Has the most extensive research on digestive and immune outcomes.
Strong gastric acid survival, well-studied
L. casei DN-114001 (also called L. paracasei Defensis)
Studied for cold prevention and gastrointestinal symptoms in older adults.
Used in fermented dairy products
L. casei LC-11
Common in multi-strain capsule probiotic products.
Standard supplement-grade strain
Safety
Know the common side effects, key cautions, and who should avoid it.
Common side effects
Serious risks
Rare bacteremia in severely immunocompromised individuals
Who should avoid it
- Severely immunocompromised or organ-transplant patients on immunosuppression
- People with central venous catheters or critical illness (without physician input)
- Those with severe milk allergy if product is dairy-based
Pregnancy & breastfeeding
Generally well tolerated in pregnancy and breastfeeding.
Interactions
Antibiotics can kill the organisms; separate doses by at least 2 hours
Increase the small risk of bacterial translocation
Food sources
| Food | Amount | %DV |
|---|---|---|
| Yakult and similar fermented milk drinks | Approximately 10 billion CFU per bottle | — |
| Some yogurts (with added L. casei culture) | Varies; check label | — |
| Aged cheeses (variable) | Variable presence; not standardized | — |
Yakult and similar fermented milk drinks
- Amount
- Approximately 10 billion CFU per bottle
- %DV
- —
Some yogurts (with added L. casei culture)
- Amount
- Varies; check label
- %DV
- —
Aged cheeses (variable)
- Amount
- Variable presence; not standardized
- %DV
- —
Choosing a product
What to look for on the label — and what to be skeptical of.
Look for…
Be skeptical of…
Frequently asked questions
What's the difference between L. casei, L. paracasei, and L. rhamnosus?⌄
They are closely related species (now grouped under Lacticaseibacillus). Genetic reclassification has shuffled some strains between these names. They have overlapping but distinct documented effects.
Is Yakult a good source of L. casei?⌄
Yes. Yakult contains L. casei Shirota, the most-studied strain, at approximately 10 billion CFU per bottle. It also contains added sugar, which is worth considering.
Can L. casei help with constipation?⌄
Trials in older adults suggest modest improvement in stool frequency. Effects are not as strong as targeted fiber interventions but may complement other approaches.
How long until I notice effects?⌄
For acute conditions like antibiotic-associated diarrhea, effects appear within days. For chronic concerns, several weeks of consistent use are typical.
Can children take L. casei?⌄
Yes, L. casei has been used in many studies in children and is generally well tolerated. Discuss with your pediatrician for specific applications.
References by claim
antibiotic-associated diarrhea prevention
common cold duration and severity
irritable bowel syndrome
Track Lactobacillus casei with Pilora
Set up dose reminders, check interactions, and join the community in the Pilora iPhone app.
Coming to App StoreDisclaimer: These statements have not been evaluated by the FDA. This page is educational, not a substitute for personalized medical advice. Evidence grades are AI-assisted assessments — talk to your doctor before starting any new supplement, especially if you’re pregnant, breastfeeding, on medications, or managing a chronic condition.