Evidence-based·Last reviewed May 30, 2026·How we grade evidence

Bacillus clausii

Probiotic

Useful mainly for people on antibiotics wanting to reduce diarrhea risk.

Quick decision guide

May help most

people on antibiotics wanting to reduce diarrhea risk

Common dosing range

2-4 billion CFU/day

When to expect effects

Days

Watch out for

avoid if severely immunosuppressed or critically ill

What is it

Bacillus clausii is a spore-forming probiotic bacterium used in supplements and pharmaceutical products to support gut health, particularly during and after antibiotic use.

Is it worth it for you?

Use this as a quick fit check, not a diagnosis.

Worth considering if…

You are taking a course of antibiotics
You want an acid- and heat-stable spore probiotic
You have had antibiotic-associated diarrhea before

Probably skip if…

You are severely immunosuppressed or critically ill
You have a central venous catheter
You develop fever or systemic symptoms on it

Evidence at a glance

acute infectious diarrhea

Limited Evidence
Effect
Small; uncertain
Best fit
People with acute diarrhea seeking an adjunct to rehydration
Time
Days

Evidence for 1 use

AI-assisted evidence assessment — talk to your doctor before relying on any single supplement.

acute infectious diarrhea

Disease adjunct
Limited Evidence

Some trials suggest B. clausii may modestly shorten acute infectious diarrhea, partly through antimicrobial peptide production and competition with pathogens. The evidence base is smaller and less consistent than for antibiotic-associated diarrhea.

Effect size
Small; uncertain
Time to effect
Days
Best fit
People with acute diarrhea seeking an adjunct to rehydration

Bottom line: May help shorten acute diarrhea, but evidence is preliminary.

SourceIaniro et al., 2018 — PMCSudha et al., 2019 — PubMed

How it works

Unlike many probiotics, B. clausii forms heat- and acid-stable spores, allowing it to survive stomach acid and reach the intestine intact. There it germinates, produces antimicrobial peptides, competes with pathogens for nutrients, and supports the intestinal mucosal barrier. Several strains are naturally resistant to common antibiotics, which has made the species useful as adjunct therapy during antibiotic courses to reduce diarrhea. In Europe and parts of Asia, B. clausii has been used pharmaceutically (Enterogermina) for decades.

How to take it

1. Typical dose
2-4 billion CFU/day
2. Timing
Any time of day; during and after an antibiotic course
3. With food
With or without food
4. How long to try
Through the antibiotic course and several days after

What to track

Stool frequency and consistency
Onset of any fever
Bloating or gas

2 commercial forms

Compare the main delivery options and what they’re best suited for.

B. clausii spores (single strain)

Standard probiotic and pharmaceutical form.

Spore form survives gastric acid intact.

Multi-strain spore probiotic

Used in broad-spectrum gut formulas.

Often combined with B. subtilis, B. coagulans.

Safety

Know the common side effects, key cautions, and who should avoid it.

Common side effects

Mild bloatingGas initially

Serious risks

  • Rare bacteremia in severely immunocompromised patients

Who should avoid it

  • Severely immunosuppressed
  • Critically ill
  • People with central venous catheters

Pregnancy & breastfeeding

Pregnancy data are limited but show no signal of harm at typical doses; consult a provider.

Interactions

AntibioticsMinor

Antibiotic-resistant strains are intended to be co-administered; non-resistant strains should be separated by 2-3 hours

Choosing a product

What to look for on the label — and what to be skeptical of.

Look for…

Named, characterized strain
Spore (heat-stable) form
Guaranteed CFU through shelf life

Be skeptical of…

Cures infections
Replaces rehydration therapy

Frequently asked questions

Why take it during antibiotics?⌄

Some B. clausii strains are antibiotic-resistant and can survive alongside the antibiotic to help maintain gut flora and reduce diarrhea.

Does it need refrigeration?⌄

No. Spores are shelf-stable at room temperature, which is an advantage over many probiotics.

References by claim

acute infectious diarrhea

Ianiro et al., 2018 — PMC (2018) link

Sudha et al., 2019 — PubMed (2019) link

Track Bacillus clausii with Pilora

Set up dose reminders, check interactions, and join the community in the Pilora iPhone app.

Coming to App Store
Evidence-based·Last reviewed May 30, 2026·Evidence current as of May 30, 2026·How we grade evidence

Disclaimer: 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.