Quick answer
Antibiotics can disturb gut bacteria, sometimes causing diarrhoea. Health New Zealand names a probiotic as worth considering during a long or repeated antibiotic course. Systematic reviews of randomised trials support this, showing probiotics can meaningfully reduce antibiotic-associated diarrhoea risk — though not every strain or product carries the same evidence.
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Health New Zealand specifically names a probiotic as useful during a long or repeated course of antibiotics — this is a more targeted situation than "probiotics for general gut health."
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A large systematic review found probiotics taken alongside antibiotics reduced the risk of antibiotic-associated diarrhoea in adults, with a moderate overall quality of evidence.
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Not all probiotics are interchangeable: benefits for antibiotic-associated diarrhoea are strongest for specific, well-studied strains and adequate doses, not every product labelled "probiotic."
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Antibiotics can kill probiotic organisms too, so many pharmacists suggest spacing doses a few hours apart unless the product label says otherwise.
Why do antibiotics affect gut bacteria?
Antibiotics are designed to kill or suppress bacteria causing an infection, but they cannot fully distinguish between harmful bacteria and the beneficial bacteria that normally live in the gut. This disruption is one reason diarrhoea and digestive discomfort are common antibiotic side effects.
Health New Zealand includes probiotics among its list of supplements that some people find useful, and specifically calls out "a long course or repeated courses of antibiotics" as a situation where a probiotic may be worth considering — a more specific and evidence-aligned recommendation than a blanket claim about gut health.
What does the research actually show?
A systematic review and meta-analysis of randomised controlled trials (42 studies, over 11,000 participants) found that taking probiotics alongside antibiotics reduced the risk of antibiotic-associated diarrhoea in adults by around a third, with the overall evidence rated as moderate quality. Larger daily doses of the same probiotic tended to perform better than lower doses in subgroup analyses.
Importantly, the benefit was clearest in people who already had a moderate-to-high baseline risk of diarrhoea from their antibiotic course; the same reviews found little difference in lower-risk situations. This nuance is a good reminder that probiotics are not a guaranteed fix for everyone taking antibiotics.
Does it matter which probiotic and when you take it?
Research supporting probiotics for antibiotic-associated diarrhoea has generally used specific, well-studied strains (commonly from the Lactobacillus and Bifidobacterium groups, or the yeast Saccharomyces boulardii) at defined doses. This means results for one branded product do not automatically apply to a different product with different strains or a lower dose.
Because most antibiotics can also affect probiotic bacteria, many pharmacists suggest taking the two around two hours apart where practical. Saccharomyces boulardii is a yeast rather than a bacterium, so it is not affected by antibacterial antibiotics in the same way — check your specific product label for its own directions.
When should you speak to a pharmacist or GP instead?
A pharmacist can help you choose a probiotic product with reasonable evidence behind its strain and dose, and can flag interactions with your specific antibiotic. This matters more than picking whichever probiotic is on special.
- Severe, bloody or persistent diarrhoea during or after antibiotics
- You are immunocompromised, seriously unwell, or have a central line or feeding tube
- Symptoms in a young child, an older adult, or someone with a chronic health condition
- You are unsure whether your product contains a strain with actual evidence for this use
People also ask
Frequently asked questions
Should you take a probiotic during or after your antibiotic course?
Evidence generally supports starting a probiotic at the same time as, or soon after starting, the antibiotic, and continuing for at least the length of the course. Follow your product label or a pharmacist’s advice for your specific situation.
Are all probiotic supplements the same?
No. Strain, dose and the specific health outcome studied all matter. The research supporting probiotics for antibiotic-associated diarrhoea used particular strains and doses, so it should not be assumed every probiotic product on a shelf offers the same benefit.
Can children take a probiotic with antibiotics?
Probiotics have been studied in children for this purpose with a reasonable safety record in otherwise healthy children, but the right product, dose and suitability can vary. Check with a pharmacist, GP or paediatrician rather than assuming an adult product is appropriate.
Evidence and further reading
This guide provides general education, not diagnosis or individual medical advice. Follow product labels and speak with an appropriately qualified health professional when you are pregnant, nursing, taking medication or managing a health condition.
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