How Long After Taking Antibiotics Should I Take Probiotics?

Don't wait until the course is over. In the trials that cut antibiotic-associated diarrhoea, the live culture was started with the antibiotic, within the first two days, and taken daily to the end of the course. In 19 hospital studies, starting within two days of the first antibiotic dose cut C. difficile infection by about two-thirds (relative risk 0.32); starting later did not (0.70).¹ This page is one spoke of the Wellgard probiotics guide.

Evidence at a glance

• Trials: 42 adult trials, 11,305 people (2021); 33 children's trials, 6,352 (Cochrane 2019); 19 hospital studies, 6,261 (2017 timing analysis).
• Largest single trial: 2,981 UK inpatients aged 65 and over, one multistrain capsule daily for 21 days (PLACIDE, 2013).
• Strongest measured outcome: diarrhoea during antibiotics in children, 8% on live cultures against 19% on placebo (relative risk 0.45; nine children treated for one fewer case; moderate certainty).
• Not yet tested: no randomised trial has compared start days, stop days, or a gap of hours between the antibiotic and the capsule.

Sources checked on 16 October 2026.

How long after taking antibiotics should I take probiotics?

Hours, not days. The first dose of the culture belongs in the first day or two of the course, alongside the antibiotic rather than after it, because that is how the positive trials were designed. In a 2021 pooling of 36 placebo-controlled adult trials (9,312 people), diarrhoea was 38% less common on live cultures (relative risk 0.62, 0.51 to 0.74); the effect held whatever the reason for the antibiotic and whatever the gap between antibiotic and culture, and the authors' advice was to start "as early as possible".² A second 2021 pooling of 42 adult trials (11,305 people) put the reduction at 37% (moderate certainty), with no difference where the baseline risk of diarrhoea was low.³ In children, the 2019 Cochrane review of 33 trials (6,352) found diarrhoea in 8% on live cultures against 19% on placebo (relative risk 0.45; nine children treated for one fewer case; moderate certainty), and 5 billion CFU a day or more did better than less.⁴

What about the gap of two or three hours that many packs advise? No randomised trial has tested it; the pack's instruction is the pack's. The reasoning is that an antibacterial can kill a bacterial culture if the two arrive in the gut together. A laboratory model of the stomach and upper gut, run by a culture manufacturer on its own four-strain product, found the bacteria survived best taken with a meal or 30 minutes before one, and the yeast in the product was unaffected by meal timing.⁵ So: with a meal, a few hours from the antibiotic if the pack says so, every day of the course. Morning against night is on morning or night.

Should you take probiotics during or after a course of antibiotics?

During. The timing evidence points one way.

In the hospital studies, efficacy fell "for every day of delay in starting" (P = 0.04), and the gap between starting within two days (0.32) and later (0.70) was itself significant.¹ In over-65s, a 2022 pooling of eight trials (4,691 people) found the lower rate of diarrhoea only in trials that began within two days.⁶ One of the two late-start trials was the UK's PLACIDE: 2,981 inpatients aged 65 and over already on antibiotics, one multistrain lactobacillus-and-bifidobacterium capsule daily for 21 days, NIHR-funded. Diarrhoea occurred in 10.8% against 10.4% on placebo (relative risk 1.04) and C. difficile diarrhoea in 0.8% against 1.2% (0.71, not significant); no serious adverse event was attributed to the trial.⁷ A sceptical reader will quote PLACIDE, and should: it is the largest trial and it was null. It also started late, with one mixture.

Taking a culture only after the course, rather than alongside it, has been studied too, and the one study that did so points the other way. In a 2018 study that sampled the gut lining directly, healthy volunteers given a week of broad-spectrum antibiotics and then an 11-strain product showed a "markedly delayed and persistently incomplete" return of their own bacteria compared with people who took nothing.⁸ It is one invasive study of one product, its clinical meaning is unknown, and it is the reason this page does not say "repopulate afterwards".

Can you take probiotics and antibiotics at the same time?

Yes; that is what every positive trial did, and adverse events were no more common than on placebo (relative risk 1.00, 0.87 to 1.14).² Two kinds of culture behave differently. A bacterial culture can be killed by an antibacterial, which is the reason for the hours' gap. The yeast Saccharomyces boulardii is not: across 27 randomised trials in 5,029 adults, S. boulardii taken during antibiotic courses cut antibiotic-associated diarrhoea by about half (relative risk 0.47, 0.35 to 0.63).⁹ Strain decides the result in both cases; a mixture that worked in one trial is not evidence for a different one.

How long does it take for gut bacteria to recover after antibiotics?

No reliable figure exists, and the "six months" that circulates has no source we can find. Recovery varies with the antibiotic, the course and the person; the gut-lining study above measured it over weeks in healthy volunteers, and found it slower when an 11-strain culture was taken afterwards.⁸ The NHS says antibiotics "can have side effects such as diarrhoea and feeling sick", which "are usually mild and should pass once you finish your course of treatment" (page last reviewed 11 November 2022, past its review date).¹⁰ Diarrhoea that starts on a live culture itself is covered on can probiotics cause diarrhoea; thrush after antibiotics belongs to the women's health pages, starting with how to take women's probiotics.

Why don't doctors prescribe probiotics with antibiotics?

Because they are foods, not medicines, and guidance has not caught up with the trials. The NHS says probiotics "are generally classed as food rather than medicine, which means they don't go through the rigorous testing medicines do" and that "little is known about which types are best" (page last reviewed 24 November 2022, past its review date).¹¹ The timing analysis opens with the same point: reviews show a benefit, "but guidelines do not recommend probiotic use" for C. difficile.¹ The 2025 Cochrane update shows why. C. difficile diarrhoea fell from 3.2% to 1.6% (relative risk 0.50), an absolute difference of 1.6 percentage points, at low certainty because events are rare and some trials were never published; antibiotic-associated diarrhoea fell from 27.4% to 23% (0.67; low certainty); and 28 of the 47 trials had authors or funding from a culture company.¹²

What we don't know

• No randomised trial has compared start days or stop days; "within two days" comes from comparing trials with one another, not from a trial that randomised the start.
• No trial has tested the two-to-three-hour gap between antibiotic and capsule.
• Trials with a low baseline risk of diarrhoea found no difference, and no trial tells a healthy adult on a short course what their own risk is.

Frequently asked questions

Which comes first, antibiotic or probiotic?

The antibiotic, on its prescribed schedule, which never changes for a supplement. The culture starts the same day or the next, with a meal, a few hours from the antibiotic if the pack says so.^{1, 5}

How long should I keep taking them after the course?

The trials ran the culture for the course and, in several, beyond it; PLACIDE gave its capsule for 21 days.⁷ No trial has compared stopping dates, so finishing the pack you started is as evidence-based as any other rule.

Can I take them with nitrofurantoin or doxycycline?

The pooled trials covered antibiotics prescribed for every reason and the benefit held across them²; no trial singles out one antibiotic. Ask the pharmacist who dispenses it, and never move the antibiotic's own doses.

Do probiotics reduce antibiotic effectiveness?

No trial reports it. The concern runs the other way, the antibiotic killing a bacterial culture, which is why the yeast is the exception and the hours' gap exists.^{5, 9} The use-by-use evidence is on do probiotics work.

Sources

1. Shen NT, et al. Gastroenterology, 2017 (timing of live cultures and C. difficile infection in hospital adults). Systematic review with meta-regression, 19 studies, 6,261 people. PubMed 28192108.
2. Liao W, et al. Probiotics for the Prevention of Antibiotic-associated Diarrhea in Adults: A Meta-Analysis of Randomized Placebo-Controlled Trials. Journal of Clinical Gastroenterology, 2021. Pooled analysis of 36 randomised trials, 9,312 adults. PubMed 33234881.
3. Goodman C, et al. Probiotics for the prevention of antibiotic-associated diarrhoea: a systematic review and meta-analysis. BMJ Open, 2021. Pooled analysis of 42 randomised trials, 11,305 adults. PubMed 34385227.
4. Guo Q, et al. Probiotics for the prevention of pediatric antibiotic-associated diarrhea. Cochrane Database of Systematic Reviews, 2019. Cochrane review, 33 randomised trials, 6,352 children. PubMed 31039287.
5. Tompkins TA, Mainville I, Arcand Y. The impact of meals on a probiotic during transit through a model of the human upper gastrointestinal tract. Beneficial Microbes, 2011. Laboratory model, no participants; run by a culture manufacturer on its own product. PubMed 22146689.
6. Zhang L, et al. Early use of probiotics might prevent antibiotic-associated diarrhea in elderly (>65 years): a systematic review and meta-analysis. BMC Geriatrics, 2022. Pooled analysis of 8 randomised trials, 4,691 people. PubMed 35794520.
7. Allen SJ, et al. Lactobacilli and bifidobacteria in the prevention of antibiotic-associated diarrhoea and Clostridium difficile diarrhoea in older inpatients (PLACIDE): a randomised, double-blind, placebo-controlled, multicentre trial. Lancet, 2013. Randomised trial, 2,981 inpatients aged 65 and over, 21 days; NIHR-funded. PubMed 23932219.
8. Suez J, et al. Post-Antibiotic Gut Mucosal Microbiome Reconstitution Is Impaired by Probiotics and Improved by Autologous FMT. Cell, 2018. Invasive sampling study in healthy volunteers (number not in the abstract). PubMed 30193113.
9. McFarland LV. Systematic review and meta-analysis of Saccharomyces boulardii in adult patients. World Journal of Gastroenterology, 2010. Pooled analysis of 27 randomised trials, 5,029 people. PubMed 20458757.
10. NHS. Antibiotics: side effects. nhs.uk. Page last reviewed 11 November 2022 (review overdue).
11. NHS. Probiotics. nhs.uk. Page last reviewed 24 November 2022 (review overdue).
12. Esmaeilinezhad Z, et al. Probiotics for the prevention of Clostridioides difficile-associated diarrhea in adults and children. Cochrane Database of Systematic Reviews, 2025. Cochrane review, 47 randomised trials, 15,260 people. PubMed 40931979.

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