You finish the course. The last capsule goes down with a glass of water, the infection's gone, and your gut feels a little… off. Looser. Grumbly. Somewhere between fine and not quite right. So you reach for a probiotic, because that's what everyone says you should do.
Is it the right move? Sometimes. The timing matters more than most labels let on, the strain matters more than the number on the front, and one well-known study suggests that for some people, waiting might work just as well. Here's what the research shows.
What antibiotics actually do to your gut
Antibiotics are blunt instruments by design. They're meant to knock out the bacteria making you ill, but they can't tell those apart from the trillions of microbes quietly living in your gut. Broad-spectrum courses in particular thin out the whole community for a while.
For most people the effect is mild and temporary. For a minority, it shows up as antibiotic-associated diarrhoea, usually within the first few days of a course. In rarer, more serious cases (mostly in hospital, mostly in older people) it opens the door to Clostridioides difficile, a bacterium that thrives when the usual competition has been cleared out.
That's the gap probiotics are supposed to fill. The NHS describes them as "thought to help restore the natural balance of bacteria" when it's been disrupted by illness or treatment, while noting there's little evidence behind many of the wider claims made about them.[1]
The evidence for taking probiotics with antibiotics
This is one of the better-studied areas in the whole probiotic field, and on balance the research leans positive.
A 2012 meta-analysis in JAMA pooled 63 randomised trials with nearly 12,000 participants and found that taking probiotics alongside antibiotics was associated with a 42% lower relative risk of antibiotic-associated diarrhoea.[2] In children, a 2019 Cochrane review of 33 studies found a moderate protective effect, strongest at higher doses of 5 billion CFU a day or more.[3]
But "probiotics" isn't one thing, and the results aren't uniform. The largest single trial in this area, PLACIDE, published in The Lancet in 2013, gave nearly 3,000 older hospital patients either a multi-strain mix (including Lactobacillus acidophilus and two bifidobacteria) or a placebo. Diarrhoea rates came out almost identical: 10.8% versus 10.4%.[4]
So the fair summary is this. Across many trials, probiotics look helpful on average. That average hides a lot of variation by strain, dose, and who's taking them, and the strongest results tend to come from specific named strains at doses higher than many shop-shelf products contain.
Timing: during the course, or after?
Most of the positive trials started probiotics during the antibiotic course, not after it. One analysis makes the point especially clearly.
A 2017 meta-analysis in Gastroenterology looked at 19 trials in hospitalised adults and found probiotics were more effective the closer they were started to the first antibiotic dose, losing some effect with each day of delay.[5]
Two caveats. That finding is about C. difficile in hospital patients, not everyday tummy upset after a course for a chest infection. And it tells you about starting early, not about the hour-by-hour gap between doses.
On that gap: the usual advice is to leave a couple of hours between your antibiotic and your probiotic, so the antibiotic has less chance of hitting the live cultures straight away. It's sensible and harmless, but it's a convention rather than something trials have tested head-to-head. Your pharmacist can tell you whether it matters for your specific antibiotic, and some (certain antibiotics bind to minerals, for instance) have their own timing rules worth asking about.
The study that complicates things
In 2018, a team at the Weizmann Institute published a study in Cell that got a lot of attention. After a course of antibiotics, a small group of healthy volunteers either took an 11-strain probiotic, received a transplant of their own pre-antibiotic gut bacteria, or did nothing.[6]
The surprise: the probiotic group's gut microbiome took longer to return to its original state than the do-nothing group. The probiotic strains settled in and seemed to slow the regrowth of the person's native bacteria.
It was a small study, it measured microbiome composition rather than symptoms, and it hasn't overturned the trial evidence on diarrhoea. But it's a useful reminder that "restoring balance" isn't as simple as topping the gut back up. Your own microbes usually return on their own given time and a decent diet. Probiotics may ease the transition for some people. They aren't a reset button.
"Probiotics may ease the transition for some people. They aren't a reset button."
A sensible approach, in practice
Pulling it together, here's how we'd think about it:
- Start early if you're going to start at all — most of the supportive research begins probiotics during the course, not after it ends.
- Space the doses — a couple of hours either side of your antibiotic is a reasonable habit, and worth checking with your pharmacist.
- Feed your own bacteria too — fibre from vegetables, oats, beans and fermented foods gives your native microbes something to regrow on. (Our piece on probiotics vs prebiotics explains why both matter.)
- Keep going for a few weeks — rather than stopping the day the antibiotics finish.
If you'd rather keep things simple, a single daily tablet that slots into the routine you already have is easier to stick with than anything elaborate. That's the thinking behind Daily Pro Bio Cultures: one mini tablet of Lactobacillus acidophilus, 550 million live cultures, vegan, four months to a tub. To be clear about what it is, it's a gentle everyday option, not a replica of the higher-dose, strain-specific formulas used in the antibiotic trials above, and those study results shouldn't be read as applying directly to it.
When to skip the supplement and call your GP
Mild, short-lived loose stools during a course are common. Diarrhoea that's severe, bloody, comes with a fever or stomach cramps, or keeps going after you've stopped the antibiotics is a different matter, and needs a GP or NHS 111, not a probiotic. The same goes for anyone with a weakened immune system or a serious underlying condition: the NHS advises talking to a doctor before taking probiotic supplements at all.[1]
The quiet part of recovery
Most guts come back. Slowly, unglamorously, helped along by sleep, fibre, water and a bit of patience. A probiotic can be a reasonable part of that, especially started early. Just choose one you'll actually take every day, keep your expectations honest, and give your own bacteria the credit they're due.
Frequently asked questions
Should I take probiotics during or after antibiotics?
Most of the trials that found a benefit started probiotics during the antibiotic course, and a 2017 meta-analysis found the effect against C. difficile was strongest when probiotics began within two days of the first antibiotic dose. Many people carry on for a few weeks after the course ends too.
How many hours apart should I take probiotics and antibiotics?
A gap of around two hours is the usual advice, so the antibiotic has less chance of affecting the live cultures directly. It's a practical convention rather than a trial-tested rule, so check with your pharmacist, particularly if your antibiotic has its own instructions about food or minerals.
How long does it take for gut bacteria to recover after antibiotics?
It varies from person to person and by antibiotic. In a small 2018 study published in Cell, healthy volunteers who took nothing after antibiotics saw their gut bacteria drift back towards their original mix on their own, while those given a probiotic took longer to get there. For a broader look at timelines, see our guide on how long probiotics take to work.
Can probiotics stop antibiotics from working?
There's no good evidence that probiotics reduce how well antibiotics treat an infection; probiotics act on gut bacteria, not on the infection itself. Antibiotics can kill probiotic bacteria, though, which is one reason people space the doses apart. Always finish your course as prescribed.
Sources
- NHS — Probiotics: what they're thought to do, evidence limits, and advice for people with weakened immune systems. https://www.nhs.uk/tests-and-treatments/probiotics/
- Hempel S. et al. (2012), JAMA — meta-analysis of 63 RCTs (11,811 participants); probiotics associated with reduced antibiotic-associated diarrhoea (RR 0.58). https://jamanetwork.com/journals/jama/fullarticle/1151505
- Guo Q. et al. (2019), Cochrane Database of Systematic Reviews CD004827 — probiotics for preventing antibiotic-associated diarrhoea in children; strongest effect at ≥5 billion CFU/day. https://www.cochrane.org/evidence/CD004827_probiotics-prevention-antibiotic-associated-diarrhea-children
- Allen S.J. et al. (2013), The Lancet — PLACIDE trial; multi-strain lactobacilli and bifidobacteria showed no reduction in antibiotic-associated diarrhoea in older inpatients (10.8% vs 10.4%). https://www.thelancet.com/article/S0140-6736(13)61218-0/fulltext
- Shen N.T. et al. (2017), Gastroenterology — meta-regression of 19 trials; probiotics more effective against C. difficile when started within 2 days of antibiotics. https://pubmed.ncbi.nlm.nih.gov/28192108/
- Suez J. et al. (2018), Cell — post-antibiotic microbiome recovery delayed by an 11-strain probiotic compared with no intervention. https://pubmed.ncbi.nlm.nih.gov/30193113/
At Oxford Origins, your wellbeing is our priority, and although we pride ourselves on our expertise in nutrition and supplementation, it's important to acknowledge the individuality of each person. Articles published by Oxford Origins are not intended to treat, diagnose, cure or prevent any disease, or replace the advice of your GP. We always recommend consulting with a healthcare provider if you encounter any health concerns, and we'll always be here to support you so you're never alone on your journey.
