Gut health after antibiotics: what actually helps, and what’s the wrong way round

If you’re on antibiotics this winter, or you’ve just finished a course and your gut hasn’t felt right since, this is for you. Gut health after antibiotics is one of the most common things I’m asked about, and most of the standard advice has the timing back to front.

The short version: take the antibiotic exactly as prescribed. If you want a probiotic, the best evidence is for one specific yeast, Saccharomyces boulardii, taken during the course. Once you’ve finished, food does more of the rebuilding than capsules do. Most people’s gut bacteria settle within about six weeks, but not all of them.

What most people get wrong

The usual plan goes like this: get through the antibiotics, then take a high-strength, multi-strain probiotic for a month to “repopulate” the gut.

It sounds logical. The evidence points the other way on both counts.

First, the period when a probiotic has the clearest benefit is while you’re taking the antibiotic, not afterwards. That’s when antibiotic-associated diarrhoea happens, and that’s what the trials measured.

Second, a bacterial probiotic straight after a course may not help your own bacteria come back. In a 2018 study from the Weizmann Institute, volunteers who took an 11-strain probiotic after antibiotics took longer to return to their original gut bacteria than people who took nothing, and some still hadn’t after five months (Suez et al., 2018). It was a small study using one product, and it measured bacteria rather than symptoms, so I wouldn’t overstate it. But it should give anyone pause before taking a probiotic by default.

What antibiotics actually do to your gut

Antibiotics can’t tell the bacteria causing your chest infection from the ones in your bowel. Within a few days of starting a course, the number of species in your gut drops sharply.

In a Danish study, 12 healthy men were given a four-day course of three strong antibiotics. Their gut bacteria were back near baseline by about six weeks. But nine common species that everyone had at the start were still undetectable in most of them six months later (Palleja et al., 2018).

The antibiotic you’re given matters. A 2026 Swedish study of almost 15,000 adults linked some antibiotic classes, mainly clindamycin, fluoroquinolones (such as ciprofloxacin) and flucloxacillin, to measurable differences in gut bacteria four to eight years later. Penicillin V, the most common first-line antibiotic there, was linked only to small, short-lived changes (Baldanzi et al., 2026). That’s an association, not proof of cause, but it explains why one course can leave some people’s digestion different for months while others notice nothing.

What happens during recovery depends heavily on what your gut bacteria are fed. In a 2025 study in mice, the ones eating a high-fibre diet after antibiotics had largely recovered within two weeks. The ones on a low-fibre Western-style diet were still disrupted at nine weeks. A faecal transplant didn’t make up the difference without the right diet (Kennedy et al., 2025). That was in mice, but it fits what I see in clinic: in the weeks after antibiotics, what you eat matters more than which supplement you buy.

How to look after your gut during and after antibiotics

During the course

1. Take the antibiotic exactly as prescribed, to the end. Don’t stop or space doses to protect your gut. If side effects are bad, speak to your GP or pharmacist, because they may be able to switch you to a different antibiotic.
2. Consider Saccharomyces boulardii from day one. It’s a yeast, so antibacterial antibiotics don’t kill it and you don’t need to time it around your doses. Across 21 trials, it cut the rate of antibiotic-associated diarrhoea from about 19% to 8.5% (Szajewska and Kołodziej, 2015). Most trials used around 250 to 1,000 mg a day. Carry on for a few days after your last antibiotic dose. Skip it if you’re immunocompromised, critically ill or have a central line, and check with your GP first if you’re on an antifungal, since antifungals kill it.
3. If you use a bacterial probiotic instead, space it two hours from the antibiotic. Otherwise the antibiotic simply kills it.
4. Read the leaflet for food rules. Doxycycline and ciprofloxacin, for example, bind to calcium, so milk, yoghurt and calcium supplements need to be kept apart from your doses. With metronidazole, there’s no alcohol during the course or for 48 hours afterwards. That’s worth knowing with party season coming up.
5. Keep eating fibre if you can tolerate it. If you have diarrhoea, softer options such as oats, banana, rice, cooked carrots and well-cooked lentils still feed your gut bacteria without being harsh on it.

After the course

1. Feed your gut bacteria, don’t just add new ones. Aim for 30 different plants a week: vegetables, fruit, whole grains, pulses, nuts, seeds, herbs and spices all count. People who eat that many plants have more varied gut bacteria than people who eat ten or fewer (McDonald et al., 2018).
2. Add fermented foods gradually. Kefir, live yoghurt, sauerkraut and kimchi, a small portion a day. In a ten-week Stanford trial, a diet high in fermented foods increased gut bacteria diversity (Wastyk et al., 2021).
3. Increase fibre slowly. Increase it over a fortnight rather than overnight. If more fibre makes you noticeably bloated, that tells you something useful (see below).
4. Don’t take a bacterial probiotic by default afterwards. Some people do benefit, but it’s worth having a reason rather than taking one just in case.
5. Give it six to eight weeks, and keep notes. Track stool form, bloating and energy. If things are steadily improving, keep going. If they’ve stalled, that’s useful information too.

When it’s the GP, not me

The main risk after antibiotics is C. difficile, a bacterial infection that can take hold when your usual gut bacteria are knocked back. The risk lasts for several weeks after the course ends. Speak to your GP or call 111 the same day if you have frequent watery diarrhoea during or after antibiotics, especially with a fever, stomach cramps or blood.

Also see your GP for blood in your stool, unexplained weight loss, symptoms that wake you at night, difficulty swallowing, a new change in bowel habit after 50, or a family history of bowel cancer, coeliac disease or IBD.

Frequently asked questions

Should I take probiotics with antibiotics?

The best evidence is for Saccharomyces boulardii taken during the course, to reduce the risk of antibiotic-associated diarrhoea. Probiotics as a group also lowered the risk of C. difficile diarrhoea in a Cochrane review, from about 4% to 1.5% (Goldenberg et al., 2017).

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

For most people, the main groups of gut bacteria are back near baseline in about six weeks. Some individual species can take six months or longer, and certain antibiotics have been linked to differences years later.

Why am I bloated after antibiotics?

With fewer of your usual bacteria, the ones that are left, including gas-producing species, have less competition. For most people it settles within a few weeks. If it’s still there after two months, or gets worse when you eat more fibre, it’s worth looking into properly, sometimes with a breath test or stool test.

What should I eat after antibiotics?

A wide range of plants, some fermented foods, and enough fibre, built up gradually. Oats, pulses, cooled potatoes and rice, onions, leeks, apples and kefir are good places to start.

If your gut hasn’t settled

Most people bounce back. The ones I see are the people who don’t: the bloating started with “that course of antibiotics in the spring” and never really went away, or every attempt to eat more vegetables makes things worse. That’s not something you just have to put up with. It’s usually a pattern we can identify, sometimes with testing, and then work on in a set order. If that sounds familiar, book a free 30-minute call and we’ll talk through whether it’s worth looking into.

References

• Baldanzi G et al. (2026). Antibiotic use and gut microbiome composition links from individual-level prescription data of 14,979 individuals. Nature Medicine 32(4):1351–1361.
• Goldenberg JZ et al. (2017). Probiotics for the prevention of Clostridium difficile-associated diarrhea in adults and children. Cochrane Database of Systematic Reviews CD006095.
• Kennedy MS et al. (2025). Diet outperforms microbial transplant to drive microbiome recovery in mice. Nature 642:747–755.
• McDonald D et al. (2018). American Gut: an open platform for citizen science microbiome research. mSystems 3(3):e00031-18.
• Palleja A et al. (2018). Recovery of gut microbiota of healthy adults following antibiotic exposure. Nature Microbiology 3:1255–1265.
• Suez J et al. (2018). Post-antibiotic gut mucosal microbiome reconstitution is impaired by probiotics and improved by autologous FMT. Cell 174(6):1406–1423.
• Szajewska H, Kołodziej M (2015). Systematic review with meta-analysis: Saccharomyces boulardii in the prevention of antibiotic-associated diarrhoea. Alimentary Pharmacology & Therapeutics 42(7):793–801.
• Wastyk HC et al. (2021). Gut-microbiota-targeted diets modulate human immune status. Cell 184(16):4137–4153.e14.