Short answer: in healthy adults, the gut microbiome usually recovers most of its makeup on its own within weeks to a couple of months after a course of antibiotics, though some species may not come back. No food or supplement has been shown to “reset” it faster – and in one trial, probiotics taken after antibiotics actually slowed recovery. Eat a varied, plant-rich diet with fermented foods you enjoy, take your antibiotics exactly as prescribed, and contact a doctor if you get diarrhoea during or after the course.
What Antibiotics Do to the Gut
A detailed study followed three people’s gut bacteria for ten months across two courses of ciprofloxacin. Diversity fell within 3–4 days of starting each course; communities began returning about a week after it ended, but the return was often incomplete, and each person ended up in a slightly different stable state (Dethlefsen & Relman, 2011). In a larger study, 12 healthy men took a four-day course of three strong antibiotics. Their gut microbiota recovered to near its original composition within about six weeks, but nine common species that all of them carried beforehand were still undetectable in most of them six months later (Palleja et al., 2018). The picture: a real disruption, substantial natural recovery, and some lasting changes that vary from person to person.
Probiotics: Prevention Is Not the Same as Recovery
Two questions often get mixed up. Can probiotics taken with antibiotics prevent diarrhoea? For some strains, yes: Cochrane reviews found fewer cases of antibiotic-associated diarrhoea in children (Guo et al., 2019) and of C. difficile diarrhoea in people at high risk (Goldenberg et al., 2017), and the American Gastroenterological Association conditionally suggests certain specific strains to prevent C. difficile during antibiotic treatment (Su et al., 2020). Ask your doctor or pharmacist which, if any, suits you – see our guide to probiotic supplements.
Do probiotics help the gut microbiome recover afterwards? The evidence points the other way. In a trial in which healthy volunteers took antibiotics, those then given a multi-strain probiotic had a markedly delayed and persistently incomplete return of their own gut and gut-lining microbiome, compared with people left to recover on their own (Suez et al., 2018). It’s one trial, with one product, but it’s a reason not to assume that “more bacteria” means faster recovery.
What to Eat
- A wide variety of plants. In the American Gut citizen-science project, people who reported eating more than 30 different plant types a week had more diverse gut microbiota than those eating fewer than 10 (McDonald et al., 2018). That’s an observational comparison of small groups, not proof of cause, but a varied diet of vegetables, fruit, whole grains, legumes, nuts, seeds, herbs and spices is sound advice anyway.
- Fermented foods you enjoy. In a small Stanford trial, a diet high in fermented foods increased microbiota diversity and lowered markers of inflammation in healthy adults (Wastyk et al., 2021). It wasn’t a study of people recovering from antibiotics, so think of yogurt, kefir, sauerkraut or kimchi as good food, not treatment (see how much fermented food per day).
- Go gently if your gut is upset. If you have loose stools or bloating, simple foods and plenty of fluids come first; add fibre-rich foods back gradually.
When to Call a Doctor
Most cases of C. difficile infection happen during or shortly after antibiotic use: people are up to 10 times more likely to get it while taking antibiotics and in the month afterwards. Symptoms include diarrhoea, fever, abdominal pain or tenderness, loss of appetite and nausea. If you get diarrhoea while taking or after taking an antibiotic, contact a healthcare professional to be evaluated (CDC). Don’t stop a prescribed antibiotic early without medical advice, and don’t take leftover antibiotics.
For more on what affects live cultures, see what kills probiotics.
