The two probiotics with the strongest evidence for recovery after antibiotics are Lactobacillus rhamnosus GG (often labeled LGG) and Saccharomyces boulardii, a beneficial yeast. Both have been shown to cut the risk of antibiotic-associated diarrhea roughly in half, and they work through different mechanisms, so choosing between them depends on your situation and what’s available.
What Antibiotics Do to Your Gut
Antibiotics kill the bacteria making you sick, but they also wipe out beneficial species in your intestines. Most people experience a sharp drop in the number of bacterial species living in their gut during and immediately after a course of antibiotics. For most healthy adults, species richness returns to roughly pre-treatment levels within about two months, but the composition isn’t the same. Even after the numbers bounce back, the balance of which species are present, what they produce, and how they function can remain altered for longer.
Some antibiotics hit harder than others. Azithromycin, for example, delays the recovery of species diversity and shifts gut composition more dramatically than many alternatives. And a subset of people experience a persistent reduction in microbiome diversity that doesn’t fully resolve on its own. This is the main reason probiotics are worth considering: they help fill the gap while your gut rebuilds, and they significantly reduce the most common side effect of that disruption, which is diarrhea.
The Best-Studied Strains
Not all probiotics are interchangeable. The strain matters enormously, and only a handful have strong clinical data behind them for antibiotic recovery specifically.
Lactobacillus rhamnosus GG (LGG) is the single most researched probiotic strain for antibiotic-associated diarrhea. In a meta-analysis of 12 trials covering nearly 1,500 people, LGG reduced the rate of antibiotic-associated diarrhea from about 22% to 12%. In children, doses of 10 to 20 billion CFU per day reduced diarrhea risk by 71%. You’ll find LGG sold under brand names like Culturelle, though it appears in other products too. Always check the label for the specific strain name.
Saccharomyces boulardii is a yeast, not a bacterium, which gives it one notable advantage: antibiotics don’t kill it. That means it survives in your gut even while you’re still taking your antibiotic course. It’s especially well studied for preventing diarrhea caused by Clostridioides difficile, a dangerous infection that can take hold when antibiotics clear out competing bacteria. The American Gastroenterological Association specifically suggests S. boulardii as one option for C. difficile prevention in people on antibiotics. You’ll find it sold under names like Florastor.
Beyond these two, the AGA also recognizes certain multi-strain combinations: a two-strain blend of L. acidophilus CL1285 and L. casei LBC80R, and a three- or four-strain combination that includes L. acidophilus, L. bulgaricus, Bifidobacterium bifidum, and sometimes Streptococcus thermophilus. These blends are found in products like Bio-K+. The evidence behind them is classified as low quality but conditionally supportive.
How Much to Take
Dose is just as important as strain. The most consistent results in clinical trials come from preparations delivering 5 to 40 billion CFU per day. Most probiotic supplements on the market fall in the 1 to 10 billion CFU range, so you may need to look specifically for higher-count products or take multiple doses. A European pediatric guidelines group recommends at least 5 billion CFU per day of either LGG or S. boulardii for children at risk of antibiotic-associated diarrhea.
Lower doses aren’t useless. Preparations under 5 billion CFU still showed benefit in trials, but you’d need to treat about 9 people to prevent one case of diarrhea, compared to roughly 6 people at higher doses. In practical terms, higher doses work faster and more reliably.
More is not automatically better, though. Going above 40 billion CFU hasn’t been shown to improve outcomes further, and there’s no evidence that “mega-dose” products with 100 billion CFU offer additional benefit for this specific purpose.
When to Start and How Long to Continue
The best time to start probiotics is on the same day you begin your antibiotic, not after you finish. Most clinical trials that showed benefit had participants taking probiotics alongside their antibiotics from day one. If you’re taking a bacterial probiotic like LGG, spacing your dose at least two hours away from your antibiotic gives the bacteria a better chance of surviving. S. boulardii doesn’t have this limitation since antibiotics don’t affect yeast.
Once you finish your antibiotic course, continue the probiotic for at least 7 to 14 days afterward. This is the dosing window tested in most studies. Given that gut diversity takes roughly two months to recover its baseline numbers, some people choose to continue longer, but the strongest evidence for preventing diarrhea and related complications covers that initial one- to two-week post-antibiotic window.
Fermented Foods vs. Supplements
Yogurt, kefir, sauerkraut, and kimchi all contain live microbes, but that doesn’t automatically make them probiotics. The International Scientific Association for Probiotics and Prebiotics draws a clear distinction: a true probiotic must contain live microbes defined to the strain level in amounts proven to deliver a health benefit. Most fermented foods don’t meet that bar. The bacteria in a jar of sauerkraut are varied and unquantified, and the strains in most commercial yogurts haven’t been tested for antibiotic recovery specifically.
That said, some yogurts and fermented milks do contain added probiotic strains listed on the label, and these can be a reasonable option if the strain and dose match what’s been studied. The key is checking the label for a specific strain name (like LGG, not just “Lactobacillus”) and a CFU count that meets the threshold through the “best by” date, not just at the time of manufacture. If the label doesn’t list a strain and a count, the product is a fermented food, not a clinically relevant probiotic.
Fermented foods are still worth eating during and after antibiotics. They provide a diverse set of live microbes and nutrients that support gut health broadly. They’re just not a reliable substitute for a targeted probiotic supplement if your goal is preventing diarrhea or supporting recovery from a specific antibiotic course.
Probiotics for Children After Antibiotics
Children are more susceptible to antibiotic-associated diarrhea than adults, and the evidence for probiotics in kids is actually stronger. In pediatric trials, the number needed to treat was 6, meaning for every 6 children given probiotics alongside antibiotics, one case of diarrhea was prevented. LGG and S. boulardii are the two strains with the most consistent pediatric data, at a dose of at least 5 billion CFU per day. Many children’s probiotic products contain these strains in age-appropriate formats like chewable tablets or powder sachets.
Who Should Be Cautious
Probiotics are safe for the vast majority of people, including children and older adults. The main exceptions are people with severely weakened immune systems, those with central venous catheters, and critically ill patients in intensive care. In these groups, live microbes (even beneficial ones) carry a small risk of entering the bloodstream and causing infection. S. boulardii in particular has been linked to rare cases of fungal bloodstream infections in hospitalized patients with central lines. If you’re immunocompromised or critically ill, probiotics are a conversation to have with your care team rather than something to start on your own.
For everyone else, the most common side effects are mild gas and bloating in the first few days, which typically resolve as your gut adjusts.