The two probiotics with the strongest evidence for use alongside antibiotics are Saccharomyces boulardii (a beneficial yeast) and Lactobacillus rhamnosus GG (often labeled as LGG). Both have been tested across multiple clinical trials and shown to roughly cut the risk of antibiotic-associated diarrhea in half. Your best choice between them depends on a few factors, including what’s available to you and whether you’re choosing for a child or an adult.
Why Antibiotics Disrupt Your Gut
Antibiotics don’t selectively kill only the bacteria making you sick. They also wipe out beneficial species that help you digest food, produce nutrients, and keep harmful microbes in check. Research published in Frontiers in Microbiology found that a course of antibiotics significantly reduced key bacterial populations, including species responsible for producing short-chain fatty acids, the compounds that fuel the cells lining your colon and help regulate inflammation.
The disruption isn’t brief. After a longer course of antibiotics, measurable changes in gut bacterial diversity persisted for eight months or more. Even after a shorter course, full recovery took many months. This explains why some people experience digestive issues well beyond the last pill. Starting a probiotic early and continuing it after your antibiotic course is one of the most practical steps you can take to reduce that window of disruption.
Saccharomyces Boulardii: The Strongest Overall Pick
S. boulardii is a yeast, not a bacterium, which gives it a built-in advantage: antibiotics designed to kill bacteria don’t touch it. That means it survives in your gut even while you’re actively taking your prescription. A meta-analysis of 21 randomized controlled trials covering nearly 4,800 participants found that S. boulardii cut the rate of antibiotic-associated diarrhea from 18.7% down to 8.5%, roughly halving the risk in both children and adults.
S. boulardii also showed particular promise against C. difficile, a dangerous gut infection that can take hold when antibiotics clear the way. Across broader reviews, probiotics containing S. boulardii reduced C. difficile-associated diarrhea by about 58.5%. The American Gastroenterological Association specifically names S. boulardii among the strains with evidence supporting use for C. difficile prevention during antibiotic therapy.
Look for products listing “Saccharomyces boulardii” on the label with a minimum daily dose of 10 billion CFU. Common brand names include Florastor, though store-brand equivalents containing the same strain work too.
Lactobacillus Rhamnosus GG (LGG)
LGG is the most studied bacterial probiotic strain in the world and carries solid evidence for antibiotic support, especially in children. A meta-analysis of 12 randomized trials found it reduced antibiotic-associated diarrhea from 22.4% to 12.3% overall. In children specifically, the benefit was statistically significant. In adults, the results trended positive but were strongest in people taking antibiotics for H. pylori treatment, where LGG cut diarrhea risk by about 74%.
Because LGG is a bacterium, some of it will be killed by your antibiotic. Spacing doses (more on timing below) helps, but this is one reason S. boulardii edges ahead as a general recommendation. Still, LGG earns the highest evidence rating in practical dosing guides, with a recommended minimum of 2 billion CFU per day. It’s widely available under brands like Culturelle.
Single Strain vs. Multi-Strain Formulas
Pharmacy shelves are full of multi-strain products advertising 10 or 15 different species, which can feel like a better deal. The evidence doesn’t clearly support that logic. A 2020 meta-analysis of 65 randomized trials found single-strain probiotics were generally equivalent to multi-strain mixtures. In some cases, strains in a multi-strain product can actually compete with or inhibit each other, a phenomenon researchers call “mutual antagonism.”
Multi-strain formulas did show advantages in a few specific contexts, like preventing a serious intestinal condition in premature infants. But for the straightforward goal of preventing diarrhea during an antibiotic course, a well-studied single strain at the right dose is a reliable choice. If you do choose a multi-strain product, check that it contains at least one of the strains with strong clinical evidence rather than a scattershot list of untested species.
How Much to Take
Dose matters. Research shows that a daily intake of at least 5 billion CFU is associated with meaningful protection against antibiotic-associated diarrhea, and higher doses tend to work better. For specific strains, the minimum effective doses identified in clinical reviews are:
- Saccharomyces boulardii: 10 billion CFU per day
- Lactobacillus rhamnosus GG: 2 billion CFU per day
Many over-the-counter products contain 5 to 15 billion CFU per capsule, which falls within the effective range. Some products advertise 50 billion or more; there’s no strong evidence that mega-doses provide additional benefit for this specific purpose, though they aren’t harmful for most people.
When to Start and How Long to Continue
Start your probiotic as soon as possible after beginning antibiotics, ideally the same day. The International Scientific Association for Probiotics and Prebiotics recommends continuing the probiotic for at least one week after your antibiotic course ends, with many clinical protocols testing a 7 to 14 day post-antibiotic window. Given that gut recovery can take months, continuing for two weeks after your last antibiotic dose is a reasonable approach.
If you’re taking a bacterial probiotic like LGG, spacing it a few hours from your antibiotic dose makes sense so the antibiotic doesn’t immediately destroy the probiotic bacteria in your stomach. Taking the probiotic with a meal at the opposite end of the day from your antibiotic is a practical strategy. With S. boulardii, timing is less critical since antibacterial drugs don’t affect yeast, but taking it with food still helps.
Who Should Be Cautious
Probiotics are safe for the vast majority of people, but there are exceptions. The CDC has documented cases of S. boulardii entering the bloodstream in critically ill patients, particularly those receiving nutrition through a feeding tube or who have a central venous catheter. People with severely weakened immune systems, such as those undergoing chemotherapy or organ transplant recipients on immunosuppressive drugs, should talk with their care team before starting any probiotic.
For otherwise healthy people taking a standard course of antibiotics for a common infection, probiotics carry minimal risk and measurable benefit. The number needed to treat with S. boulardii is 10, meaning for every 10 people who take it alongside antibiotics, one case of diarrhea is prevented that would have otherwise occurred. That’s a strong return for an inexpensive supplement with very few side effects.