Yes, taking probiotics during a course of antibiotics is generally safe and can significantly reduce your risk of antibiotic-related side effects, especially diarrhea. A large meta-analysis published in BMJ Open found that taking probiotics alongside antibiotics reduces the risk of antibiotic-associated diarrhea in adults by 37%. The benefit is even stronger for people already at moderate or high risk of digestive side effects, where the reduction reaches 39% to 45%.
That said, timing matters, strain choice matters, and there are a few situations where probiotics can do more harm than good. Here’s what you need to know to get it right.
Why Antibiotics Cause Gut Problems
Antibiotics don’t distinguish between the bacteria making you sick and the beneficial bacteria living in your gut. A course of antibiotics can temporarily wipe out large portions of your gut microbiome, the diverse colony of microbes that helps you digest food, absorb nutrients, and keep harmful organisms in check. When that balance is disrupted, diarrhea, bloating, nausea, and cramping are common. In more serious cases, the disruption creates an opening for a harmful bacterium called C. difficile to take hold and cause a potentially dangerous infection.
Probiotics work by introducing live microorganisms that help fill the gap, competing with harmful bacteria for space and nutrients in your gut while your natural microbiome recovers.
How Much Probiotics Reduce Diarrhea Risk
The evidence is strongest for preventing antibiotic-associated diarrhea. Across pooled clinical trials, adults who took probiotics alongside antibiotics were 37% less likely to develop diarrhea than those who didn’t. Higher doses of the same probiotic pushed that number to a 46% reduction.
For people being treated for H. pylori infections (a common stomach bacteria that requires aggressive antibiotic therapy), probiotics reduced diarrhea as a side effect by 45%.
Probiotics also appear to protect against C. difficile infections specifically. A Cochrane review of 47 studies covering more than 15,000 participants found that probiotics reduced the risk of C. difficile-associated diarrhea by about 60%. Among people at highest baseline risk (greater than 5% chance of developing the infection), the reduction was 70%, with infection rates dropping from 11.6% in the control group to 3.1% in the probiotic group.
Which Probiotic Strains Work Best
Not all probiotics are equally suited for use during antibiotic treatment. Two stand out in the research:
- Saccharomyces boulardii: This is a yeast, not a bacterium, which gives it a unique advantage. Because antibiotics target bacteria, this yeast-based probiotic passes through your system completely unaffected by the antibiotic you’re taking. It reduces gut inflammation and has strong evidence for preventing both general antibiotic diarrhea and C. difficile infections.
- Lactobacillus rhamnosus GG: One of the most widely studied bacterial probiotic strains, with consistent evidence for reducing antibiotic side effects. Unlike S. boulardii, bacterial probiotics can be partially killed off by the antibiotic, which is why timing your doses matters (more on that below).
When choosing a product, look for the specific strain name on the label, not just the species. Different strains within the same species can have different effects. A product that lists only “Lactobacillus” or “Saccharomyces boulardii” without a strain identifier is less reliable than one that includes the full strain code.
Timing and Dosage
The most common recommendation is to stagger your probiotic dose 2 to 6 hours after each antibiotic dose. This gives the antibiotic time to reach peak concentration and begin clearing before you introduce live bacteria. Many practitioners suggest a 4 to 6 hour gap as the sweet spot.
If you’re using S. boulardii, timing is less critical since antibiotics don’t kill yeast. But staggering doses is still a reasonable habit to build into your routine.
For dosage, research suggests you need between 5 billion and 40 billion colony-forming units (CFU) per day to see a benefit during antibiotic treatment. Most effective study protocols used doses on the higher end of that range. Many over-the-counter probiotics fall in the 1 to 10 billion CFU range, so check the label and consider a higher-potency product specifically designed for antibiotic support.
When to Start and How Long to Continue
Start your probiotic on the same day you begin antibiotics. Most of the clinical trials showing benefit had participants taking both from day one. Continue the probiotic throughout your entire antibiotic course, then keep taking it for 7 to 10 days after your last antibiotic dose. This post-antibiotic window is important because your gut is still vulnerable to disruption even after the antibiotic clears your system.
Who Should Avoid Probiotics
For most healthy people on a standard course of antibiotics, probiotics are safe. Side effects, when they occur, are typically mild: a bit of extra gas or bloating in the first day or two.
There are important exceptions. People who are critically ill, severely immunocompromised, receiving nutrition through a feeding tube, or have a central venous catheter should not take probiotics, particularly S. boulardii. In these patients, the live yeast can enter the bloodstream and cause a serious fungal infection called fungemia. Healthcare workers’ hands can also transfer live yeast spores to catheter sites, compounding the risk. Ironically, hospitalized patients who might benefit most from C. difficile prevention are often the same patients for whom S. boulardii carries the greatest danger.
The Tricky Question of Long-Term Recovery
Here’s where the picture gets more complicated. While probiotics clearly help during antibiotic treatment, research from UCLA suggests that continuing probiotics for an extended period after finishing antibiotics may actually slow your gut’s full recovery. The reason: when your microbiome has been cleared out, the limited strains in a probiotic supplement can colonize the empty space and dominate. This can delay the return of the diverse, complex community of microbes that is unique to your body.
Your gut microbiome is resilient and will gradually recover over the course of several months. The practical takeaway is to use probiotics during and for about a week after your antibiotic course, but don’t feel you need to keep taking them indefinitely. After that initial recovery window, your gut is better served by a varied diet rich in fiber, fermented foods, and plant diversity, which feeds the return of your own native microbial community.