Researchers looked at 47 studies involving over 15,000 people to see if probiotics (good bacteria supplements) could prevent a serious type of diarrhea caused by antibiotics. They found that probiotics may help reduce the risk of this infection by about half, meaning roughly 1 in 65 people taking probiotics might avoid getting sick. The good news is that probiotics appear safe with few side effects. However, the benefit is small, and more research is needed to confirm these results, especially in people with lower risk of getting this infection.

The Quick Take

  • What they studied: Whether taking probiotic supplements (live good bacteria) while on antibiotics can prevent a serious type of diarrhea caused by a harmful bacteria called C. difficile
  • Who participated: 47 different studies with a total of 15,260 adults and children who were taking antibiotics for various reasons
  • Key finding: Probiotics reduced the risk of getting C. difficile diarrhea by about 50%, dropping the chance from 3.2% to 1.6%. This means for every 65 people taking probiotics, one person might avoid getting this infection
  • What it means for you: If you’re taking antibiotics, probiotics may offer modest protection against antibiotic-related diarrhea and appear to be safe. However, the benefit is small, and you should talk to your doctor before starting any supplement, especially if you have a weakened immune system

The Research Details

This was a systematic review, which means researchers searched through all available high-quality studies on this topic and combined their results. They looked at 47 randomized controlled trials (the gold standard type of study) published between 2017 and 2025. In these trials, some people received probiotics while others received a placebo (fake pill) or no treatment, and researchers tracked who developed C. difficile diarrhea.

The researchers carefully checked each study for quality issues, like whether people were randomly assigned to groups fairly and whether results were reported honestly. They also looked at different types of probiotics, different doses, and different groups of people (adults versus children, hospital patients versus outpatients) to see if results varied.

They used a method called GRADE to rate how confident they should be in their findings. This helps readers understand whether the results are solid or if there’s still a lot of uncertainty.

This research approach is important because C. difficile diarrhea is a serious problem that can happen when antibiotics kill off the good bacteria in your gut. By combining results from many studies, researchers can see the bigger picture and determine if probiotics really work, rather than relying on just one study that might have been lucky or unlucky. The systematic review approach also helps identify problems, like studies funded by probiotic companies that might be biased.

The review found some concerns worth knowing about: about 30% of studies didn’t register their plans ahead of time (which can lead to reporting only positive results), and 28 studies received money from probiotic companies (which might bias results in favor of probiotics). However, the researchers found that these issues didn’t significantly change the main findings. The studies varied quite a bit in their results, which suggests that probiotics may work better in some situations than others. The certainty of evidence was rated as moderate, meaning the findings are fairly reliable but not perfect.

What the Results Show

The main finding was that probiotics reduced the risk of developing C. difficile diarrhea by about half compared to placebo or no treatment. In the probiotic group, 1.6% of people developed the infection, compared to 3.2% in the control group. This translates to a relative risk reduction of 50%, which sounds impressive, but the absolute difference is small—only 1.6 percentage points.

To put this in practical terms, you would need to give probiotics to 65 people to prevent one case of C. difficile diarrhea. This is called the “number needed to treat.” The researchers were fairly confident in this finding, rating it as moderate certainty evidence.

The researchers also found that probiotics appeared to be safe. There were probably fewer adverse events (side effects) in the probiotic group compared to the control group, though the evidence for this was less certain. No serious safety concerns were identified in the studies reviewed.

The review looked at several other outcomes beyond just preventing C. difficile diarrhea. They examined whether probiotics could prevent general antibiotic-associated diarrhea (any diarrhea from antibiotics, not just from C. difficile), and found similar modest benefits. The researchers also looked at hospital stay length but found the evidence was too inconsistent to draw firm conclusions. They noted that detecting C. difficile bacteria in stool without symptoms didn’t necessarily predict who would get sick, so this wasn’t a reliable measure of benefit.

This is an update of a review first done in 2013, with the most recent update in 2017. The new version added 8 additional studies with nearly 4,600 more participants. The overall conclusion remains similar to previous versions: probiotics may offer modest protection, but the benefit is small. The updated review confirms that probiotics are generally safe, which is reassuring. However, the researchers note that more large, high-quality studies are still needed, particularly in people with lower baseline risk of developing C. difficile diarrhea.

Several important limitations should be considered. First, many studies were funded by probiotic companies, which could bias results in favor of probiotics. Second, about 30% of studies didn’t pre-register their methods, meaning researchers might have changed their plans after seeing results. Third, the studies used many different probiotic strains and doses, making it hard to know which specific probiotics work best. Fourth, most studies were done in hospital settings with higher-risk patients, so results might not apply to healthy people taking antibiotics at home. Finally, the benefit is small in absolute terms, so for most people, the practical impact may be limited.

The Bottom Line

Based on moderate certainty evidence, probiotics may be considered as a preventive measure for people taking antibiotics who are at higher risk for C. difficile infection (such as hospitalized patients or elderly people). However, the benefit is modest—preventing one case for every 65 people treated. Probiotics appear safe with few side effects. If you’re considering probiotics, discuss it with your doctor first, especially if you have a weakened immune system, are critically ill, or have other health conditions. Probiotics should not replace standard infection control measures like hand washing.

This research is most relevant for hospitalized patients taking antibiotics, elderly people on antibiotics, and people with conditions that weaken their immune system. People taking antibiotics at home for routine infections may have lower risk and might not benefit as much. People who are critically ill or severely immunocompromised should talk to their doctor before taking probiotics, as the safety evidence in these groups is limited. Healthy people taking short courses of antibiotics for minor infections probably have low enough risk that probiotics offer minimal benefit.

If probiotics are going to help, the benefit would likely appear during the time you’re taking antibiotics and for a few weeks afterward, since C. difficile diarrhea typically develops during or shortly after antibiotic use. You wouldn’t expect to see benefits weeks or months later. Most studies looked at short-term use (during and shortly after antibiotics), so we don’t know if long-term probiotic use offers additional benefits.

Want to Apply This Research?

  • If taking probiotics during antibiotic treatment, track daily bowel movements and stool consistency using a simple 1-5 scale (1=hard, 5=watery). Note any cramping, fever, or blood in stool. This helps identify problems early and provides data to discuss with your doctor.
  • Set a daily reminder to take your probiotic at the same time each day, preferably with food. Start taking it on the first day of antibiotics and continue for at least one week after finishing antibiotics. Keep a simple log noting which probiotic product you’re using, the dose, and any digestive changes you notice.
  • Create a 30-day tracking period starting from the first antibiotic dose. Log daily stool frequency and consistency, any abdominal discomfort, and energy levels. After finishing antibiotics, continue monitoring for 2 weeks since C. difficile diarrhea can develop shortly after antibiotic use ends. Share this log with your healthcare provider at follow-up visits to help them assess whether probiotics were helpful for you personally.

This research summary is for educational purposes only and should not replace professional medical advice. Probiotics are not appropriate for everyone, particularly people with severely weakened immune systems, critical illness, or certain medical conditions. Always consult with your healthcare provider before starting probiotics, especially if you’re taking antibiotics or have underlying health conditions. While this review suggests probiotics are generally safe, individual responses vary. If you develop severe diarrhea, fever, or blood in stool while taking antibiotics, seek immediate medical attention rather than relying on probiotics alone. This summary reflects evidence current as of March 2025 and may be updated as new research emerges.