Probiotics

Are probiotics safe, and who should avoid them?

Updated 4 Nov 2026

Short answer

For most healthy people, probiotics are unlikely to cause harm, and side effects such as gas are usually minor.[1] Rare blood infections from the microbes have been reported, mostly in people who were severely ill or had a weak immune system.[1] Pregnant women and parents of premature babies should also ask a doctor first.[2][3]

What large reviews show

  • Adults and children on antibiotics. In 37 studies with 11,911 people, side effects affected 10.9% of the probiotic groups and 12.2% of the control groups (moderate certainty). The most common were cramps, nausea, fever, soft stools, gas and a changed sense of taste.[4]
  • Children on antibiotics. Side effects affected 4% of children on probiotics and 6% of the others (low certainty). None of the 24 trials that reported side effects found a serious one caused by probiotics.[5]
  • Irritable bowel syndrome. In 55 trials with more than 7000 people, side effects were not significantly more common with probiotics.[6]

Why the safety data have gaps

Trials report safety in different ways, and some are not designed to answer safety questions.[1][7] A 2011 US government report found no sign of higher risk in trials. It also said that the research was "not well equipped to answer questions on the safety of probiotics in intervention studies with confidence".[7] Possible harms include infections and the transfer of antibiotic resistance genes to other gut microbes.[8]

Blood infections in very ill people

Blood infections are rare, and they are linked to specific microbes:

  • Bacteria. At a Boston hospital, 522 patients in intensive care got Lactobacillus rhamnosus GG, and 6 of them had this strain in the blood. Among 21,652 patients who did not get it, there were 2 such cases.[1] The genomes of the blood samples matched the bacteria in the product.[9]
  • Yeasts. At least 60 reports since 1966 link probiotics with the yeast Saccharomyces cerevisiae to yeast in the blood. Many of these patients were in intensive care, were fed by tube or vein, had a central venous catheter or took strong antimicrobial drugs.[1] Of 108 cases in a later review, 73 were in people treated with Saccharomyces boulardii.[10]

A review of 93 patients concluded that probiotics cannot be considered free of risk for some groups.[11] For people with a weak immune system or a serious disease, the World Gastroenterology Organisation advises only strains and uses with proven effect.[1]

Premature babies

The US FDA warns that premature babies given probiotics can get invasive, possibly fatal infections from the microbes. It reported one death in 2023 and more than two dozen other adverse events since 2018.[3] See Are probiotics safe for babies?

Pregnancy

A 2021 Cochrane review found more pre-eclampsia with probiotics.[2] See Can you take probiotics during pregnancy?

Product quality

In the US, many probiotics are sold as dietary supplements, which do not need FDA approval before they are sold. Some products contained microbes that were not on the label.[8]

Who should ask a doctor first

  • people with a weak immune system or a serious illness[1]
  • people in intensive care, on tube feeding or with a central venous catheter[1]
  • pregnant women[2]
  • parents of premature babies[3]

Sources (11)

  1. Probiotics: Fact Sheet for Health Professionals. NIH Office of Dietary Supplements, 2025. ods.od.nih.gov
  2. Probiotics for preventing gestational diabetes. Davidson SJ, Barrett HL, Price SA, Callaway LK, Dekker Nitert M Cochrane Database Syst Rev, 2021. PMID 33870484
  3. FDA Raises Concerns About Probiotic Products Sold for Use in Hospitalized Preterm Infants. US Food and Drug Administration, 2023. www.fda.gov
  4. Probiotics for the prevention of Clostridioides difficile-associated diarrhea in adults and children. Esmaeilinezhad Z, Ghosh NR, Walsh CM, Steen JP, Burgman AM, Mertz D, et al. Cochrane Database Syst Rev, 2025. PMID 40931979
  5. Probiotics for the prevention of pediatric antibiotic-associated diarrhea. Guo Q, Goldenberg JZ, Humphrey C, El Dib R, Johnston BC Cochrane Database Syst Rev, 2019. PMID 31039287
  6. Efficacy of Probiotics in Irritable Bowel Syndrome: Systematic Review and Meta-analysis. Goodoory VC, Khasawneh M, Black CJ, Quigley EMM, Moayyedi P, Ford AC Gastroenterology, 2023. PMID 37541528
  7. Risk and safety of probiotics. Doron S, Snydman DR Clin Infect Dis, 2015. PMID 25922398
  8. Probiotics: Usefulness and Safety. NIH National Center for Complementary and Integrative Health, 2019. www.nccih.nih.gov
  9. Genomic and epidemiological evidence of bacterial transmission from probiotic capsule to blood in ICU patients. Yelin I, Flett KB, Merakou C, Mehrotra P, Stam J, Snesrud E, et al. Nat Med, 2019. PMID 31700189
  10. Epidemiology of Saccharomyces fungemia: A systematic review. Vinayagamoorthy K, Pentapati KC, Prakash H Med Mycol, 2023. PMID 36806741
  11. Infectious complications following probiotic ingestion: a potentially underestimated problem? A systematic review of reports and case series. Costa RL, Moreira J, Lorenzo A, Lamas CC BMC Complement Altern Med, 2018. PMID 30541524

More about probiotics

What are probiotics?Do probiotics change your gut bacteria?Is a higher CFU count better?Which foods contain probiotics?What are probiotics used for?Do probiotics prevent diarrhea from antibiotics and C. difficile?

For education; not medical advice. Talk to a doctor before you start, stop or change a supplement.