probiotics

Probiotics are live microorganisms — most commonly bacteria from the Lactobacillus and Bifidobacterium genera, and sometimes yeasts such as Saccharomyces boulardii — that are intended to provide a health benefit when consumed or applied to the body. They are sold as dietary supplements (capsules, powders, liquids) and are also found in yogurt and other fermented foods. Effects appear to be specific to the particular strain and dose, so results from one product do not necessarily apply to another.

Evidence varies a great deal by condition and by the specific strain studied, and for most uses it is limited or inconclusive. NCCIH notes that giving probiotics alongside antibiotics was associated with about half the likelihood of antibiotic-associated diarrhea in non-hospitalized people, though it calls these conclusions "tentative because the quality of the studies was only moderate" (and no benefit has been demonstrated in elderly people). Researchers are described as "moderately certain" that probiotics can reduce the risk of C. difficile diarrhea in people taking antibiotics, though the most useful types, dose, and duration remain uncertain. For IBS, probiotics "may have beneficial effects on global IBS symptoms and abdominal pain," but "it was not possible to draw definite conclusions about their effectiveness." A benefit was suggested for inducing or maintaining remission in ulcerative colitis, but not for Crohn's disease. For many other uses — including atopic dermatitis, asthma, acne, and upper respiratory and urinary tract infections — NCCIH found evidence that was low-quality, inconsistent, or showed no clear benefit. Probiotic dietary supplements are not reviewed by the FDA for effectiveness before marketing and are not permitted to make claims about preventing or treating disease without FDA consent.

There is no established standard dose. Amounts are listed in colony-forming units (CFU), and NCCIH notes we do not know how much of a probiotic a person would need to take; the effective dose and strain appear to differ from product to product and from one condition to another, so a benefit shown for one probiotic does not transfer to others. Because formulations are not interchangeable and product quality varies, talk with your health care provider before starting a probiotic — especially about which strain and amount, if any, might fit your situation.

Probiotics have an extensive history of apparently safe use, particularly in generally healthy people, but few studies have examined their safety in detail. NCCIH advises that the risk of harmful effects is greater in people with severe illnesses or compromised immune systems, in whom the potential risks should be carefully weighed against the benefits. In 2023 the FDA warned health care providers that premature infants given probiotics are at risk of severe, potentially fatal infections caused by the microorganisms in the products; cases of severe or fatal infection have been reported in this group.

In generally healthy people, probiotics usually cause few side effects, which may include mild digestive symptoms such as gas. More serious theoretical harms include infections, the production of harmful substances by the probiotic microorganisms, and transfer of antibiotic-resistance genes from probiotic microorganisms to other microbes in the digestive tract; serious infections have been reported in premature infants and in people who are severely ill or have compromised immune systems. Some probiotic products have also been reported to contain microorganisms other than those listed on the label, which in some cases may pose health risks.

Authoritative NCCIH guidance does not detail specific drug interactions for probiotics. They are most often studied alongside antibiotics, where they have been used to lower the risk of antibiotic-associated diarrhea. Because live microorganisms may carry added risk in people who are immunocompromised or taking immunosuppressive medications, and because supplement quality varies, tell your health care provider about any probiotic you use and review it together with your other medications.