Probiotics are live microorganisms, mainly bacteria and some yeasts, that give a health benefit when taken in adequate amounts. Their effects depend on the specific strain, so results for one product do not carry over to another.
Also known as: probiotic, Lactobacillus, Bifidobacterium, Saccharomyces boulardii, LGG.
Probiotics are counted in colony-forming units (CFU). ODS says many products contain 1 to 10 billion CFU per dose and some 50 billion or more, but higher counts are not necessarily more effective. In antibiotic-diarrhea trials of Lactobacillus rhamnosus GG, amounts ranged from 400 million to 120 billion CFU for 10 days to 3 months (ODS). These are study protocols, not a recommendation.
It is sold in the US as a dietary supplement. Under the 1994 dietary supplement law (DSHEA), FDA does not approve dietary supplements before they are marketed, and the maker, not FDA, is responsible for safety and labeling. ODS advises looking for labels that state CFU at the end of shelf life, not at manufacture, because probiotics can die during storage.
What studies show: a 2019 Cochrane review of 33 trials in 6,352 children taking antibiotics found diarrhea in 8% of those given probiotics versus 19% of controls (moderate-certainty evidence) (Guo 2019). Per ODS, Lactobacillus rhamnosus GG cut antibiotic-associated diarrhea from 22.4% to 12.3% (significant only in children) and Saccharomyces boulardii from 17.4% to 8.2% in adults, starting within 2 days of the first antibiotic dose worked better, and no benefit was seen in adults 65 and older. For IBS, ODS says probiotics have a modest benefit in low-quality studies, and effects on body weight were small and of questionable clinical value.
Safety, per ODS: probiotics are unlikely to harm healthy people, and side effects are usually minor, such as gas. They have been linked to blood infections (bacteria or fungi in the blood), mostly in people who were severely ill or had weak immune systems. In 2023 FDA warned that giving probiotics to preterm infants may cause invasive, potentially fatal disease, citing one infant death and more than two dozen other adverse events.
Probiotics are live microorganisms that act in the gut and are not absorbed like a drug, so a half-life or time to peak does not apply. ODS says they may colonize the gut only temporarily, in patterns that differ from person to person.
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