Probiotic benefits

Do probiotics work for preventing antibiotic-associated diarrhea?

In children. The 2019 Cochrane review pooled 33 trials (6,352 participants) in children aged 0–18 taking antibiotics. The diarrhea rate was 8% (259/3,232) in the probiotic group and 19% (598/3,120) in the control group (RR 0.45; 95% CI 0.36–0.56; NNTB 9; moderate certainty). The result remained significant even when the most unfavorable plausible assumption was applied to missing data (RR 0.61). In the subgroup analysis of doses of 5 billion CFU/day and above (interaction P = 0.01), 8% versus 23% was seen in the high-dose trials; the review states that this subgroup finding needs to be confirmed by a large, well-designed multicenter trial. Serious adverse effects were not attributed to probiotics; however, in observational reports outside the trials, serious events have been reported in children with central venous catheters or suppressed immunity. ^[1]

In adults. The 2021 BMJ Open meta-analysis pooled 42 trials (11,305 participants) in adults taking antibiotics: the risk was 37% lower with probiotics (RR 0.63; 95% CI 0.54–0.73; moderate certainty by GRADE). A high dose of the same strain was more effective than a low dose (RR 0.54); only certain species, mostly of the Lactobacillus and Bifidobacterium genera, were found effective. No difference was seen in trials with a low baseline diarrhea risk; the authors state that the findings may not be applicable to low-risk clinical scenarios. ^[2]

The common message of these two reviews is that the effect does not apply to all probiotics: the result depends on the strain and products studied and on the person’s diarrhea risk.

Do probiotics prevent C. difficile infection?

The 2025 Cochrane update includes 47 trials (15,260 participants) in children and adults taking antibiotics. For C. difficile-associated diarrhea, in 38 trials (13,179 participants) the event rate was 1.6% (110/6,787) in the probiotic group and 3.2% (203/6,392) in the control group (RR 0.50; 95% CI 0.38–0.64; low certainty); the absolute reduction is 1.6%, and one case can be prevented for every 65 people (NNT 65; 95% CI 48–97). In 27 trials, C. difficile data were missing (2–45%); the result was found robust to assumptions about missing data. For detection of C. difficile in stool (asymptomatic carriage), the difference was not significant (RR 0.87; 95% CI 0.68–1.11). In 28 trials, the authors had ties to a probiotic company or company support. The authors say that short-term use is unlikely to be associated with adverse effects in people with non-suppressed immunity taking systemic antibiotics; large trials comparing people at low baseline risk with placebo are needed. ^[3]

Do probiotics shorten acute diarrhea in children?

Cochrane’s 2020 update includes 82 trials (12,127 participants; 11,526 children, 412 adults). In many trials the risk of bias was high or unclear; results were highly variable and publication bias was detected. In trials at low risk across all bias indicators, there was no difference in diarrhea lasting 48 hours or longer (RR 1.00; 95% CI 0.91–1.09; 2 trials, 1,770 participants; moderate certainty). A 8.64-hour reduction in diarrhea duration was estimated; however, the confidence interval ranged from a 29.4-hour reduction to a 12.1-hour increase (6 trials, 3,058 participants; very low certainty). In subgroups limited to L. rhamnosus GG and S. boulardii, effect sizes were also similar to the main analysis and variability persisted; in six L. reuteri trials (433 participants) the findings were consistent, but all had a risk of bias. Hospital stay was shortened by an average of 18 hours, but between-trial variability was very high (I² = 96%). No serious adverse effect was attributed to probiotics. ^[4]

The authors’ conclusion is that probiotics probably make little or no difference to the number of cases of diarrhea lasting 48 hours or longer, and that it is uncertain whether they shorten the duration of diarrhea. According to the authors, this analysis rests on large trials at low risk of bias. ^[4]

Are probiotics good for irritable bowel syndrome?

Two sources should be read side by side. The recommendation summary of the ACG’s 2021 IBS guideline includes the statement “We recommend against the use of probiotics for global IBS symptoms”; the recommendation is conditional and the evidence is of very low certainty. ^[5] In contrast, a meta-analysis based on a search up to December 2013 pooled 43 RCTs: the risk of IBS symptoms persisting was lower with probiotics than with placebo (RR 0.79; 95% CI 0.70–0.89); benefit was seen in global symptoms, abdominal pain, and bloating and flatulence scores. The authors state that which species and strains are most beneficial remains unclear. ^[6]

The meta-analysis reflects trials published up to December 2013, whereas the guideline reflects an assessment made in 2021 using the GRADE method; the two answer the same question at different dates and with different certainty criteria. Because which strain is effective remains unclear, summarizing these two results in a single sentence (“it works” or “it does not work”) would make the evidence look more definitive than it is.

Are probiotics good for infant colic?

The evidence in this area belongs to a single strain, L. reuteri DSM 17938. A meta-analysis using individual participant data from four double-blind RCTs evaluated 345 infants with colic (174 probiotic, 171 placebo). In the probiotic group, crying and/or fussing time decreased on average 25.4 minutes more from baseline at day 21 (95% CI −47.3 to −3.5); the likelihood of treatment success was about double (adjusted incidence rate ratio 1.7; 95% CI 1.4–2.2). The effect was marked in breastfed infants (NNT 2.6 for success on day 21; 95% CI 2.0–3.6) and nonsignificant in formula-fed infants; there were insufficient data for formula-fed infants. Some of the authors declared receiving fees outside this work from probiotic and formula companies, including the company that markets the strain studied. ^[7] This result cannot be generalized to other strains or to “probiotic drops.”

Do probiotics reduce the risk of necrotizing enterocolitis in preterm infants?

Cochrane (2023) pooled 60 trials (11,156 infants); these were infants born before 32 weeks or with birth weight below 1,500 g. Most trials were small (median 145 infants) and product formulations differed. The risk of necrotizing enterocolitis (NEC) was lower with probiotics (RR 0.54; 95% CI 0.46–0.65; 57 trials, 10,918 infants; low certainty; NNTB 33). The risk of death also decreased slightly (RR 0.77; moderate certainty; NNTB 50). For late-onset invasive infection, the effect is stated to be most likely little or none (RR 0.89; 95% CI 0.82–0.97; moderate certainty). In extremely preterm or extremely low birth weight infants, the effect on NEC may be little or none (RR 0.92; 95% CI 0.69–1.22; 10 trials; low certainty). The authors state that larger, high-quality trials are needed. ^[8]

The trials were conducted in very preterm or very low birth weight infants; the results are valid for this population.

The 2021 clinical report of the American Academy of Pediatrics (AAP), on the other hand, reaches a different conclusion: it accepts that multi-strain products reduced NEC and death in meta-analyses and that the effect of single-strain products is more uncertain; but because there is no pharmaceutical-grade product made in the USA, some supplement products have been recalled for contamination, safety and efficacy data are conflicting and these infants are very fragile, it states that the current evidence does not support routine, universal probiotic administration to preterm infants, especially those with birth weight below 1,000 g. ^[14] In October 2023, the US Food and Drug Administration (FDA) announced that products containing live bacteria or yeast carry a risk of invasive and potentially fatal infection in hospitalized preterm infants; it stated that some products used to prevent NEC contributed to invasive disease, including an infant death in 2023, and that there is no probiotic product approved as a drug for infants in the USA. ^[15] In these infants, the decision belongs to the neonatal team.

Do probiotics prevent eczema?

The World Allergy Organization (WAO) concluded in its 2015 allergy prevention guideline that the available evidence does not show that probiotic supplementation reduces the risk of developing allergy in children; however, when all critical outcomes are considered together, a net benefit, resulting mainly from prevention of eczema, is likely. The panel recommended probiotic use in pregnant women at high risk of having an allergic child, in breastfeeding mothers of infants at high risk of allergy, and in infants at high risk of allergy; all recommendations are conditional and based on very low certainty evidence. ^[9] The guideline dates from 2015; the evidence search was carried out up to November 2014.

Do probiotics work against colds and upper respiratory tract infections?

Cochrane (2022) included 23 trials (6,950 participants; children, adults, older adults) in the meta-analysis. At least one upper respiratory tract infection: RR 0.76 (95% CI 0.67–0.87; 16 trials; low certainty). Three or more infections: RR 0.59 (95% CI 0.38–0.91; 4 trials, 763 participants; moderate certainty). The mean duration of an episode was 1.22 days shorter (95% CI −2.12 to −0.33; low certainty). The proportion of participants using prescribed antibiotics was also lower (RR 0.58; 95% CI 0.42–0.81; moderate certainty). There was no difference in the risk of adverse effects (RR 1.02), and adverse effects were mostly mild digestive complaints. Trials in which more than 50% had received influenza vaccination were excluded. ^[10] The inference is not “immunity is strengthened” but a small-to-moderate, low-certainty reduction in the number of infections.

Do probiotics help in Helicobacter pylori treatment?

In a 2025 meta-analysis pooling 19 RCTs (2,973 samples) in patients with H. pylori infection receiving bismuth quadruple therapy, adding a probiotic increased the eradication rate (OR 1.49; 95% CI 1.20–1.85; I² = 0%). The authors report finding benefit particularly with S. boulardii and multi-strain mixtures, and a reduction in treatment-related adverse effects. ^[11] In the trials, the probiotic was compared as an addition to bismuth quadruple therapy; it was not examined as a treatment on its own.

Do probiotics help with weight loss?

In an umbrella review pooling five systematic reviews and 18 meta-analyses, probiotics reduced mean body weight by 0.59 kg (95% CI −0.74 to −0.44), body mass index by 0.30 kg/m² (95% CI −0.36 to −0.25) and fat mass by 0.86 kg. The authors state that the reliability of the evidence is limited because of trials with weak designs and small samples. ^[12] The review’s conclusion takes the form of “potential benefit,” and the authors state that larger trials are needed.

Do probiotics affect mood and depression?

In a meta-analysis pooling 19 double-blind, placebo-controlled trials (1,901 participants), probiotics overall produced greater improvement in depressive symptoms than placebo. The benefit was significant in patients diagnosed with major depression; it was not significant in other clinical conditions and in the general population. Multi-strain products were found more effective; the authors state that strain- and combination-specific effects need to be confirmed with larger trials. ^[13]

This guide does not recommend personal products or doses; the results in the table are averages for specific strains and groups.