Do Probiotics Work? An Honest Overview of the Evidence by Strain and Condition
Whether probiotics work depends on the strain, the condition and the person. A table of what reviews found, how strong the evidence is, and where proper evidence was not found.
Content last updated . This page has not been medically reviewed.
Evidence labels used here: promising but limited (some trials or reviews suggest a benefit, with low or moderate certainty), mixed (reviews disagree), insufficient evidence, no good evidence of benefit, and Proper evidence not found (we looked and found nothing usable). Most review numbers below come from NCCIH's summaries of reviews published between 2014 and 2018, plus one 2025 Cochrane update. Newer research may exist that we did not read. Those reviews usually pooled many different probiotics together, so a result for "probiotics" is not a result for any one product.
What the sources found, by condition
| Question | What the source found | Label |
|---|---|---|
| Preventing diarrhea in people taking antibiotics | A 2025 Cochrane review of 40 trials (13,419 adults and children given antibiotics) found diarrhea in 23% of the probiotic groups and 27.4% of the comparison groups (risk ratio 0.67), with low-certainty evidence [3]. An older review found no benefit demonstrated in people 65 and over, partly because few studies included them [1]. | Promising but limited |
| Preventing C. difficile diarrhea in people taking antibiotics | The same Cochrane review (38 trials, 13,179 people) found C. difficile-associated diarrhea in 1.6% of the probiotic groups versus 3.2% of the comparison groups (risk ratio 0.50), low certainty [3]. | Promising but limited |
| Irritable bowel syndrome | A 2018 review of 53 studies (5,545 people) found probiotics may help overall symptoms and abdominal pain, but could not say which species or strains are most likely to help [1]. A technical review for the American Gastroenterological Association (AGA) said no single strain or combination had been studied rigorously enough [4]. | Promising but limited; strain unknown |
| Ulcerative colitis | A 2014 review of 21 studies (1,700 people) suggested probiotics, prebiotics or synbiotics added to usual treatment could help induce or maintain remission [1]. | Mixed |
| Crohn's disease | The same 2014 review (14 studies, 746 people) did not find evidence of benefit [1]. | No good evidence of benefit |
| Infant colic | A 2018 review of 7 studies (471 infants), 5 using Lactobacillus reuteri DSM 17938, linked that strain to success, mainly in exclusively breastfed babies [1]. | Promising but limited; strain-specific |
| Constipation | A 2014 review in adults found some evidence of benefit, especially for Bifidobacterium lactis. Two 2017 reviews in children disagreed with each other [1]. | Mixed |
| Eczema (atopic dermatitis) treatment in children | A 2017 review of 13 studies (1,271 people) found no consistent benefit [1]. The NHS says there is no evidence probiotics can help treat eczema [2]. | No good evidence of benefit |
| Colds and other upper respiratory infections | A 2015 evaluation of 12 studies (3,720 people) suggested fewer and shorter infections, but the evidence was rated low quality [1]. | Insufficient evidence |
| Preventing urinary tract infections | A 2015 review of 9 studies (735 people) did not find evidence of benefit [1]. | No good evidence of benefit |
| Acne | The 2016 American Academy of Dermatology guideline, as described by NCCIH, found the evidence not strong enough for any recommendation [1]. | Insufficient evidence |
| Daily use by healthy people for general "gut health" or "immunity" | We searched NCCIH, the NHS, the AGA review and PubMed summaries for an overall benefit in healthy people and found none stated. | Proper evidence not found |
Benefit in one row says nothing about any other row. Biomarker changes (for example a lab marker or stool bacteria count) are not the same as feeling better or avoiding illness, and the rows above are about symptoms and illness outcomes.
Why results differ so much
- Strain. NCCIH notes that if one kind of Lactobacillus helps prevent an illness, that does not mean another kind, or any Bifidobacterium, would [1]. The AGA review states that the effect of probiotics is species- and strain-specific [4]. See why one strain's result does not transfer.
- Trial quality. In the 2025 Cochrane update, about 30% of studies lacked a published protocol or registration, and 28 studies had an author affiliated with, or funding from, a probiotic company [3].
- Dose. A review of dose-response studies saw a positive link between dose and antibiotic-associated diarrhea risk, but no dose-response for several other outcomes, and it said that did not prove one does not exist [5]. These are study findings, not advice.
- Product versus trial. The NHS says there is likely a huge difference between the pharmaceutical-grade probiotics that show promise in trials and the yogurts and supplements sold in shops [2]. More on why trials disagree.
Where to go next
For specific conditions, see antibiotic-associated diarrhea trials, IBS guidelines and trials and infant colic. To judge a product, see quality testing and certifications.Frequently asked questions
Do probiotics work for everyone?
No. Reviews pooled many strains and people, and NCCIH says that for most uses it is still unknown which probiotics help and who benefits most [1].
Is there proof that probiotics help healthy people?
We did not find proof in the sources we read. The NHS says there is little evidence for many of the health claims made about probiotics [2]. Proper evidence not found for routine daily use in healthy adults.
Can I assume a result for one probiotic applies to another?
No. NCCIH and the NHS both say different probiotics may have different effects, and benefit for one problem does not show a probiotic helps another [1][2].
Do probiotics prevent diarrhea from antibiotics?
A 2025 Cochrane review found fewer cases of antibiotic-associated diarrhea in probiotic groups (23% versus 27.4%), but the certainty was low [3].
Are probiotics always safe?
Not always. Risk is greater with severe illness or weakened immunity, and the FDA warns about serious infections in preterm infants [1][6].
More details: evidence, limits and cautions
The details behind this page: cautions, limits of the evidence and where sources disagree. Open any note to read it.
Safety and who should ask first
References
- Probiotics: Usefulness and Safety, NCCIH, National Institutes of Health (page undated; reviews it summarizes date from 2014 to 2018). Read 2026-10-22.
- Probiotics, NHS (UK), last reviewed 24 November 2022. Read 2026-10-22.
- Esmaeilinezhad Z et al. Probiotics for the prevention of Clostridioides difficile-associated diarrhea in adults and children. Cochrane Database Syst Rev 2025;9:CD006095. Read 2026-10-22.
- Preidis GA et al. AGA Technical Review on the Role of Probiotics in the Management of Gastrointestinal Disorders. Gastroenterology 2020;159(2):708-738. Read 2026-10-22.
- Ouwehand AC. A review of dose-responses of probiotics in human studies. Benef Microbes 2017;8(2):143-151. Read 2026-10-22.
- Risk of Invasive Disease in Preterm Infants Given Probiotics Formulated to Contain Live Bacteria or Yeast, US Food and Drug Administration, 29 September 2023. Read 2026-10-22.