Probiotics

What are probiotics used for?

Updated 4 Nov 2026

Short answer

Mostly for the gut. The results depend on the strain and on the health problem, so a result from a review of many probiotics does not apply to every product.[1][2] What reviews found:

  • Diarrhea from antibiotics. A 2025 Cochrane review found it in 23% of people who took probiotics and 27.4% of the others (low certainty).[3]
  • Irritable bowel syndrome (IBS). In 82 trials, some strains and mixes may help, but the certainty was low to very low for almost all results.[4]
  • Constipation. In 30 trials in adults, 57% improved with probiotics and 44% without. Stool frequency rose with Bifidobacterium lactis, but not with several other products.[5]
  • Colds. A review of 23 trials found that fewer people had upper airway infections (low certainty).[6] See immune support.
  • Mood. Reviews found less depression and anxiety, but the trials differ widely and their quality is limited.[7][8]
  • Sleep. A review of 15 trials found better scores for sleep quality, with some risk of bias.[9]
  • Weight. Results are inconsistent, and the average effects are small.[1]
  • Iron. In a pooled analysis of 8 studies, Lactobacillus plantarum 299v raised iron absorption. Other strains did not improve iron status.[10] See essential health.
  • Skin. A Cochrane review found little or no difference in symptoms of eczema.[11]
  • Gums. In 14 studies of periodontitis, a gum disease, adding probiotics to usual treatment lowered plaque and bleeding.[12]
  • Fatigue. Of 13 trials with 513 athletes and active people, 10 reported improvements in measures such as endurance or gut symptoms. The authors concluded that at least 15 billion colony-forming units (CFU, live cells) a day for at least 28 days may reduce fatigue.[13]
  • Allergic rhinitis (hay fever). A review of 28 studies found less severe symptoms, but the results varied widely.[14]

Sources (14)

  1. Probiotics: Fact Sheet for Health Professionals. NIH Office of Dietary Supplements, 2025. ods.od.nih.gov
  2. Strain-Specificity and Disease-Specificity of Probiotic Efficacy: A Systematic Review and Meta-Analysis. McFarland LV, Evans CT, Goldstein EJC Front Med (Lausanne), 2018. PMID 29868585
  3. 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
  4. 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
  5. Probiotics and synbiotics in chronic constipation in adults: A systematic review and meta-analysis of randomized controlled trials. van der Schoot A, Helander C, Whelan K, Dimidi E Clin Nutr, 2022. PMID 36372047
  6. Probiotics for preventing acute upper respiratory tract infections. Zhao Y, Dong BR, Hao Q Cochrane Database Syst Rev, 2022. PMID 36001877
  7. Effects of Prebiotics and Probiotics on Symptoms of Depression and Anxiety in Clinically Diagnosed Samples: Systematic Review and Meta-analysis of Randomized Controlled Trials. Asad A, Kirk M, Zhu S, Dong X, Gao M Nutr Rev, 2025. PMID 39731509
  8. The efficacy of probiotics, prebiotics, and synbiotics on anxiety, depression, and sleep: a systematic review and meta-analysis of randomized controlled trials. Zhang J, Zhu L, Meng Q, Wang Z, Zhu H BMC Psychiatry, 2025. PMID 41310510
  9. Effects of probiotics on sleep parameters: A systematic review and meta-analysis. Ito H, Tomura Y, Kitagawa Y, Nakashima T, Kobanawa S, Uki K, et al. Clin Nutr ESPEN, 2024. PMID 39094854
  10. A Systematic Review and Meta-Analysis on the Effects of Probiotic Species on Iron Absorption and Iron Status. Vonderheid SC, Tussing-Humphreys L, Park C, Pauls H, OjiNjideka Hemphill N, LaBomascus B, et al. Nutrients, 2019. PMID 31816981
  11. Probiotics for treating eczema. Makrgeorgou A, Leonardi-Bee J, Bath-Hextall FJ, Murrell DF, Tang ML, Roberts A, et al. Cochrane Database Syst Rev, 2018. PMID 30480774
  12. Clinical effects of probiotics on the treatment of gingivitis and periodontitis: a systematic review and meta-analysis. Benavides-Reyes C, Cabello I, Magán-Fernández A, Rodríguez-Barranco M, Usta SN, Mesa F BMC Oral Health, 2025. PMID 40186219
  13. "Do probiotics mitigate GI-induced inflammation and perceived fatigue in athletes? A systematic review". Kearns RP, Dooley JSG, Matthews M, McNeilly AM J Int Soc Sports Nutr, 2024. PMID 39193818
  14. The Efficacy and Safety of Probiotics for Allergic Rhinitis: A Systematic Review and Meta-Analysis. Luo C, Peng S, Li M, Ao X, Liu Z Front Immunol, 2022. PMID 35663980

More about probiotics

What are probiotics?Do probiotics change your gut bacteria?Is a higher CFU count better?Which foods contain probiotics?Do probiotics prevent diarrhea from antibiotics and C. difficile?Are probiotics safe, and who should avoid them?

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