Probiotics

Is a higher CFU count better?

Updated 4 Nov 2026

Short answer

Not always. The NIH fact sheet says that products with more colony-forming units (CFU, live cells) are not necessarily more effective.[1] Results differ by strain:

  • Higher dose helped. In children on antibiotics, at least 5 billion CFU a day lowered diarrhea more than lower doses.[2] In 503 adult hospital patients, a four-strain mix at 17 billion CFU gave 12.5% diarrhea, 4.17 billion CFU gave 19.6% and placebo 24.6%.[3]
  • No clear dose effect. Studies of Saccharomyces boulardii showed no clear link between dose and effect.[1]
  • Low dose worked. In 654 children on antibiotics, Limosilactobacillus reuteri DSM 17938 at 0.2 billion CFU lowered diarrhea at 14 days from 16.7% to 7.9%.[4]
  • High dose did not work. In about 3000 hospital patients aged 65 and older, a mix of 60 billion organisms a day did not lower diarrhea (10.8% against 10.4%).[5]

Sources (5)

  1. Probiotics: Fact Sheet for Health Professionals. NIH Office of Dietary Supplements, 2025. ods.od.nih.gov
  2. Probiotics for the prevention of pediatric antibiotic-associated diarrhea. Guo Q, Goldenberg JZ, Humphrey C, El Dib R, Johnston BC Cochrane Database Syst Rev, 2019. PMID 31039287
  3. Probiotics reduce symptoms of antibiotic use in a hospital setting: a randomized dose response study. Ouwehand AC, DongLian C, Weijian X, Stewart M, Ni J, Stewart T, et al. Vaccine, 2014. PMID 24291194
  4. Effect of Limosilactobacillus reuteri DSM17938 to prevent antibiotic-associated diarrhea in children: prospective, multi-center, randomized, placebo-controlled clinical trial (PEARL Study). Dinleyici EC, Ozen M, Guven S, Dalgic N, Karbuz A, Sutcu M, et al. Eur J Pediatr, 2025. PMID 40488914
  5. Lactobacilli and bifidobacteria in the prevention of antibiotic-associated diarrhoea and Clostridium difficile diarrhoea in older inpatients (PLACIDE): a randomised, double-blind, placebo-controlled, multicentre trial. Allen SJ, Wareham K, Wang D, Bradley C, Hutchings H, Harris W, et al. Lancet, 2013. PMID 23932219

More about probiotics

What are probiotics?Do probiotics change your gut bacteria?Which foods contain probiotics?What are probiotics used for?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.