Probiotics Dosage: How Many Billion CFU You Need
Most probiotic products hold 1 to 10 billion CFU a dose, and a higher count is not necessarily better (NIH). CFU counts live cells. The dose that works depends on the strain, so match the strain on the label to a trial and take that dose.
Based on published research, not medical advice. A weak immune system, a serious illness or pregnancy? Ask your doctor first.
Ready to buy:
Florastor$1.93 a day for 2 capsules (500 mg) of S. boulardii CNCM I-745, a yeast dosed in mg, not CFU. It cut diarrhea from antibiotics in adults across 15 trials (Szajewska 2015), with no clear gain from higher doses (NIH). Why it is our pick.
Costs are brand prices, checked October 19, 2026.
Which probiotic dose is right for you?
Giving it to a child on antibiotics?
In children’s trials, 5 billion CFU a day or more worked better than lower doses (Guo 2019). Culturelle Digestive Daily has 10 billion CFU of LGG, and the brand counts it at the expiry date, so the dose holds to the end of the bottle. Ask your child’s doctor first.
Culturelle Digestive Daily
$0.60 a day · 10 billion CFU
For vaginal health?
The dose study for GR-1 and RC-14 found that more than 100 million live cells a day were needed (Reid 2001); later trials used billions. Jarrow Fem-Dophilus has 5 billion, counted to the best-by date. Keep it in the fridge.
Jarrow Fem-Dophilus
$0.93 a day · 5 billion CFU
For IBS? Check the date on the box.
In the IBS trial, 100 million CFU a day of B. infantis 35624 helped, while 1 million did nothing (Whorwell 2006). Align has 1 billion when made but promises only 10 million by the best-by date, so buy a fresh box.
Align
$1.08 a day · 1 billion CFU when made
Is 50 billion CFU better than 10?
Not by itself. In the IBS trial, 10 billion CFU a day did no better than a placebo, while 100 million helped (Whorwell 2006).
Check when the CFU is counted
Some labels count the CFU when made, others to the best-by date. Live cells die, so prefer the best-by count.
Doses the trials used, by strain
- S. boulardii CNCM I-745 (Florastor): 250 or 1,000 mg a day for travel (Kollaritsch 1993).
- LGG (Culturelle): 1 billion CFU a day lowered infections in children in hospital (Hojsak 2010).
- Mixed probiotics for children on antibiotics: 5 billion CFU a day or more (Guo 2019).
- B. coagulans GBI-30 (Schiff Digestive Advantage): once a day for 8 weeks, in one small IBS trial of 44 people (Hun 2009).
How to take it
- Take it with a meal, or up to 30 minutes before one. In a lab model of the stomach, probiotic bacteria survived best that way (Tompkins 2011).
- With antibiotics, start within 2 days of the first antibiotic dose; that worked better than starting later (NIH).
- Take it every day, as the trials did.
Questions people ask
How many CFU should a probiotic have?
As many as the trial for that strain used. Most products hold 1 to 10 billion CFU a dose; 50 billion of untested strains is not better than 5 billion of a tested one.
Can you take too many probiotics?
Trials found side effects no more often than on a placebo, but many reported harms poorly (Hempel 2011). If you are very ill or your immune system is weak, ask your doctor first.
Related guides
- Best probiotic: every product we compared, ranked by goal
- Probiotics guide: what the research covers
Sources
- Guo Q, et al. “Probiotics for the prevention of pediatric antibiotic-associated diarrhea.” Cochrane Database Syst Rev. 2019. PubMed 31039287
- Whorwell PJ, et al. “Efficacy of an encapsulated probiotic Bifidobacterium infantis 35624 in women with irritable bowel syndrome.” Am J Gastroenterol. 2006. PubMed 16863564
- Reid G, et al. “Probiotic Lactobacillus dose required to restore and maintain a normal vaginal flora.” FEMS Immunol Med Microbiol. 2001. PubMed 11750220
- Kollaritsch H, et al. “Prevention of traveler’s diarrhea with Saccharomyces boulardii. Results of a placebo controlled double-blind study” (in German). Fortschr Med. 1993. PubMed 8486328
- Hojsak I, et al. “Lactobacillus GG in the prevention of nosocomial gastrointestinal and respiratory tract infections.” Pediatrics. 2010. PubMed 20403940
- Tompkins TA, et al. “The impact of meals on a probiotic during transit through a model of the human upper gastrointestinal tract.” Benef Microbes. 2011. PubMed 22146689
- Hun L. “Bacillus coagulans significantly improved abdominal pain and bloating in patients with IBS.” Postgrad Med. 2009. PubMed 19332970
- Hempel S, et al. “Safety of probiotics used to reduce risk and prevent or treat disease.” Evid Rep Technol Assess. 2011. PubMed 23126627
- NIH Office of Dietary Supplements. “Probiotics: Fact Sheet for Health Professionals.” ods.od.nih.gov
- Szajewska H, Kołodziej M. “Systematic review with meta-analysis: Saccharomyces boulardii in the prevention of antibiotic-associated diarrhoea.” Aliment Pharmacol Ther. 2015. PubMed 26216624
- CFU, count basis and serving from each brand’s own label, read October 19, 2026.