Best Probiotics for Immune Support (2026): What the Research Shows
The best probiotic for immune support is Culturelle Digestive Daily: its strain, LGG, lowered gut and respiratory infections in a trial of 742 children in hospital, at $0.60 a day. Across 23 trials, probiotics may cut the number of people who catch a cold by about a quarter, but the evidence is weak.
By Erin Rose Updated October 19, 2026 How we rank
Brand prices, checked October 19, 2026.
Our pick for: Fewer infections
Culturelle Digestive Daily
First of the 4 we compare: LGG, tested against infections, and on USP Verified
- Strain
- LGGL. rhamnosus GG
- Amount
- 10 billion CFUCounted at the expiry date
- A day
- $0.60One capsule, at the brand’s price
- Box
- 30 capsules$17.99 at the brand
- Storage
- Room temperatureNo fridge needed
- Testing list
- USP VerifiedUSP lists Culturelle Digestive Daily
Why we pick it In 742 children in hospital, LGG lowered gut and respiratory infections against a placebo. Culturelle sells LGG at 10 billion CFU, counted to the expiry date, and it is on a public testing list.
What you give up Most trials on colds used other strains that Culturelle does not have, and the evidence for adults is thin.
Which probiotic is right for you?
For colds, no product we compare holds the strains from most of the cold trials. LGG is the closest match with a trial.
Already on antibiotics for an infection?
Take S. boulardii during the course to lower the chance of diarrhea from the antibiotic. In adults, it cut that risk by about half in trials. Florastor holds S. boulardii (strain CNCM I-745). More on probiotics with antibiotics.
Florastor
$1.93 a day · S. boulardii CNCM I-745, 2 capsules
Want to catch fewer colds?
Hand washing and your yearly vaccines are the basics. A probiotic is an add-on, not a shield.
Probiotics for immune support we compared, ranked
Strains with an infection trial first, then the rest. Costs are a day at each brand’s own price (Schiff from Vitacost’s 60-capsule bottle, as the brand has no store).
| Probiotic | Cost a day | Why it is or is not a pick |
|---|---|---|
| Culturelle Digestive DailyLGG, 1 capsule | $0.60 | Our pick: LGG lowered infections in a hospital trial |
| FlorastorS. boulardii, 2 capsules | $1.93 | For diarrhea from antibiotics, not colds |
| Schiff Digestive AdvantageB. coagulans, 1 capsule | $0.36 | B. coagulans; no infection trials we found |
| Seed DS-0124 strains, 2 capsules | $2.00 | 24 strains; trials are the brand’s own |
What the trials found
A Cochrane review of 23 trials with 6,950 people found that probiotics may cut the number of people who get a cold by about a quarter (risk ratio 0.76) and may shorten a cold by about a day. The reviewers rated that as low-certainty evidence, but they also found, with more confidence, that people on probiotics needed antibiotics for a cold less often (risk ratio 0.58). Most trials gave one or two strains every day for over 3 months (Zhao 2022).
In a hospital trial, 742 children drank LGG or a placebo for their stay. Those on LGG had fewer gut and respiratory infections (Hojsak 2010). That trial gave 1 billion CFU in a fermented milk drink; Culturelle gives 10 billion in a capsule, and it was children in hospital, not healthy adults at home.
If your immune system is weak from illness or medicine, ask your doctor before taking any live probiotic: rare blood infections have been reported in people who were already ill (Hempel 2011).
How we rank
Two things, in order: does the label name a strain tested against infections, and what a day costs at the brand’s own price. We also checked NSF, USP, Informed Choice and Informed Sport; only Culturelle is on one. We don’t score probiotics out of 10; dose depends on the strain. More on our method.
Questions people ask
Do probiotics boost your immune system?
“Boost” is a marketing word. What trials measured was colds and infections. A Cochrane review found probiotics may mean fewer people catch a cold and colds that end about a day sooner, but it rated the evidence as low.
Which probiotic strain has been studied in respiratory research?
Many. The cold trials in the Cochrane review mostly used L. plantarum HEAL9 or L. paracasei strains (8700:2, N1115). LGG, the strain in Culturelle, lowered respiratory infections in children in hospital.
How long did the trials run?
Most cold trials gave a probiotic every day for more than 3 months. The LGG trial ran for as long as each child stayed in hospital.
Sources
- Zhao Y, et al. “Probiotics for preventing acute upper respiratory tract infections.” Cochrane Database Syst Rev. 2022. PubMed 36001877
- Hojsak I, et al. “Lactobacillus GG in the prevention of nosocomial gastrointestinal and respiratory tract infections.” Pediatrics. 2010. PubMed 20403940
- Szajewska H, Kołodziej M. “Systematic review with meta-analysis: Saccharomyces boulardii in the prevention of antibiotic-associated diarrhoea.” Aliment Pharmacol Ther. 2015. PubMed 26216624
- Hempel S, et al. “Safety of probiotics used to reduce risk and prevent or treat disease.” Evid Rep Technol Assess. 2011. PubMed 23126627
- USP Verified products list (Culturelle Digestive Daily Probiotic capsules). Labels and prices from each brand, read October 19, 2026; Schiff at Vitacost.