Cured at 30 days: 88% vs 40%
Anukam 2006, Microbes and Infection · Source
Lactobacillus rhamnosus
Strain UALr-18 (UAS Labs)
One of the most-studied probiotic species, found in the gut and in many women's vaginal flora, with trials on vaginal health, pregnancy and the gut.
Most-studiedone of the best-researched probiotic species
72postmenopausal women in a vaginal flora trial of a related strain
10strains in the Daily Probiotic blend
Why we love it
We wanted species that people already carry. L. rhamnosus lives in the gut and is often found in the vaginal microbiome too. It is also one of the species researchers have studied most in women taking probiotics by mouth, so it was a natural part of our blend.
What does the research show?
Bacterial vaginosis (BV)
Researchers gave oral GR-1 with RC-14 alongside standard antibiotics. In a trial of 125 women in Nigeria, 88% were cured at 30 days compared with 40% on antibiotics plus placebo. A later trial of 126 women in China found no added benefit. A 2022 review of 20 trials found a modest overall benefit when probiotics were added to antibiotics, with large differences between trials.
Vaginal yeast
In a trial of 55 women given one dose of fluconazole, those who also took GR-1 with RC-14 for 4 weeks had less yeast on culture (10% vs 39%). A separate trial of 278 women taking antibiotics found that an unnamed L. rhamnosus product, taken by mouth or vaginally, did not lower post-antibiotic yeast symptoms.
Urinary tract
In 252 postmenopausal women with repeat UTIs, GR-1 with RC-14 was compared with a daily antibiotic for a year. The probiotic was not as effective as the antibiotic, but it did not raise antibiotic resistance.
Vaginal flora
In 72 postmenopausal women, 14 days of oral GR-1 with RC-14 improved a standard vaginal flora score in 60% vs 16% on placebo.
Pregnancy
In 110 pregnant women carrying group B strep late in pregnancy, 43% tested negative after taking GR-1 with RC-14, compared with 18% on placebo. Another strain, HN001, was studied from early pregnancy in 423 women, looking at blood sugar, mood after birth and eczema in their babies.
Gut
A review of 12 trials of the strain GG found fewer cases of diarrhea during antibiotic use (12% vs 22%).
Studies
Human study tested in people Lab study a starting point, not proof
Studies on other strains of this species
Vaginal flora score improved in 60% vs 16%
Petricevic 2008 · Source
Yeast on culture at 4 weeks: 10% vs 39%
Martinez 2009, Letters in Applied Microbiology · Source
43% tested negative vs 18% on placebo
Ho 2016, Taiwanese Journal of Obstetrics and Gynecology · Source
Adding probiotics to antibiotics raised cure rates modestly; oral probiotics did better than vaginal ones; results varied a lot between trials
Chen 2022, Reproductive Health · Source
Diarrhea in 12% vs 22%
Szajewska 2015, Alimentary Pharmacology and Therapeutics · Source
No added benefit over antibiotics alone at 30 or 90 days
Zhang 2021, Frontiers in Cellular and Infection Microbiology · Source
Less effective than a daily antibiotic over 12 months; no rise in antibiotic resistance
Beerepoot 2012, Archives of Internal Medicine · Source
No drop in post-antibiotic yeast symptoms
Pirotta 2004, BMJ · Source
Which strain do we use?
Our strain is L. rhamnosus UALr-18 (UAS Labs). The studies on this page used other strains of this species, and results belong to the strain tested.
Is L. rhamnosus safe to take?
Probiotics are generally well tolerated in healthy adults, and the trials above reported no serious side effects. Ask a clinician first if you have a weakened immune system, a central line or catheter, a serious illness, or are pregnant or breastfeeding. In one hospital study, a few critically ill patients given strain GG developed a bloodstream infection traced to the capsules.
These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.
Last reviewed: November 2026.
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Reviewed by the Momotaro Apotheca medical team, including OB-GYNs and naturopathic doctors. Educational information, not medical advice. All ingredient research