Lactobacillus rhamnosus GR-1
The most clinically studied probiotic strain for women's vaginal health, shown to colonize the vaginal tract via oral supplementation and support a healthy Lactobacillus-dominant microbiome.
Lactobacillus rhamnosus GR-1
Lactobacillus rhamnosus GR-1 is a specific probiotic strain isolated from the female urogenital tract by Dr. Gregor Reid at the University of Western Ontario. It is the single most studied probiotic strain for vaginal and urinary tract health, with over 25 years of continuous clinical research. The "GR" in its designation stands for Gregor Reid, the researcher who characterized its unique properties.
What makes GR-1 exceptional is not its species name but its strain-specific capabilities. Other strains of L. rhamnosus, such as the well-known GG strain, do not share GR-1's ability to colonize the vaginal tract. Strain specificity is fundamental in probiotic science: the clinical evidence for GR-1 does not transfer to generic "L. rhamnosus" products.
How It Works
L. rhamnosus GR-1 reaches the vaginal tract through a remarkable biological pathway. When taken orally, the bacteria survive gastric transit, colonize the intestinal tract, and migrate to the vaginal epithelium via the perineum. This oral-to-vaginal colonization route has been confirmed through culture and molecular identification studies.
Once established in the vaginal tract, GR-1 exerts its protective effects through multiple mechanisms. It produces biosurfactants that inhibit the adhesion of pathogenic organisms including Gardnerella vaginalis and Candida albicans to vaginal epithelial cells. It also produces hydrogen peroxide and bacteriocins that directly suppress pathogenic growth.
GR-1 promotes a Lactobacillus-dominant vaginal microbiome, which is the hallmark of vaginal health. A healthy vaginal microbiome maintains an acidic pH (3.8-4.5) through lactic acid production, creating an environment inhospitable to most pathogens. When this Lactobacillus dominance is disrupted, conditions such as bacterial vaginosis, vulvovaginal candidiasis, and urinary tract infections become more likely.
The strain works synergistically with L. reuteri RC-14, and the two are almost always studied together. RC-14 complements GR-1 by producing signaling molecules that modulate the local immune response and further inhibit pathogen adhesion.
Clinical Evidence
Reid et al. (2003) conducted a landmark randomized controlled trial demonstrating that oral supplementation with L. rhamnosus GR-1 and L. reuteri RC-14 significantly restored a normal vaginal flora in women with bacterial vaginosis and vulvovaginal candidiasis. The probiotic group showed conversion to a Lactobacillus-dominant flora at rates significantly higher than placebo.
Anukam et al. (2006) compared the GR-1/RC-14 combination to metronidazole (the standard antibiotic treatment) for bacterial vaginosis. The probiotic combination achieved cure rates comparable to the antibiotic, with the added benefit of restoring healthy vaginal flora rather than simply eliminating pathogens.
A 2009 Cochrane-style review by Falagas et al. evaluated probiotics for UTI prevention and found that L. rhamnosus GR-1 in combination with L. reuteri RC-14 reduced the recurrence of urinary tract infections, particularly in premenopausal women with a history of recurrent UTI.
Martinez et al. (2009) showed that daily oral supplementation with GR-1 and RC-14 for 2 months significantly increased vaginal Lactobacillus counts and improved the Nugent score (a clinical measure of vaginal health) in healthy postmenopausal women.
Vujic et al. (2013) demonstrated in a double-blind RCT that L. rhamnosus GR-1 and L. reuteri RC-14 taken alongside standard antibiotic therapy for bacterial vaginosis significantly improved cure rates compared to antibiotics alone.
Dosing and Safety
The clinically validated dose for L. rhamnosus GR-1 is 1-15 billion CFU daily, typically taken in combination with L. reuteri RC-14. Most clinical trials used a combined dose of 2-30 billion CFU per day. Colonization of the vaginal tract typically begins within 1-2 weeks of daily oral supplementation.
L. rhamnosus GR-1 has an excellent safety profile and is classified as safe for daily, long-term use in healthy adults. It can be taken with or without food, though taking it on an empty stomach (30 minutes before breakfast) may optimize survival through the acidic gastric environment.
Contraindications include severe immunosuppression, critical illness requiring intensive care, and short bowel syndrome. Individuals with central venous catheters should consult their healthcare provider, as there are rare case reports of Lactobacillus bacteremia in severely immunocompromised patients, though none specifically involving GR-1.
Mild gastrointestinal adjustments (bloating, gas) may occur during the first few days of supplementation and typically resolve within a week as the microbiome adapts.
Ankhora Products Containing L. rhamnosus GR-1
Flora Shield provides 15 billion CFU of L. rhamnosus GR-1 alongside L. reuteri RC-14 and L. crispatus CTV-05 for comprehensive vaginal and digestive microbiome support.
Women's Probiotic Complex includes GR-1 as a foundational strain in a multi-species formulation designed for everyday women's health maintenance.
*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.