Lactobacillus rhamnosus (often misnamed as Lactococcus rhamnosus) is a probiotic strain with scientific evidence supporting its use in the management and prevention of certain forms of vaginitis, particularly bacterial vaginosis (BV) and vulvovaginal candidiasis (VVC). The rationale for its use is based on the fact that healthy vaginal microbiota are dominated by Lactobacillus species, which help maintain an acidic environment (low pH) and inhibit the growth of pathogenic organisms.

Several randomized controlled trials and meta-analyses have evaluated the efficacy of L. rhamnosus, usually alongside L. reuteri, in both oral and intravaginal formulations. Results suggest that supplementation can help restore the normal vaginal flora, reduce recurrence rates of BV and VVC, and improve clinical outcomes when used as an adjunct to standard antifungal or antibiotic therapies. Mechanistically, L. rhamnosus produces lactic acid and bacteriocins, which suppress pathogens, and can adhere to vaginal epithelial cells, enhancing colonization and competitive exclusion of harmful microbes.

However, while the evidence is promising, it is not uniformly robust across all studies, and variations in study design, probiotic strains, dosages, and treatment durations make definitive conclusions challenging. Clinical guidelines sometimes recommend probiotics as adjunctive therapy, but not as a primary treatment. Therefore, the scientific evidence supporting L. rhamnosus for vaginitis is moderate (evidence rating: 3/5).