Probiotics for Kidney Stones

Probiotics have not been shown to prevent kidney stones. The idea is that oxalate-degrading bacteria in the gut leave less oxalate to reach the urine, and about 75% of urinary stones contain oxalate (Siener 2013, Kidney Int). But in placebo-controlled trials of lactic acid bacteria mixes in people with calcium stones or high urine oxalate, urinary oxalate fell no more than on placebo: in 20 stone formers (Goldfarb 2007), in a three-arm trial on a controlled diet (Lieske 2010), and in 100 recurrent stone formers, of whom 64 finished (Tavasoli 2021).

Two small trials point the other way. A synbiotic (probiotic plus prebiotic) lowered urinary oxalate over 12 weeks in 44 overweight adults with high urine oxalate (Maddahi 2026), and an Oxalobacter formigenes preparation cut hyperoxaluria more than potassium magnesium citrate over one month in 80 stone formers (Jairath 2015). Neither has been repeated, and no trial has counted new stones. A 2025 systematic review concluded the evidence does not support these probiotics for lowering urinary oxalate or preventing recurrence (Bhardwaj 2025). We rate it insufficient rather than a firm no only because stones themselves have never been measured.

Oxalate absorbed from food is passed in urine, where it can combine with calcium to form crystals. Some gut bacteria use oxalate as food. The best known, Oxalobacter formigenes, is thought to lower the amount of oxalate in the gut that is available for absorption; in 37 calcium oxalate stone formers, those carrying it had lower urinary oxalate on a standardised diet and much lower plasma oxalate (1.70 vs 5.79 µmol/L) (Siener 2013, Kidney Int).

Lactic acid bacteria, the Lactobacillus and Bifidobacterium species in most supplements, were tried because some degrade oxalate in vitro (Goldfarb 2007). Their ability varies widely by strain: in one pilot, L. acidophilus, S. thermophilus and B. infantis degraded oxalate well in the lab, while L. plantarum and L. brevis managed only a modest amount (Campieri 2001).

Swallowed bacteria have to survive and settle in the gut to keep working. In the largest placebo-controlled trial, the probiotic strains were not found in the stool of most participants, and the authors suggested this may explain the null result (Tavasoli 2021). In another trial faecal lactobacilli did rise, yet urinary oxalate still did not fall (Lieske 2010). In a stool study of recurrent stone formers, Lactobacillus and Bifidobacterium levels were not linked to stones or urine oxalate at all; only O. formigenes was (Tavasoli 2020).

People naturally colonised with O. formigenes were 70% less likely to be recurrent calcium oxalate stone formers (odds ratio 0.3) in a case-control study of 506 adults, yet their urinary oxalate was no different, which the authors called surprising (Kaufman 2008). That association describes bacteria people already carry, not a capsule, and it doesn't show that adding bacteria changes stone risk. Open studies in healthy volunteers suggest any benefit concentrates in people who absorb a lot of oxalate (Okombo 2010; Al-Wahsh 2012).

There is no established probiotic dose for kidney stones. The negative placebo-controlled trial in 20 stone formers used 3.6 g a day of a four-species lactic acid bacteria granulate for 28 days (Goldfarb 2007), and the healthy-volunteer study used 2.6 g a day for 5 weeks (Siener 2013, J Transl Med). The positive uncontrolled pilot used a very high 8 x 10^11 freeze-dried bacteria a day for 4 weeks (Campieri 2001). The Oxalobacter trial in stone formers used 700 million bacteria twice a day for one month (Jairath 2015), and the synbiotic trial gave capsules twice daily for 12 weeks without the dose appearing in its abstract (Maddahi 2026).

The most common probiotic bacteria are Lactobacillus and Bifidobacterium species (NCCIH), the group that failed in placebo-controlled trials. Oxalobacter formigenes was tested as an investigational product in trials (Hoppe 2011; Hoppe 2017). If you decide to try one anyway, the last step below explains how to test it without fooling yourself.

In a double-blind trial in 20 adults with calcium stones and idiopathic hyperoxaluria, a lactic acid bacteria mix had no effect: urinary oxalate went from 73.9 to 72.7 mg a day on placebo and from 59.1 to 55.4 mg on the probiotic (Goldfarb 2007). A three-arm double-blind trial in people with mild hyperoxaluria, all on a controlled diet, found neither a probiotic nor a synbiotic reduced urinary oxalate or calcium oxalate supersaturation, even though faecal lactobacilli rose (Lieske 2010).

The largest trial randomised 100 recurrent calcium stone formers with high urine oxalate to L. acidophilus plus B. lactis or placebo for 4 weeks; 64 finished. Urinary oxalate fell by a similar amount in both groups (57.21 to 49.44 mg a day on the probiotic, 56.43 to 50.47 mg on placebo; P = .776) (Tavasoli 2021). In an uncontrolled study of 20 healthy adults on an oxalate-rich diet, a lactic acid bacteria preparation lowered neither urinary nor plasma oxalate (Siener 2013, J Transl Med).

A 2026 double-blind trial in 44 overweight or obese adults with high urine oxalate found a synbiotic taken twice daily for 12 weeks lowered urinary oxalate compared with placebo (P = .001), but no other stone-risk marker changed and the abstract gives no effect size (Maddahi 2026). A randomised trial in 80 people with calcium oxalate stones found hyperoxaluria fell from 82.5% to 15% after a month of Oxalobacter formigenes, against 77.5% to 37.5% on potassium magnesium citrate, with no placebo group (Jairath 2015).

The early encouraging results came from small open studies without a control group: urinary oxalate fell from 55.5 to 33.5 mg a day in 6 stone formers (Campieri 2001), and by 19-24% in 10 people with fat malabsorption before rebounding at the highest dose (Lieske 2005). In 14 stone formers on an oxalate-rich diet, adding L. casei and B. breve changed urinary oxalate from 35 to 33 mg a day, not a significant difference (Ferraz 2009). An uncontrolled study combining three probiotic strains with potassium citrate and magnesium after stone surgery reported less crystalluria, but the citrate could explain that (Vittori 2024).

A single dose of live O. formigenes colonised all 22 healthy adults in a 2025 study, and stool and urine oxalate fell by 54% and 14%; colonisation was lost in 11 people, 9 of whom had taken antibiotics (Fargue 2025). In primary hyperoxaluria, a rare genetic disease that causes recurrent stones, two double-blind trials found an O. formigenes product did not lower urinary oxalate (Hoppe 2011; Hoppe 2017), even though in the second it reached the gut (Hoppe 2017), and a meta-analysis of five trials in 208 patients confirmed no effect (Khan 2025).

Part of the interest in probiotics comes from studies linking antibiotics to stones. In UK records, five antibiotic classes taken 3-12 months earlier were linked to higher odds of stones, for example an odds ratio of 2.33 for sulfa drugs (Tasian 2018), and in US nurses, 2 or more months of antibiotics in mid-life was linked to more stones (hazard ratio 1.48) (Ferraro 2019).

A Minnesota study of first-time symptomatic stones found the link shrank after adjustment and disappeared after excluding people with earlier urinary symptoms (odds ratio 1.04), suggesting undiagnosed stones were being treated with antibiotics (Thongprayoon 2023). None of these studies tested probiotics, and a 2017 review called the probiotic trials disappointing (Lieske 2017).

In these trials probiotics were well tolerated: three people on the lactic acid bacteria mix reported mild constipation (Goldfarb 2007), no serious adverse events were reported with Oxalobacter in primary hyperoxaluria (Hoppe 2011), and a meta-analysis found no excess of adverse events (Khan 2025). The NIH notes that probiotics have a long history of apparently safe use in healthy people, but few studies have examined safety in detail (NCCIH).

Harms are more likely in people with severe illness or weakened immune systems, and some products have been found to contain microorganisms not listed on the label (NCCIH). Severe or fatal infections have been reported in premature infants given probiotics, and the FDA has warned health care providers about this risk (NCCIH). For people with stones, the bigger risk is indirect: using a probiotic instead of the fluids, diet changes and prescribed treatments that guidelines recommend (Hughes 2020).

Probiotics have few documented drug interactions. The practical issues are antibiotics, which can clear the bacteria (in the Oxalobacter study, 9 of 11 people who lost colonisation had taken antibiotics) (Fargue 2025), immune-suppressing treatment, which raises infection risk (NCCIH), and the temptation to swap a probiotic for proven stone prevention.