What Do Probiotics Do for Women? Trial Results by Outcome

In trials, live cultures ("probiotics" is the search word) have done four measurable things for women. After antibiotics for bacterial vaginosis (BV), recurrence was 14.8% against 25.5% across ten trials of 1,234 women. Added to antifungals for thrush, they gave a small short-term gain and no benefit at three months. For recurrent urinary infections, the Cochrane review of nine trials found no significant effect. Taken alongside antibiotics, they were associated with less antibiotic-associated diarrhoea across 63 trials of 11,811 people (relative risk 0.58).^{1, 2, 3, 4} None of that is a cure. Antibiotics and antifungals are the treatments for BV, thrush and UTIs, no live culture has an authorised health claim in Great Britain, and every figure here is a trial finding.^{5, 6} This is the women's explainer in the Wellgard guide to what causes BV; choosing a capsule is on what's the best probiotics for women's health?

Evidence at a glance

• Trials: ten BV-recurrence trials pooled in 2022 (1,234 women); ten thrush trials in the 2017 Cochrane review (1,656 women); nine UTI trials (735 people); 63 antibiotic-diarrhoea trials (11,811 people).^{1, 2, 3, 4}
• Largest single UK trial: 304 pregnant women, oral two-strain capsules to delivery; BV at 18 to 20 weeks in 15% against 9% on placebo, no significant difference.⁷
• Strongest measured outcome: BV recurrence of 14.8% with live cultures after antibiotics against 25.5% without (relative risk 0.55).¹
• Not tested: "balance", wellbeing, taste or libido in healthy women; no trial has compared one women's capsule with another.

Sources checked on 16 October 2026.

What does probiotics do for a woman? The BV evidence

A healthy vagina is dominated by lactobacilli: in 56 women with that flora, the average pH was 3.5 and the fluid held about 1% lactic acid (two of the study's authors worked for a company developing vaginal products).⁸ BV is the loss of that dominance, and the NHS says it "is usually treated with antibiotic tablets or gels or creams" from a GP or sexual health clinic.⁶ The trials ask a narrower question: once an antibiotic has cleared BV, do live cultures help lactobacilli stay in charge?

The 2022 pooled analysis took ten randomised trials, 1,234 women, in which live cultures followed a standard antibiotic course and BV was reassessed after at least one menstrual cycle: recurrence was 14.8% against 25.5% (relative risk 0.55), the result held when high-bias trials were removed, and route, dose, days of use and number of species made no measurable difference.¹ Every trial gave the cultures after or alongside the antibiotic, never instead of it. Can I get rid of BV by taking probiotics? sets out the ten trials one by one.

How do probiotics help women's health? Thrush, UTIs and antibiotic diarrhoea

Thrush. The NHS says "you'll usually need antifungal medicine to get rid of thrush".⁹ In the Cochrane review of ten trials in 1,656 non-pregnant women, live cultures were always added to an antifungal: short-term clinical cure was more likely (relative risk 1.14, low quality), relapse at one month less likely (0.34, very low quality), and there was no benefit at three months.² For thrush brought on by antibiotics the one large trial is a null: in 278 Australian women, neither oral nor vaginal lactobacillus taken through an antibiotic course reduced it.¹⁰

Urinary infections. The NHS counts a UTI as recurrent at "2 UTIs in 6 months (or 3 within 12 months)" and says to see a GP; a pharmacist "can give the same medicines as a GP".¹¹ In the 2015 Cochrane review, nine small trials with 735 people found no significant benefit from live cultures; against placebo, six trials with 352 people gave a relative risk of 0.82 for recurrent UTI (confidence interval 0.60 to 1.12); the authors said the trials were too small and poorly reported to rule a benefit in or out.³ Why do I keep getting UTIs? has the NHS pathway and the cranberry evidence.

Antibiotic-associated diarrhoea. The firmest result for live cultures in anyone. Across 63 randomised trials with 11,811 people, live cultures taken with antibiotics were associated with less diarrhoea (relative risk 0.58; 13 people taking them for one fewer case), although strains were poorly documented.⁴ A 2021 analysis of 42 adult trials (11,305 people) agreed, graded moderate certainty, with higher doses doing better and the benefit confined to people at moderate or high baseline risk.¹² The culture was taken during the course, not after it.

How do women's probiotics help, and what makes a capsule "women's"?

"Women's" on a pack describes the evidence the species were chosen for, not a different kind of organism. The species are the lactobacilli and bifidobacteria of the gut trials; what varies is which strains are in the capsule and where their evidence was gathered. Whether oral capsules reach the vagina is species by species, on are probiotics good for your vagina? In Great Britain no live culture has an authorised health claim and "probiotic" is itself read as a claim, so a lawful pack states the species, the count and the date it is guaranteed to, and promises nothing; "pH balance" and "intimate health" cannot lawfully be promised either.⁵ In pregnancy the evidence is a null: in 304 UK women taking oral two-strain capsules from early pregnancy to delivery, BV at 18 to 20 weeks did not differ (15% against 9%), with no safety problems; ask a GP or midwife before any supplement in pregnancy.⁷

Do probiotics cause weight gain, and what happens when you start taking them?

The weight-gain idea traces to a 2012 analysis that pooled 17 human trials with 65 animal studies and found Lactobacillus acidophilus associated with a small weight gain across species (standardised difference 0.15).¹³ In the trial that tested the question directly, 53 women aged 19 to 33 took a two-strain capsule or placebo for six weeks and no body measure changed in either group.¹⁴ Does acidophilus cause weight gain? has the full record. On starting, trials report mild stomach symptoms in some women; serious adverse events were no more common than with placebo (relative risk 0.80 in the two thrush trials that counted them).² The adjustment period is on can probiotics make you feel worse before better? Live cultures pass through rather than settle: in 117 people followed for eight weeks, stool levels of the strain "declined and approached baseline once dosing ceased", so a daily capsule is a daily habit.¹⁵

What we don't know

• No trial has compared one women's live-culture capsule with another, so none can be called best.
• No trial has measured what live cultures do for a healthy woman with no diagnosis.
• The ten BV trials used different species, routes and durations; the pooled analysis could not say which mattered.
• No trial has compared timings of a live culture against an antibiotic dose.

Frequently asked questions

Are there signs you need probiotics, and should every woman take them?

No test or symptom list points to needing live cultures, and no trial has given them to healthy women to see what changes; the evidence is for after antibiotics for BV, alongside antifungals for thrush, and during an antibiotic course. The NHS says anyone with an existing health condition or a weakened immune system should talk to a doctor first.¹⁶ Daily use is on how do I take women's probiotics?

How long do probiotics take to work, and how long do they stay in your system?

The BV trials reassessed women after at least one menstrual cycle and the thrush trials at one and three months.^{1, 2} Cultures are found while taken and fall back to baseline within weeks of stopping.¹⁵ How long should I take probiotics? has the durations by outcome.

What is the best probiotic for women's pH balance?

No label may claim pH balance in Great Britain.⁵ pH is a measured outcome: lactobacilli hold a healthy vagina at around 3.5, and the trials that counted them are on are probiotics good for your vagina?⁸

Do probiotics get rid of smell?

One three-month trial of 89 women with BV reported less smell of discharge on oral or vaginal L. crispatus capsules, with no figures and a manufacturer among its authors; a fishy smell is BV until a swab says otherwise.^{17, 6} What probiotics make your vagina smell better? covers which smell is which.

Is apple cider vinegar a probiotic?

No trial has tested it for any outcome on this page; see does apple cider vinegar improve gut health?

Sources

1. Chieng WK, et al. Probiotics, a promising therapy to reduce the recurrence of bacterial vaginosis in women? A systematic review and meta-analysis of randomized controlled trials. Frontiers in Nutrition, 2022. Pooled analysis of 10 trials, 1,234 women. PubMed 36204368.
2. Xie HY, et al. Probiotics for vulvovaginal candidiasis in non-pregnant women. Cochrane Database of Systematic Reviews, 2017. Pooled analysis of 10 trials, 1,656 women. PubMed 29168557.
3. Schwenger EM, Tejani AM, Loewen PS. Cochrane Database of Systematic Reviews, 2015. Pooled analysis of 9 trials, 735 people. PubMed 26695595.
4. Hempel S, et al. JAMA, 2012. Pooled analysis of 63 trials, 11,811 people. PubMed 22570464.
5. Department of Health and Social Care. Great Britain nutrition and health claims register (no authorised health claim for any live culture). Updated 19 May 2026. gov.uk.
6. NHS. Bacterial vaginosis. Page last reviewed 19 June 2026. nhs.uk/conditions/bacterial-vaginosis.
7. Husain S, et al. Effects of oral probiotic supplements on vaginal microbiota during pregnancy: a randomised, double-blind, placebo-controlled trial with microbiome analysis. BJOG, 2020. Randomised trial, 304 women, early pregnancy to delivery. PubMed 30932317.
8. O'Hanlon DE, Moench TR, Cone RA. Vaginal pH and microbicidal lactic acid when lactobacilli dominate the microbiota. PLoS One, 2013. Observational, 56 women; two authors employed by a company developing vaginal products. PubMed 24223212.
9. NHS. Thrush in men and women. Page last reviewed 28 July 2023 (review overdue). nhs.uk/conditions/thrush-in-men-and-women.
10. Pirotta M, et al. BMJ, 2004. Randomised trial, 278 women. PubMed 15333452.
11. NHS. Urinary tract infections (UTIs). Page last reviewed 11 July 2025. nhs.uk/conditions/urinary-tract-infections-utis.
12. Goodman C, et al. BMJ Open, 2021. Pooled analysis of 42 trials, 11,305 adults. PubMed 34385227.
13. Million M, et al. Comparative meta-analysis of the effect of Lactobacillus species on weight gain in humans and animals. Microbial Pathogenesis, 2012. Pooled analysis of 17 human trials and 65 animal studies. PubMed 22634320.
14. Czajeczny D, et al. Eating and Weight Disorders, 2021. Randomised trial, 53 women enrolled, 38 completed, 6 weeks; no conflict of interest declared. PubMed 32797375.
15. Charbonneau D, Gibb RD, Quigley EM. Gut Microbes, 2013. Controlled study, 117 people, 8 weeks; funding not checked. PubMed 23549409.
16. NHS. Probiotics. Page last reviewed 24 November 2022 (review overdue). nhs.uk/tests-and-treatments/probiotics.
17. Mändar R, et al. Impact of Lactobacillus crispatus-containing oral and vaginal probiotics on vaginal health: a randomised double-blind placebo controlled clinical trial. Beneficial Microbes, 2023. Randomised trial, 89 women with BV and 93 with thrush, 3 months; one author at a manufacturer. PubMed 36856121.

General information, not medical advice. Live cultures are a food supplement, not a treatment; antibiotics and antifungals are the treatments for BV, thrush and UTIs.

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