Probiotics and erectile function
The correct statement is not "no evidence exists" — it is that the only trials that exist are placebo-free, in the wrong populations, using unnamed strains, with unreported effect sizes. That version is both true and more damning, and it survives the obvious counter-search.
The erectile-function evidence, stated at the strength it actually holds. The headline verdict here is the second version: the first was an absolute that a 240-man trial destroyed before this page was ever published, which is why the registry scope is stated in its own second paragraph.
Erectile and sexual function
ClinicalTrials.gov holds zero registered probiotic∩ED studies, independently reproduced on 29 July 2026 (cond=erectile dysfunction + intr=probiotic = 0; + intr=Lactobacillus = 0; the same controls returned 2,786 and 728, so the API works). But ClinicalTrials.gov is not a worldwide registry, and at least two 2026 randomised trials in men did measure the International Index of Erectile Function.
The largest of them is a 240-man randomised trial, and it cannot be used. Taghavi 2026: 119 versus 121 men with mild-to-moderate depression on escitalopram, 2 months, IIEF at baseline and end, reporting "Sexual function improvements were significantly higher in the intervention group across all domains… (all P < .05)" (PMID 42059569 (opens in a new tab); IRCT20160524028038N14). The authors' own limitations list "absence of placebo" — this is escitalopram versus escitalopram plus probiotic, wide open to expectancy effects. The population is SSRI-treated depressed men, not men with primary ED. It is a single Iranian clinic. The product's strains and CFU doses are unnamed, and no IIEF effect sizes are reported at all, so the clinical magnitude is unverifiable. It is not a win.
The IIEF data in the prostatitis trial is uninterpretable as an efficacy claim. It is reported only as severity-band counts — probiotic "normal" 1→4 and "severe" 2→0; placebo "normal" 2→2 and "severe" 2→1. No mean scores, no p-value, no effect size, no statistical test of the comparison (PMID 39858898 (opens in a new tab)).
The Mendelian-randomisation literature that gets cited as mechanism is one finding published four times. Four papers in four journals by four author groups report near-identical odds ratios because all four reanalyse the identical pair of public datasets: MiBioGen (N=18,340, 24 cohorts, 211 taxa) for exposure and the Bovijn 2019 ED GWAS (6,175 cases / 217,630 controls) for outcome. Lachnospiraceae 1.265 / 1.27 / 1.26 / 1.264; Ruminococcaceae UCG-013 0.770 / 0.77 / 0.79 / 0.761 (PMIDs 37928685 (opens in a new tab), 37724714 (opens in a new tab), 38273056 (opens in a new tab), 39268537 (opens in a new tab)). The outcome is a biobank case definition — ICD codes, prescriptions, self-report — not IIEF-5. Weight the entire MR body as one finding. And the durable objection is not about commercial availability: MR estimates lifelong genetic liability to genus-level abundance in a European-ancestry biobank, while probiotics are specific strains taken for weeks.
There is no reproducible ED gut signature, and the best proof is a direct cross-method contradiction. Kang 2023 (43 ED versus 16 controls, IIEF-5 plus nocturnal penile tumescence) found Lachnospiraceae_FCS020 depleted in ED patients — the opposite direction to all four MR papers (PMID 37382280 (opens in a new tab)). Su 2025 (19 versus 15, shotgun metagenomics): "No significant differences in alpha diversity… no notable changes in microbiota composition" (PMID 40539109 (opens in a new tab)). Osman 2024 (28 versus 32, metatranscriptome) was null on everything — and is Viome Inc.-funded with five Viome personnel among the authors, i.e. a microbiome-testing company published a null (PMID 37316348 (opens in a new tab)).
Where this outcome sits in the 22-row table
The grade is assigned on the hub’s 22-row table and argued above. The row is reproduced here unchanged, so the grade a reader quotes from this page is the same grade the table carries. What a grade measures is set out under how the grades work: it is a statement about the strength of the evidence for a named strain, never a statement that a product does anything.
| # | Outcome | Best grade at strain level | The strain, and the trial behind it | Buyable at the dose that was studied? |
|---|---|---|---|---|
| 16 | Erectile and sexual function | Grade F for **Erectile and sexual function** — nothing qualifies | — | Nothing qualifies |
The strains named above, and the labels in this audit that print them
Every row below is a line on a printed supplement panel, read off that product’s own teardown. A panel printing a designator is a fact about the panel. It is not evidence that the product was tested, that it delivers the amount that was studied, or that the strain does anything — several of the paragraphs above say in terms that it does not, and the dose is unknowable wherever the panel gives no per-organism quantity.
- L. casei DG®, the strain in the only IIEF-reporting prostatitis trial
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Not printed on any panel this audit has transcribed.
Read next
- Probiotics and testosterone in men: the whole chain, end to end The claim starts in one mouse study, and the same strain then failed in men in a trial run by the company that sells it. Every link in the chain.
- Probiotics for the prostate: every trial, and what none of them shows No human randomised trial of any probiotic strain in men with benign prostatic hyperplasia is indexed in PubMed. What exists instead, in full.
- Probiotics, male fertility and semen parameters The only male-specific outcome in the corpus with repeated positive human data — and it is still Grade C, and still not sold in this market.
- The evidence hub All 22 outcomes in one table, the strain × outcome table, and every other outcome page.
- What to buy, and what not to The verdict, the five reasons a man arrives here, and the products ranked by how much their labels disclose. Two of the five reasons end in nothing.