• Summary
• The Trial That Was Not Run
• The Evidence
  • Animal-Model Causation
  • Human Strain-Level Characterization
  • Human Observational Confirmation
• The Trial That Should Be Run
• The Timeline Problem
  • Drug Cost Comparison
• Why This Matters
• References

[Boom, I’m back, actually, I’ve been publishing a LOT of literature which has kept me away from articles for a few days. This might be one and done on the Clear Evidence No Trials, but you know me…always writing. What we have here is a case of a study almost ten years old that shows that antifungals help IBS. YET….NO TRIAL has ever been done? That might have to do with the cost of a generic antifungal being less than a dollar a day, while some of the alternatives are 100x that, but I’m just guessing of course…]

§Summary

No randomized controlled trial of antifungal therapy versus placebo has been published in irritable bowel syndrome (IBS) patients stratified by mycobiome profile, despite rat-model causation established in 2017 and human strain-level phenotypic characterization published in 2021. The absence is conspicuous. The evidence is mechanistic, specific, and directly actionable. The drug is generic, inexpensive, and has decades of human safety data. The patient population is enormous. However, the trial has not been run — despite the foundational 2017 causation paper accumulating more than 240 citations in the literature as of April 2026, and despite observational confirmation from multiple independent human cohorts in the years since. This paper documents what the evidence shows, what the trial should look like, and why it has not happened. [Money, Money, Money, Money…]

§The Trial That Was Not Run

Nobody has run the trial. [Hmm…ok] The trial in question would give IBS patients a cheap generic antifungal pill for a fixed period, give another group of IBS patients a look-alike sugar pill, and then compare how the two groups feel at the end. Basic stuff. The kind of study that gets run in medical schools all over the world, every year, for every promising treatment anyone bothers to investigate.

The measurement they would use is straightforward: how much pain does your gut generate in response to normal stimulation? IBS patients feel that pain at a much lower threshold than healthy people. That is the whole complaint. That is what brings them to the clinic. You check it before treatment, you check it after treatment, and you see whether the drug changed anything.

The reason to run it has been sitting on the shelf since 2017, when a research team showed that fungi in the gut caused IBS-like symptoms in rats. In 2021, another team showed that IBS patients actually have different fungal populations in their guts than healthy people do. Since then, more studies have come in saying the same thing from different angles. The drug you would give them has been off-patent and cheap since 2004 — about fifteen cents a day at a US pharmacy.

That trial has not been done. [Weird, right? Evidence it works, yet…]

And yet no entry exists in any of the trial registries where scientists post these studies before they start. No completed study has been published. Nothing is pending, as far as the searchable record shows.

The question has simply not been investigated. [Seems like nobody cares about solving the problem cheaply]

§The Evidence

§Animal-Model Causation

Botschuijver and colleagues (2017), working in the van den Wijngaard group at Amsterdam, established direct fungal-causation of visceral hypersensitivity in rats. Maternally separated rats (a validated stress-induced IBS-analog model) developed both mycobiome dysbiosis and visceral hypersensitivity relative to non-handled controls. Treatment with fluconazole and nystatin reduced visceral hypersensitivity. Fecal microbiota transfer from dysbiotic rats transmitted the hypersensitivity phenotype, while transfer from normally-sensitive controls did not. The study was published in Gastroenterology, the flagship journal of the American Gastroenterological Association, and has accumulated more than 240 citations in the scientific literature as of April 2026. [So, LOTS of people are citing it. That is a goodly number for a paper]

The result established a specific, testable, causal claim: ffungi in the gut, when out of balance, make gut nerves oversensitive. Treat the fungi, the oversensitivity goes away. The authors stated the intervention implication explicitly. From the paper’s own conclusion:

“In studies of rats, we found fungi to promote visceral hypersensitivity, which could be reduced by administration of fungicides, soluble β-glucans, or a SYK inhibitor. The intestinal fungi might therefore be manipulated for treatment of IBS-related visceral hypersensitivity.”

The authors named the intervention. The trial was not run. [So far… after 9 years]

§Human Strain-Level Characterization

Sciavilla and colleagues (2021) looked at the Candida albicans in 20 IBS patients and compared it to the C. albicans in 18 healthy controls. A few things stood out.

Each IBS patient carried their own distinct population of the organism, with no shared strain spreading between patients. The disease isn’t contagious in the usual sense — each host was independently selecting for a problem subset from within their own resident fungal pool.

Eighty-two percent of the IBS samples had shifted into a more invasive form, compared to fifty-four percent in healthy controls. The invasive form was demonstrably better at punching through tissue in the lab.

And the punchline: the IBS version was more susceptible to fluconazole than the healthy-control version, not less. The worse the organism behaved in the gut, the more readily it died to the cheapest standard antifungal on the pharmacy shelf.

The authors concluded, in their own discussion, that the more invasive fungi could contribute to the pain associated with IBS. From the Sciavilla discussion:

“We could hypothesize that fungal isolates with peculiar virulent and invasive traits could contribute to visceral hypersensitivity associated to IBS… we could speculate a putative clonal expansion of C. albicans strains in IBS.” [basically, these people had a version of C. albicans that was measurably worse on the gut than the other people…same DNA, btw, just operating in a different stuck state, but that’s another paper]

They stopped short of recommending an intervention trial.

Worth noting who paid for this: a single internal research grant from the University of Bologna. Not a major consortium, not a pharmaceutical sponsor, not an NIH or Horizon Europe award. The human phenotype that sharpens the 2017 rat finding into a directly testable clinical target was produced on what amounts to departmental funding from an Italian university. The work is published open access under CC BY 4.0. Anyone can read it, cite it, and build on it. The infrastructure for the next step exists. The permission to use the findings exists. [But, you can’t make money on a generic drug finding that helps millions of people]

§Human Observational Confirmation

Additional human cohort studies have confirmed mycobiome dysbiosis in IBS across independent populations. Hong et al. (2020, Neurogastroenterology & Motility) documented gut fungal dysbiosis and altered bacterial-fungal interactions specifically in diarrhea-predominant IBS, with Candida abundance positively correlated to bloating severity and anxiety scores. Das et al. (2021, Scientific Reports) characterized the fecal mycobiome in IBS and documented systematic compositional differences from healthy controls.

The observational pattern is consistent. The intervention trial is absent.

§The Trial That Should Be Run

The study isn’t complicated. Randomize IBS patients to fluconazole or placebo for six weeks. Measure gut pain sensitivity before and after. Follow up at twelve weeks.

A six-week course of generic fluconazole costs about ten to forty dollars per patient. The entire trial — drugs, sequencing, clinical monitoring, the works — would run in the low seven figures. That’s less than 1 percent of what it cost to develop any branded IBS drug approved in the last twenty years. [Sounds like it is worth 1%, huh? I mean if it fails, you lose basically nothing…except all the profits on the more expensive one]

§The Timeline Problem

Between 2000 and 2019, the U.S. Food and Drug Administration approved at least seven branded drugs for the treatment of IBS or IBS-associated symptoms. Each represented hundreds of millions of dollars in development cost. Each was developed against a patentable novel molecule or novel indication. None were tested against a generic antifungal comparator.

§Drug Cost Comparison

[

The cost delta is the essential part of the table. Generic fluconazole at standard dosing costs roughly $15–35 per month at United States retail pharmacies. Its branded IBS-indicated competitors cost between $300 and $2,650 per month. The cheapest branded IBS drug in active use costs approximately ten times what a full month of the generic antifungal costs. The most expensive costs roughly one hundred times as much. A successful fluconazole-IBS trial would introduce a comparator priced at 0.5 to 10 percent of the existing market — for a condition that collectively generates billions of dollars in annual branded-drug revenue. [I doubt they will be happy with me]

Fluconazole became available as a generic in the United States in approximately 2004, following the expiration of core Pfizer patents on the molecule. By the time Botschuijver and colleagues published their rat-model causation study in June 2017, fluconazole had been an off-patent commodity drug for thirteen years.

The 2017 causation finding arrived in the middle of the most active period of branded IBS-drug approvals in the history of the indication. Eluxadoline and rifaximin had been approved for IBS-D two years earlier. Plecanatide’s IBS-C indication was approved in January 2018, seven months after Botschuijver. Tenapanor was in late-stage trials. A successful fluconazole-IBS trial in 2017 would have competed directly with every one of these products, and would have done so at a fraction of the per-patient drug cost.

No commercial sponsor had any incentive to fund such a trial. Pharmaceutical development is structurally oriented toward patent-protected molecules with defensible market exclusivity. A generic-drug comparator trial — especially one that might demonstrate equivalent or superior efficacy to a branded competitor at 1/100th the monthly cost — offers no return on investment. Academic and public-sector funding for generic-drug repurposing trials, while it exists, is chronically underfunded relative to novel-molecule development. The U.S. National Institutes of Health budget for this type of work has been flat or declining in real terms across the relevant period. [You know those cuts the government made recently? NIH was slammed. These are the people on your side getting money cut that could help you.]

The finding was not suppressed. It was ignored. Sure, it was cited and confirmed observationally, but it never translated into an obvious intervention trial. The incentive structure reliably produces this outcome whenever strong evidence supports a cheap-generic intervention for a condition already served by a branded drug market. The mechanism is economic, not conspiratorial. The result is a nine-year silence on a trial that should have taken two years to run.

§Why This Matters

IBS affects roughly 10–15 percent of the global adult population. Annual direct and indirect costs in the United States alone are estimated in the tens of billions of dollars. Current pharmacologic options produce modest symptom improvement in a subset of patients and carry adverse event profiles that range from nuisance-level to severe. Several IBS drugs have been restricted or withdrawn post-approval due to safety signals.

A trial of a cheap, safe, generic antifungal in mycobiome-dysbiotic IBS patients is one of the lowest-cost, lowest-risk, highest-potential-impact clinical research questions currently identifiable in gastroenterology. The evidence base supporting it is stronger than the evidence base that supported several approved branded competitors at the time of their regulatory submission. The trial has not been run. [I’m saying that a lot, huh?]

The framework within which this finding is most readily interpreted — that Candida albicans operates as a regulated component of host physiology rather than an incidental opportunist — has been developed elsewhere [1]. The interpretive framework is not required to acknowledge the central observation of this paper: the evidence is clear, the trial is obvious, and the trial has not been run.

Any interested investigator, sponsor, or regulatory body is free to run it. [And yes, I’m posting the protocol, so they get to reference me if they design one someday]

Original Article DOI: https://doi.org/10.5281/zenodo.19645403

§References

Botschuijver, S., Roeselers, G., Levin, E., et al. (2017). Intestinal fungal dysbiosis is associated with visceral hypersensitivity in patients with irritable bowel syndrome and rats. Gastroenterology, 153(4), 1026–1039. https://doi.org/10.1053/j.gastro.2017.06.004

Das, A., O’Herlihy, E., Shanahan, F., O’Toole, P. W., & Jeffery, I. B. (2021). The fecal mycobiome in patients with irritable bowel syndrome. Scientific Reports, 11, 124. https://doi.org/10.1038/s41598-020-79478-6

Hong, G., Li, Y., Yang, M., et al. (2020). Gut fungal dysbiosis and altered bacterial-fungal interaction in patients with diarrhea-predominant irritable bowel syndrome: An explorative study. Neurogastroenterology & Motility, 32(11), e13891. https://doi.org/10.1111/nmo.13891

Sciavilla, P., Strati, F., Di Paola, M., et al. (2021). Gut microbiota profiles and characterization of cultivable fungal isolates in IBS patients. Applied Microbiology and Biotechnology, 105(8), 3277–3288. https://doi.org/10.1007/s00253-021-11264-4

[1] Craddock, J. (2025). Candida albicans as a Biochemical Computer. Zenodo. https://doi.org/10.5281/zenodo.19337525

Clear Evidence, No Trial is a series published by Redacted Science documenting clinical research questions where mechanistic evidence is established, the intervention is specific and available, and the required randomized trial has not been conducted. Each entry names the problem, the treatment, and the structural reasons the trial has not happened. The series makes no claim that its underlying framework must be accepted; the documented absences stand on their own terms.