Report 039 · Supplements
A UC San Diego trial gave people a polypore mushroom supplement alongside a COVID vaccine. The press release said it improved vaccine response. The paper says it was a safety and feasibility study, and the headline result lives inside a subgroup of thirty people.
Disclosure first: this one is my own category. My company formulates and sells functional-mushroom supplements, and one of the two mushrooms in this study, Trametes versicolor, is turkey tail, which is a product I could sell you. So read what follows knowing that a positive result here would be good for my business. That is precisely why I am going to be hard on it.
The headline, from UC San Diego's own newsroom on 3 March 2026, was "Study Finds Natural Fungal Supplement Improves COVID-19 Vaccine Response." That is a strong claim, it came from a real university, and it was attached to a real randomized, double-blind, placebo-controlled trial published in a peer-reviewed journal. All of that is unusual for a mushroom supplement and all of it is to the researchers' credit. The trial is also more modest than the headline, and the gap between the two is the most useful thing in the story.
The paper is Saxe and colleagues, "Polypore mushroom mycelia as an adjunct to COVID-19 vaccination: a randomized clinical trial," published in BMC Immunology on 31 January 2026. It was registered in advance as NCT04951336, which is the right way to run a trial and worth saying out loud, because a lot of supplement research is not registered at all.
The intervention, called FoTv, was freeze-dried mycelium from two polypore fungi, Fomitopsis officinalis (agarikon) and Trametes versicolor (turkey tail), grown on brown rice. Ninety adults were randomized around their COVID vaccination, 52 to FoTv and 38 to placebo. The dose is worth pausing on: eight 500-mg capsules, three times a day, for four consecutive days. That is twelve grams a day, and then it stops. This was not a daily supplement regimen. It was a short, very large pulse timed to a vaccine.
And here is the part the press release does not carry. The authors list the trial's primary outcomes as safety, feasibility, side-effect count and severity over days 1 to 5, and antibody levels. Safety and feasibility come first because that is what a study this size can actually establish. A 90-person trial is a competent way to ask "is this stuff harmful, and can people take it as directed?" It is not built to settle whether a supplement improves immunity.
On its own terms, the safety answer was clean: no adverse events, complete participation, and treatment adherence above 95 percent. That is a real result and the trial delivered it.
The side-effect result is where the reading gets careful. Five participants were excluded as outliers, leaving 85 analyzed. Across the whole group, the interaction the authors tested came back at F(8,325) = 1.898, p = 0.060. That is a trend, not a finding, and by the conventional threshold it does not clear the bar.
The significant result appears after the group is split by whether participants had been exposed to SARS-CoV-2 before. In the COVID-naive stratum, FoTv beat placebo on side effects, F(4,112) = 2.956, p = 0.023, with the separation landing on days 3 and 5 specifically. In the previously exposed stratum there was nothing at all: F(4,212) = 0.436, p = 0.782.
Now count the people. The COVID-naive stratum was 19 on FoTv and 11 on placebo. Thirty people, unevenly split, is the population that carries the headline. The antibody findings run the same way, as an interaction with exposure status, meaning they too are statements about subgroups rather than about the trial as a whole. To their credit, the UC San Diego release does say the strongest results were in the COVID-naive participants. It just does not tell you that "the COVID-naive participants" means eleven people in the comparison arm.
The most-quoted result is that antibody levels in the naive FoTv group kept climbing over six months instead of drifting down. That sounds like durable protection. The authors are careful not to say it is, and their limitations section explains why, verbatim: "we were not able to conduct a viral neutralization assay that would have been needed to confirm that Abs were indeed neutralizing the virus."
That single sentence is the difference between an antibody number and an immune outcome. A neutralization assay is the test that asks whether the antibodies actually stop the virus. Without it you have a measurement that correlates with protection, not a demonstration of it. The authors also note they could not track actual post-vaccination infections and used antibody levels as a stand-in, and that "attrition bias may have influenced the Ab results because completers and non-completers differed with respect to age."
None of that is hidden. It is all in the paper, written plainly by the people who ran the study. It simply does not survive the trip into a headline.
The funding line matters here and is disclosed in both the paper and the university release. The trial was supported in part by a grant from Fungi Perfecti, LLC, and the mushroom mycelium used in the study was provided by Fungi Perfecti, LLC. Fungi Perfecti is Paul Stamets' company, founded in 1980, and its supplement line, Host Defense, sells exactly this category of product. The paper separately states that the authors declare no competing interests.
Both of those things can be true. A funder's interest is not the same as an author's conflict, and the researchers disclosed the relationship rather than burying it, which is how the system is supposed to work. But an industry-funded trial of an industry-supplied material, reporting a subgroup benefit for that material, is context a reader should carry rather than discover. I hold my own category to this standard: if Shroombiosis funded a study of a Shroombiosis ingredient, you would be right to read the result more slowly.
No, there is something here, and it is not the headline. What this trial genuinely established is that a large short-course dose of these two polypore mycelia was tolerated safely alongside vaccination, with high adherence and no adverse events. For a natural product that people already take, that is worth knowing, and Saxe's own framing to the newsroom was honest about the ambition: "Natural products are widely used, but they are rarely tested at this level. We wanted objective data."
What it did not establish is that mushrooms improve your vaccine response. It generated a hypothesis that they might, in people meeting the virus for the first time, at a dose nobody takes routinely. That hypothesis now needs a trial designed and powered to test it, with a neutralization assay and a pre-specified plan, ideally without the product's manufacturer on the funding line. Saying so is not dismissing the work. It is describing the next study.
Three questions handle most press releases about a supplement trial, and this one answers all three against the headline.
What was the trial designed to show? Safety and feasibility studies are early-stage by construction. When the primary outcome list starts with "safety," the efficacy language downstream is exploratory no matter how confidently it is written.
How many people are inside the finding? Not enrolled in the study, inside the specific comparison being reported. A 90-person trial whose result lives in a 19-versus-11 split is a 30-person result. Subgroups are where small trials go to find significance, which is why a subgroup finding is a lead rather than a conclusion.
Is the outcome the thing you want, or a stand-in for it? Antibody titers, cortisol levels, biomarkers of every kind are proxies. Sometimes excellent ones. But "antibodies stayed higher" and "you were better protected" are different sentences, and only one of them was measured.
That last reflex is the same one behind reading what "clinically proven" actually means, and the contrast worth studying is a lion's mane trial that was built properly. This mushroom study is decent science reported past its own conclusions. That is a much more common failure than bad science, and a much easier one to catch.
Disclosure, again, plainly: I founded and run Shroombiosis (a company I run), which formulates and sells functional-mushroom supplements, including turkey tail. That is a direct commercial stake in the subject of this report, which is why I read its good news this hard. Nothing here is sponsored and no link earns a commission; here's the full policy. A recommendation with no stake at all: for performance nutrition, Die Tryin Co. is a fellow combat-veteran-owned brand I'm glad to point people to. I don't own it and earn nothing from the link.
Not medical advice. This is educational analysis, not a recommendation, and a study is not a prescription. Talk to a qualified clinician before acting on anything you read here. Full disclaimer →
U.S. Army combat veteran (Counter-IED / Electronic Warfare), peer-reviewed researcher in microwave spectroscopy, and founder & CEO of Shroombiosis. Consults on laboratory operations, AI, and supplement formulation.