Mushrooms for the Immune System: What Reishi, Turkey Tail and Shiitake Have Actually Been Tested For

Reishi (Ganoderma lucidum, lingzhi), turkey tail (Trametes versicolor, yun zhi), shiitake (Lentinula edodes) and cordyceps are the four medicinal mushrooms most often sold “for the immune system” — and the honest summary of the research is this: their beta-glucans do measurably change immune-cell activity in people within four to twelve weeks, but almost no trial has asked whether that keeps a healthy person from getting sick. What exists is a handful of small, placebo-controlled studies that counted immune cells — 52 adults eating shiitake for 4 weeks, 79 men taking cordyceps for 4 weeks, healthy adults on a reishi beta-glucan for 84 days, 39 older women on a reishi extract for 8 weeks — plus a larger literature on colds that was mostly run with beta-glucan from baker’s yeast, not from mushrooms. Below is every one of those studies, with its size and duration next to every claim, and a plain statement of what no one has measured.

Which medicinal mushroom is best for the immune system?

If you choose by human trials in healthy people, shiitake and cordyceps have the cleanest placebo-controlled data — four weeks each, with immune-cell measures moving in the expected direction. If you choose by tradition and by the balance-rather-than-boost profile, reishi. If you choose by the sheer weight of clinical research, turkey tail — but that research is on an isolated pharmaceutical polysaccharide given alongside cancer treatment, not on a supplement taken by a healthy adult. That is the whole field, and it is smaller than the search results make it look.

The table lists every human study we could find in PubMed in which a reishi, turkey tail, shiitake or cordyceps preparation was tested against a control and an immune measure was recorded. The “what it does not mean” column is the one to read twice.

Two things stand out. First, the trials in healthy people are consistent in direction — immune cells respond within four to twelve weeks — but every one of them measured cells in a tube, not sick days in a diary. Second, the studies that did count infections used beta-glucan from yeast or oyster mushroom, at a purified dose that a tincture does not state. A 2021 systematic review of 34 randomised trials of fungal beta-glucans (from yeast, oyster mushroom, shiitake and reishi; 2.5–1,000 mg a day for up to 6.5 months) reached the same conclusion: fewer and milder respiratory infections, no adverse events attributable to the glucans, and “inconsistent” findings at the cellular level.

How do beta-glucans “train” the immune system?

Through a receptor, not through magic. Beta-1,3/1,6-glucans are long chains of glucose in the fungal cell wall that human cells do not make. Innate immune cells — macrophages, dendritic cells, neutrophils — carry a receptor called Dectin-1 whose original job is to recognise exactly that pattern, because it is what a fungus looks like. When Dectin-1 binds a beta-glucan, the cell becomes more alert, and there is now good evidence that the effect can persist: beta-glucans are one of the best-studied triggers of “trained immunity”, a form of long-term memory in innate immune cells that was thought not to exist until about a decade ago.

That is the whole reason a mushroom’s beta-glucan percentage is the number to look at, and why “total polysaccharides” on a label is not: the starch from a grain substrate is a polysaccharide too, and Dectin-1 does not recognise it. Our beta-glucan versus polysaccharides page goes through the chemistry, and the fruiting body versus mycelium page explains why a “mushroom” grown on rice can be mostly rice. Two caveats from the reviews are worth carrying with you: the human evidence for trained immunity is weaker than the animal and cell evidence, and “more alert” is not automatically “better” — which is the subject of the balance section below. The original explanation from this article is kept here; it was written before the trained-immunity literature and holds up well against it.

Does reishi support immune function in people?

In the two placebo-controlled trials that measured it, yes — and in a direction that is more interesting than “boost”. Over 84 days a purified reishi beta-glucan raised T-cell and NK-cell counts, IgA and NK killing activity in healthy adults. Over 8 weeks, 2,000 mg a day of reishi dry extract in older women made lymphocytes more responsive when challenged while shifting their gene activity toward the regulatory, anti-inflammatory side. A 10-day safety trial in 16 volunteers found no adverse effects and a non-significant rise in NK cells. None of these trials counted infections.

The wider reishi literature is large but mostly medical. A Cochrane review of reishi in cancer care found five randomised trials and called their quality “unsatisfying”; a 2025 GRADE-assessed meta-analysis of 17 randomised trials in 971 people — healthy, at-risk and chronically ill — found modest effects on a few metabolic markers, no significant effect on inflammatory markers, and rated the certainty of evidence “very low” across the board. That is not a reason to dismiss reishi; it is a reason to describe it accurately. What the human data supports is a regulator that nudges the immune response toward balance over weeks, which is exactly how the tradition describes it and why we put reishi, not a stimulant, into the immune blend. The full reishi story — compounds, trials, product-quality problems — is on the complete reishi guide; the original reishi section of this article is kept below.

What has turkey tail actually been tested for?

Mostly for something you are not buying it for. The famous turkey tail evidence is PSK (polysaccharide-K, “Krestin”), a protein-bound polysaccharide extracted from the mushroom and used in Japan as a prescription adjunct to cancer treatment since the 1970s: a meta-analysis of 8 randomised trials in 8,009 patients after gastric-cancer surgery found a survival hazard ratio of 0.88, and a 2023 systematic review of 39 clinical mushroom studies confirmed a survival benefit for PSK in four gastric-cancer trials. For a healthy adult taking a turkey tail extract, the relevant human data is one phase-1 study in 9 women — well tolerated up to 9 g a day for 6 weeks, with “trends” toward more lymphocytes and NK activity, and no placebo group.

We say this plainly because “turkey tail: over 400 clinical trials” is the most-copied sentence on the pages competing with this one, and it is doing quiet work: the trials are real, but they are of PSK and its Chinese cousin PSP, at pharmaceutical doses, in patients. What carries over to a fruiting-body extract is the class of molecule — turkey tail is unusually rich in beta-glucans and protein-bound polysaccharides — and the safety record. What does not carry over is the outcome. This is also why our lab result for the immune blend is a beta-glucan percentage on the finished extract and not a claim about what it does: the turkey tail science page covers PSK and PSP in more detail, and the lab-testing page shows the report. One more honesty point: our pure turkey tail extract has not been sent for its own beta-glucan test — only the turkey tail and reishi blend has — so the 23.21% figure on this page belongs to the blend and to nothing else.

Does shiitake improve immunity?

In the one modern trial that asked, eating it did: 52 healthy adults who ate 5 or 10 g of whole dried shiitake every day for 4 weeks showed 60% more proliferation of γδ-T cells and twice as much of NK-T cells when their blood was tested, higher salivary IgA (the gut’s front-line antibody), lower C-reactive protein, and a cytokine pattern the authors describe as “less inflammatory” than before. It is the cleanest demonstration in the field that a mushroom, as food, moves human immune markers — and it was done with the whole mushroom, not lentinan.

Lentinan, the isolated beta-glucan the original article describes below, has a separate and older clinical history as an injected adjunct in Japan; a 2021 systematic review of fungal beta-glucans given alongside cancer treatment (16 trials, 1,650 patients) found it and its relatives safe and well tolerated, with mixed evidence on whether they blunt treatment-related immune suppression. As with PSK, that is drug research and should be read as such. We do not sell shiitake — it is a culinary mushroom and is easy to buy fresh — and the Dai trial is a good argument for simply eating it. The original shiitake section is kept here:

What about cordyceps and the immune system?

Cordyceps has two of the better-designed trials in healthy people. In 79 healthy men, 4 weeks of 1.5 g a day raised NK-cell activity, lymphocyte proliferation and the Th1 cytokines IL-2 and interferon-γ more than placebo, with no adverse reactions. In 79 healthy adults, 8 weeks of 1.68 g a day of a cordyceps mycelium culture extract raised NK-cell cytotoxicity by 38.8% relative to placebo. Both are cell-marker studies; neither counted infections. Cordyceps polysaccharides are also the subject of a 2024 review of twenty years of laboratory and animal work showing activation of macrophages, lymphocytes and dendritic cells.

In practice we position cordyceps as the energy mushroom rather than the immune mushroom — that story, with its own trial table, is on cordyceps and energy — but the immune data is the reason it belongs in a morning routine during a hard season of training or work. The original section is kept below; note that it originally named the cordyceps species, which we no longer state on any page, for reasons explained on the cordyceps science page.

Do mushroom beta-glucans mean fewer colds?

Probably fewer or milder ones, but the strongest trials were not run with mushrooms. In 162 adults with recurring colds, 16 weeks of 900 mg a day of baker’s-yeast beta-1,3/1,6-glucan cut symptomatic colds by 25% versus placebo; in 299 adults the same dose did not change the number of colds but made the first week of each one milder. The mushroom-derived data is smaller: 50 athletes on an oyster-mushroom beta-glucan for 3 months had fewer infection symptoms and more NK cells, and an 11–18-week trial of maitake in 2026 found no change in the number of infections but fewer days of fever and runny nose with one of two strains.

The fair reading is that the molecule works in the direction claimed, that dose and form matter, and that no trial has tested a mushroom tincture against a winter of colds. We cannot tell you how many milligrams of beta-glucan are in a millilitre of our extract — the lab measures the percentage in the dried extract, and turning that into a per-drop figure would require an extraction-yield number we have not verified, so we do not publish one. What we can tell you is that the percentage is measured, and that it is the highest-value marker the reviews point to. The original “why the immune system needs support” opening of this article is kept in the last section of the page.

Is “boosting” the immune system even the right goal?

Usually not, and the trials quietly agree. The reishi extract trial in older women is the clearest example: the extract made lymphocytes more responsive and shifted them toward the regulatory, anti-inflammatory side — fewer Th17 cells, more IL-10 — which is why the authors chose the word “regulates”. The shiitake trial found immune cells more active under conditions that were, in the authors’ words, “less inflammatory than those that existed before”. An immune system that is simply louder is not healthier; allergies and autoimmune conditions are immune systems that are too loud.

This is the practical reason the language on this page is “support” and “balance” rather than “boost”, and it is also a safety point. If you have an autoimmune condition, take an immunosuppressant, or have had an organ transplant, a substance that makes immune cells more responsive is precisely what your physician needs to know about before you start. The drug-interactions page lists what is documented; the reishi and seasonal allergies page covers the “too loud” side of the system separately. The original discussion of balance from this article is kept below.

How long does immune support take to show?

Four weeks is the shortest interval in which a placebo-controlled trial found a change in immune cells (shiitake, cordyceps); the reishi trials ran 8 weeks and 84 days; the cold-prevention trials ran 12 to 16 weeks, across a winter. The 10-day reishi trial found nothing significant. So the honest window is one to three months of daily use — and if what you want to know is whether you get fewer colds, a single winter is the only fair test, because colds are seasonal and a good month proves nothing.

We have written the whole “how long” question up on its own page — how long medicinal mushrooms take to work — including a simple way to run a one-person trial so that you are not fooled by chance. For immunity the version is: note every cold, its length and its severity for the season before you start, and compare next season. Memory is a poor diary; a phone note is a good one. One 50 ml bottle at 1.4 ml a day is about 35 days, which covers the four-week window the shortest trials used.

How much, and in which form?

The trial doses are not tincture doses, and we will not pretend they convert. The people studies used 5–10 g of whole dried shiitake, 1.5–1.68 g of cordyceps powders or mycelium extract, 2,000 mg of reishi dry extract, 3–9 g of a turkey tail preparation, and 250–900 mg of purified beta-glucan. Our label dose is 1.4 ml a day, and our dosage guide explains the four-week titration we use and why we do not publish a milligram-per-millilitre figure.

What we can state exactly is what is in the bottle: a triple extraction (water, alcohol and ultrasonic) of fresh turkey tail and reishi fruiting bodies at a mushroom-to-liquid ratio of 1:3 — about 16–17 g of fresh mushroom in every 50 ml — with beta-glucan measured at 23.21% of the dry extract by TÜV Austria and the report published. The mushrooms go from harvest to extraction without a drying step, which, as far as we know, makes us one of very few growers in the world to do so; the fresh versus dried page explains what that does and does not change. The extraction-ratio page explains why “1:3” on a fresh-mushroom label is not the same 1:3 as on a dried-mushroom label, and the timing and stacking guide covers when to take it and what to combine it with.

Who should not take medicinal mushrooms for immune support?

Anyone on an immunosuppressant or biologic, anyone with an autoimmune condition or an organ transplant, anyone on blood thinners (reishi has documented anti-platelet activity), anyone due for surgery within two weeks, and — by our own rule rather than by evidence of harm — anyone pregnant, breastfeeding or under 18. Those are physician conversations, not supplement decisions. Mushroom allergy exists and is a reason to stop at the first sign of a reaction.

We keep this section on a sales page on purpose. The side-effects page lists what has been reported in the trials (mostly mild digestive complaints), the drug-interactions page covers anticoagulants and immunosuppressants in detail, the pregnancy and breastfeeding page explains why our answer there is no, and the children’s page does the same for anyone under 18. The original safety questions from this article are preserved in the FAQ section below.

What makes an immune extract worth testing?

Three things you can check before you buy. That it is made from fruiting bodies, not mycelium grown on grain — a grain-grown “mushroom” is mostly starch, which Dectin-1 ignores. That the beta-glucan content is measured by an external laboratory on the finished extract and the report is open, with alpha-glucan (starch) reported as not detected. And that the label does not hide behind “total polysaccharides”. A 2017 analysis of 19 reishi products sold in the United States found that only 5 contained what their labels claimed; the immune category is where that problem is worst, because turkey tail and reishi are cheap to grow as mycelium on rice.

Our own answers to those three checks are on the lab-testing page and the how to read a COA guide; the mycelium debate page explains, without name-calling, why the biggest brands in this category disagree with us. The original buying advice from this article is kept here — it still holds:

What does the research still not know?

Whether a healthy adult taking a mushroom extract gets fewer or shorter infections — no trial has tested a tincture against a winter. Whether the immune-cell changes seen at four to twelve weeks persist, fade or matter clinically. Which form (whole mushroom, water extract, alcohol extract, purified beta-glucan) does what, and at which dose in drops. Whether the “regulating” profile of reishi and the “activating” profile of cordyceps and shiitake add up or cancel when combined. We do not know these things, and neither does anyone selling an immune blend.

What we can measure, we do: the extract’s beta-glucan content, its heavy-metal, pesticide and PAH results, and the ratio of fresh mushroom to liquid. “Studies show” is not something we can put on a certificate. A lab result is — which is why the proof panel below this article shows numbers with a report number, and not a sentence about NK cells in a dish.

The bottom line

Medicinal mushrooms are the best-supported natural source of beta-glucans, and beta-glucans do change human immune-cell activity within four to twelve weeks — that part is measured, in shiitake, cordyceps and reishi trials. What is not measured is whether that keeps you well; the “fewer colds” trials mostly used yeast beta-glucan, and turkey tail’s famous evidence is a prescription polysaccharide in cancer care. Choose a fruiting-body extract with an open beta-glucan report, take it daily for at least a month, judge it over a season rather than a week, and talk to a physician first if your immune system is medically suppressed or medically overactive. The original closing of this article is kept below.

Frequently asked questions about mushrooms and the immune system

How this article began (the original 2025 opening, kept)

This page was first published as an educational overview and rebuilt in August 2026 around the trial evidence above. Nothing was thrown away: every section of the original sits in a grey box under the question it answers, and the opening — written before we had read a single one of these studies closely — is here. It is a fair record of how the conversation about mushrooms and immunity usually starts.

Sources (peer-reviewed)

1. Whole shiitake, 5–10 g a day for 4 weeks in 52 healthy adults — γδ-T proliferation +60%, NK-T twofold, higher IgA, lower CRP. Dai X, Stanilka JM, Rowe CA, et al. Journal of the American College of Nutrition, 2015. View on PubMed
2. Cordyceps 1.5 g a day for 4 weeks in 79 healthy men — higher NK activity, lymphocyte proliferation, IL-2 and IFN-γ than placebo. Kang HJ, Baik HW, Kim SJ, et al. Journal of Medicinal Food, 2015. View on PubMed
3. Cordyceps mycelium culture extract, 8 weeks in 79 healthy adults — NK cytotoxicity +38.8% relative to placebo. Jung SJ, Jung ES, Choi EK, et al. BMC Complementary and Alternative Medicine, 2019. View on PubMed
4. Reishi beta-1,3/1,6-glucan for 84 days in healthy adults — higher T-cell and NK counts, IgA and NK cytotoxicity than placebo. Chen SN, Nan FH, Liu MW, et al. Foods, 2023. View on PubMed
5. Reishi dry extract 2,000 mg a day for 8 weeks in older women — T lymphocytes shifted toward a regulatory, anti-inflammatory profile. Iser-Bem PN, Lobato TB, Alecrim-Zeza AL, et al. British Journal of Nutrition, 2024. View on PubMed
6. Reishi extract 2 g twice daily for 10 days in 16 volunteers — safe; NK-cell rise not significant. Wicks SM, Tong R, Wang CZ, et al. American Journal of Chinese Medicine, 2007. View on PubMed
7. Reishi in cancer care — Cochrane review of 5 randomised trials; quality “unsatisfying”. Jin X, Ruiz Beguerie J, Sze DM, Chan GC. Cochrane Database of Systematic Reviews, 2016. View on PubMed
8. Reishi in clinical trials — GRADE-assessed meta-analysis of 17 RCTs, 971 participants; very low certainty; no effect on inflammatory markers. Jafari A, Mardani H, Mirzaei Fashtali Z, Arghavan B. Food Science & Nutrition, 2025. View on PubMed
9. Turkey tail preparation up to 9 g a day for 6 weeks after radiotherapy — phase 1, 9 women, safe, immune “trends”. Torkelson CJ, Sweet E, Martzen MR, et al. ISRN Oncology, 2012. View on PubMed
10. PSK (turkey tail polysaccharide) as adjuvant after gastric-cancer surgery — meta-analysis of 8 RCTs, 8,009 patients, hazard ratio 0.88. Oba K, Teramukai S, Kobayashi M, et al. Cancer Immunology, Immunotherapy, 2007. View on PubMed
11. Medicinal mushroom supplements in cancer — systematic review of 39 clinical studies, 2010–2020. Narayanan S, de Mores AR, Cohen L, et al. Current Oncology Reports, 2023. View on PubMed
12. Fungal beta-glucans given alongside cancer treatment — systematic review of 16 trials, 1,650 patients. Steimbach L, Borgmann AV, Gomar GG, et al. Clinical Nutrition, 2021. View on PubMed
13. Fungal beta-1,3/1,6-glucans and health — systematic review of 34 randomised trials. Vlassopoulou M, Yannakoulia M, Pletsa V, et al. Food & Function, 2021. View on PubMed
14. Oyster-mushroom beta-glucan (pleuran) for 3 months in 50 athletes — fewer respiratory-infection symptoms, more NK cells. Bergendiova K, Tibenska E, Majtan J. European Journal of Applied Physiology, 2011. View on PubMed
15. Yeast beta-1,3/1,6-glucan 900 mg a day for 16 weeks in 162 adults — 25% fewer symptomatic colds. Auinger A, Riede L, Bothe G, et al. European Journal of Nutrition, 2013. View on PubMed
16. Yeast beta-glucan 900 mg a day for 16 weeks in 299 adults — milder first-week cold symptoms; incidence unchanged. Dharsono T, Rudnicka K, Wilhelm M, Alexander C. Journal of the American College of Nutrition, 2019. View on PubMed
17. Maitake for 11–18 weeks in healthy adults — fewer fever and runny-nose days with one strain; infection count unchanged. Masuda Y, Nakayama Y, Shimizu R, et al. Food & Function, 2026. View on PubMed
18. Dectin-1, beta-glucans and trained immunity — review. Mata-Martínez P, Bergón-Gutiérrez M, Del Fresno C. Frontiers in Immunology, 2022. View on PubMed
19. Beta-1,3/1,6-glucans and immunity — state of the art; human evidence weaker than pre-clinical. De Marco Castro E, Calder PC, Roche HM. Molecular Nutrition & Food Research, 2021. View on PubMed
20. Shiitake polysaccharides and immune modulation — review of animal and human work. Roszczyk A, Turło J, Zagożdżon R, Kaleta B. International Journal of Molecular Sciences, 2022. View on PubMed
21. Genomic analysis of 19 commercial reishi products — only 5 matched their labels. Wu DT, Deng Y, Chen LX, et al. Scientific Reports, 2017. View on PubMed

Further reading on this site: Reishi science · Turkey tail science · Cordyceps science · the research hub, filtered for immunity · turkey tail for immunity — our extract page · the complete guide to medicinal mushrooms · all solutions by goal · mushrooms for sleep · mushrooms for focus.

*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.* This page is an educational overview of published research and does not constitute medical advice. Medicinal mushroom extracts are dietary supplements. Do not begin use while taking medication, during pregnancy or nursing, or with an existing medical condition, without consulting a physician.