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What Is Agaricus blazei? The Royal Sun Mushroom Explained

Agaricus blazei is credited with four RCTs for immune support and cancer care. Two tested multi-ingredient products, one missed its primary endpoint, and the safety file includes two deaths. Here's the actual record.

RethinkMushrooms Research TeamUpdated 32 min read

Agaricus blazei (Royal Sun Mushroom)

2 of 4 widely cited 'Agaricus blazei trials' tested a multi-ingredient product, not the mushroom on its own

Agaricus blazei is routinely described as having four randomized controlled trials behind it. Two of those four gave patients a blended product — one an 82% ABM mushroom mix, one a multivitamin and mineral complex — so their results cannot be attributed to the mushroom alone.

Tangen J-M et al., BioMed Research International, 2015; Kim et al., 2025

p = 0.04

the one clean placebo-controlled result for Agaricus blazei alone: lower insulin resistance in 60 type 2 diabetes patients (Hsu 2007)

2 deaths

from fulminant hepatitis in a three-patient case series of Agaricus blazei users, with one positive rechallenge (Mukai 2006)

3 names

same mushroom: A. blazei, A. subrufescens, A. brasiliensis. One species, taxonomic confusion resolved (Kerrigan 2005)

Tangen J-M et al., BioMed Research International, 2015; Kim et al., 2025

Illustration of Agaricus blazei Royal Sun Mushroom with its distinctive golden cap alongside immune system activation diagramView as image ↗

Most Western supplement consumers have never heard of Agaricus blazei. In Japan, the story is different. Agaricus blazei became a popular dietary supplement there from 1991 onward, and within its first ten years the number of Japanese consumers had grown into the hundreds of thousands, supported by roughly 15 to 20 tons of product annually across some 20 manufacturers.[10]

That popularity produced a genuine clinical literature, and it is more substantial than most English-language supplement pages acknowledge. It also produced something the enthusiastic write-ups tend to leave out: a safety file, a product recall, and a set of published liver injuries.

The honest version of the Agaricus blazei story is neither "no good evidence" nor "four RCTs prove it works." It is a mushroom with one clean placebo-controlled human result, several trials that tested something other than the mushroom by itself, a mechanism literature whose most confident reviews come from authors with a commercial stake, and a small but serious record of hepatic harm.

This article covers what Agaricus blazei is, where it actually came from, what its chemistry does and does not establish, what each human trial genuinely measured, and where the safety questions stand.

Key Takeaways

  • Agaricus blazei Murill (also called Royal Sun Mushroom and Himematsutake) is best known as a Brazilian mushroom cultivated and studied in Japan, but the species was already being cultivated in eastern North America in the late 1800s before fading from commerce. Its correct taxonomic name is Agaricus subrufescens (Kerrigan 2005).
  • Four human trials are routinely counted as "Agaricus blazei RCTs," but two of them tested multi-ingredient products: Tangen 2015 used AndoSan (82% ABM plus two other mushrooms) and Kim 2025 used a multivitamin and mineral complex containing ABM. Neither can attribute its findings to Agaricus blazei alone.
  • The cleanest result is Hsu 2007: a randomized, double-blind, placebo-controlled trial in which ABM extract lowered HOMA-IR insulin resistance (3.6 vs 6.6, p = 0.04) in 60 analyzed type 2 diabetes patients over 12 weeks.
  • Two trials did not deliver what they are usually cited for. Tangen 2015 found no significant difference in treatment response, overall survival, or time to new treatment. Kim 2025 missed its primary endpoint (NK activity recovery 17.8% vs 9.9%, p = 0.104).
  • The popular claim that ABM beta-glucans uniquely trigger dectin-1, CR3, and TLR2 simultaneously is not supported. The paper usually cited for TLR2 (Kasai 2004) explicitly found its effect was NOT blocked by anti-TLR2 antibody, and no head-to-head study has compared receptor engagement across mushroom species.
  • The mechanism review most often cited for ABM's Th1/Th2 story (Hetland 2011), the three-mushroom comparative review (Hetland 2020), and the myeloma RCT (Tangen 2015) share an author who is a cofounder and shareholder of the company distributing the extract under evaluation. Each paper discloses this; citations of them rarely do.
  • Agaricus blazei has a real safety file. Mukai 2006 reported three advanced cancer patients with severe hepatic damage, two of whom died of fulminant hepatitis; Hisamochi 2013 added two RUCAM-confirmed liver injury cases resembling autoimmune hepatitis. In 2006 one Japanese ABM product tested Ames-positive and was withdrawn from the market.

What Agaricus blazei Is: One Mushroom, Three Names

Agaricus blazei Murill, the Royal Sun Mushroom, and Himematsutake are three names for the same species of edible medicinal fungus. The taxonomic history of this mushroom is worth understanding before reading the research on it, because papers from different decades and different countries use different names, and some readers comparing research across literature may not realize they're reading about the same organism.

The definitive taxonomic authority is Kerrigan's 2005 paper in Mycologia.[6] Working from DNA sequence analysis of the rDNA ITS region, mating studies, and genetic analysis of hybrid progeny, Kerrigan made what the paper calls "a strong case for conspecificity of the Brazilian mushrooms with A. subrufescens," and accepted the recent lectotypification of that name. Agaricus blazei Murill (sensu Heinemann), Agaricus brasiliensis, and Agaricus rufotegulis are all treated as the same species. Most scientific literature predating that revision used "A. blazei," and many current papers still use it because it remains more recognizable. This article uses "Agaricus blazei" and "ABM" because that's what most readers searching for the mushroom will encounter.

"Royal Sun Mushroom" is the English marketing name, most prominently used by Wang and colleagues' 2013 review in Evidence-Based Complementary and Alternative Medicine, which catalogued the full scope of documented health effects.[7] "Himematsutake" is the Japanese trade name for the cultivated strain, meaning "Princess Matsutake," a name that compares it favorably to matsutake (Tricholoma matsutake), Japan's most prized culinary mushroom.

The species is a medium-sized agaric with a distinctive almond-like or anise scent — the reason it is also called the "almond mushroom."[20] Caps are golden-brown, roughly 5–11 cm in diameter. The gills are white when young, turning pink and then dark brown as spores mature, and the spore print is chocolate-brown. It bruises reddish-brown when damaged. Its natural habitat is woodland edges and grass in tropical and subtropical South America, particularly Brazil, though as noted below the species also has a documented history in North America and Europe.

Where It Actually Came From: A Longer History Than the Marketing Suggests

The origin story attached to Agaricus blazei supplements is a good one: a Japanese-Brazilian farmer near Piedade, in the mountains of São Paulo state, notices the locals eating an abundant wild mushroom and enjoying unusually low rates of cancer, and ships samples to researchers in Japan. Versions of this narrative appear on nearly every retailer page selling the mushroom.

It is worth knowing that this account circulates almost entirely in commercial and popular sources rather than in the peer-reviewed record, and that the peer-reviewed record tells a longer and less romantic story. The species was described in 1893 and, as Kerrigan documents, Agaricus subrufescens "was cultivated first in the late 1800s in eastern North America," where it was "once a popular market mushroom" before it "faded from commerce in the early 20th century."[6][20] The Brazilian mushroom that later reached Japan was a reintroduction of a species Western growers had already cultivated and forgotten, not a wholly new discovery.

What is well documented is what happened next. Agaricus blazei became a popular dietary supplement in Japan from 1991, and Ohno and colleagues record that "for the first 10 years, Agaricus blazei Murill consumers had grown to several hundreds of thousands with no reports of any serious side effects."[10] At the time of their study there were at least 20 manufacturers and roughly 100 Agaricus-derived supplement products on the Japanese market, with annual consumption of about 15 to 20 tons. The cultivated Japanese strain was branded "Himematsutake."

That market scale is the reason a mushroom essentially unknown in the West has any clinical literature at all — and, as the safety section below describes, it is also the reason Japanese regulators eventually took an interest. Firenzuoli and colleagues' 2008 review in Evidence-Based Complementary and Alternative Medicine surveyed both halves of that story.[1]

What Makes ABM Chemically Distinctive

Agaricus blazei's pharmacological properties stem from a complex bioactive chemistry that has been extensively characterized. Da Silva de Souza and colleagues' 2017 review in Current Pharmaceutical Design catalogued the full range of bioactive classes, describing ABM as one of the chemically best-characterized medicinal mushrooms.[3]

Beta-1,3-/1,6-glucans: The primary and most studied bioactives, and the source of the single most-repeated claim about this mushroom — that ABM's beta-glucans uniquely engage dectin-1, complement receptor 3 (CR3), and Toll-like receptor 2 (TLR2) all at once, in a combination no other mushroom matches.

That claim does not survive contact with the papers it cites. The study most often invoked as the TLR2 evidence, Kasai and colleagues' 2004 work on ABM fraction H in human peripheral mononuclear cells, reports the opposite: IL-12 production "was inhibited by anti-CD14 and anti-TLR4 antibodies but not by anti-TLR2 antibody."[17] It is a CD14/TLR4 paper. A separate study, Liu 2015, did conclude that an ABM polysaccharide acts through TLR2, on the evidence that it "did not inhibit tumour growth in TLR2(-/-) mice" — but that used a different preparation, a different model, and a different readout.[18] Dectin-1 and CR3, meanwhile, are the two best-characterized beta-glucan receptors across fungal immunology generally; nothing establishes them as distinctive to this species.[19]

Four receptors, two disagreeing studies

The “Triple Receptor” Claim vs. the Primary Literature

The marketing claim is CR3 + dectin-1 + TLR2, fired simultaneously and uniquely. What the source papers show is two general fungal receptors, plus two Toll-like receptors identified by studies that used different preparations and reached opposite conclusions.

Dectin-1

C-type lectin receptor

General biology

Recognizes the 1,3-glucan structure common to fungal cell walls; the standard beta-glucan pathway.

Source: Reviewed by Hetland 2008

Not ABM-specific

CR3

Complement receptor 3 (CD11b/CD18)

General biology

One of the two best-characterized beta-glucan receptors across fungal immunology.

Source: Reviewed by Hetland 2008

Not ABM-specific

TLR4 + CD14

Toll-like receptor 4

Directly tested

IL-12 induction blocked by anti-CD14 and anti-TLR4 antibodies — and explicitly NOT blocked by anti-TLR2.

Source: Kasai 2004, human PBMC

Mycelial fraction H

TLR2

Toll-like receptor 2

Directly tested

MDSC M2→M1 reprogramming; anti-tumor effect absent entirely in TLR2-knockout mice.

Source: Liu 2015, mouse tumor model

Polysaccharide fraction

Both Toll-like receptor findings can be true — different preparations, cells, and readouts — which is consistent with Hetland 2008’s report of “highly different biological potency between AbM extracts of different source and manufacturing.” What it does not support is a single proven triple-receptor signature unique to this species. No head-to-head study has compared receptor engagement across mushroom species.

Sources: Kasai et al., 2004 (RTHM-00134, PMID 15841259); Liu et al., 2015 (RTHM-00722, PMID 26194418); Hetland et al., 2008 (RTHM-00251, PMID 18782264).

Both Toll-like receptor findings can be true at once, because they tested different things — which is consistent with Hetland's 2008 observation of "highly different biological potency between AbM extracts of different source and manufacturing."[19] What the literature does not contain is a demonstrated triple-receptor signature unique to Agaricus blazei, or any head-to-head study comparing receptor engagement across mushroom species. Claims that ABM produces "consistently stronger immune activation than other medicinal mushrooms" have no such comparison behind them.

Proteoglycans: Protein-polysaccharide complexes distinct from pure polysaccharides; contribute to immune modulation through pathways separate from the beta-glucan receptors.

Blazein and Blazeispirol: Steroidal compounds unique to ABM with documented anti-tumor and anti-inflammatory activities in preclinical research. Huang and colleagues' 2022 comprehensive chemical composition review confirmed that Blazein has been shown to induce apoptosis in cancer cell lines in multiple studies.[5]

Ergosterol: The provitamin D2 compound present in all fungi. Standard in the Agaricus family.

Agaritine: A hydrazine derivative present in Agaricus species including A. blazei. Firenzuoli and colleagues describe it flatly as "a well-known carcinogenic and toxic substance in animals, that must be completely and fully evaluated."[1] This is a live safety question, discussed further below and in The Agaritine Controversy: Carcinogen or Harmless?.

Phenolic acids and terpenes: Antioxidant compounds present in moderate amounts; contribute to the hepatoprotective effects documented in some studies.

Huang 2022 confirmed that the chemical complexity of ABM is directly responsible for its multi-target effects: different compound classes operate through different mechanisms, collectively accounting for the immune, anti-cancer, anti-diabetic, and hepatoprotective effects documented across preclinical and clinical research.[5]

The Proposed Mechanism Behind Four Health Effects: Th1/Th2 Balance

One of the more elegant findings in ABM research is that seemingly unrelated health benefits (tumor suppression, infection resistance, reduced allergic reactions, and reduced inflammation) can be explained by a single underlying mechanism.

Hetland and colleagues articulated this clearly in their 2011 systematic review.[2] The human immune system has two broad response modes, typically described as Th1 (cell-mediated immunity, directed at viruses, bacteria, and tumor cells) and Th2 (humoral immunity, associated with antibody responses, allergies, and parasite defense). In many disease conditions, this balance is disrupted.

In allergic conditions, Th2 responses are excessive. In some cancer types and chronic infections, Th1 responses are suppressed. In autoimmune inflammation, both systems may be dysregulated.

ABM's beta-glucans modulate the innate immune system in a way that tends to shift the balance toward Th1 where Th2 is dominant (helping with allergy and certain cancer contexts), while also reducing excessive inflammatory signaling in Th1-excess conditions. This dual regulatory action is what makes a single mushroom extract appear effective across such a wide range of conditions.

The 2011 review described this as "amelioration of Th1/Th2 imbalance" operating through innate immunity modulation, specifically the activation of monocytes, dendritic cells, NK cells, and granulocytes.[2]

One thing to carry into the rest of this article: this Th1/Th2 framing is largely the work of a single research group. Hetland's 2011 review, the 2020 comparative review, and the multiple myeloma trial discussed below share an author who discloses being an option and stock holder — and later a cofounder and shareholder — of ImmunoPharma AS, the Norwegian company that distributes the AndoSan ABM extract those papers evaluate.[2][11][4] The disclosures are properly made in each paper. They are almost never repeated by the pages that cite them.

Who paid, who benefits, who is independent

The Disclosure Line Under the Agaricus blazei Evidence Base

Three of the most-cited Agaricus blazei papers — the mechanism review, the comparative review, and the transplant RCT — share an author who co-founded and holds stock in the company distributing the extract under evaluation. Each paper discloses this. Almost nothing that cites them repeats it.

Tied to the extract’s distributor

Hetland 2011

Commercial tie disclosed

The Th1/Th2 mechanism review this article is built on

"G. Hetland and E. Johnson are option and stock holders in ImmunoPharma AS."

Tangen 2015

Commercial tie disclosed

The multiple myeloma transplant RCT

"AndoSan was provided free by Immunopharma AS… which also provided a research grant." "Geir Hetland is a cofounder and shareholder of Immunopharma AS."

Hetland 2020

Commercial tie disclosed

The three-mushroom comparative review

"Geir Hetland is a cofounder and shareholder of Immunopharma, Oslo, Norway." Immunopharma provided AndoSan free of charge.

Independent of it

Ahn 2004

Independent

Gynaecological cancer NK activity and quality of life

Tested ABMK, a Kyowa product. No Immunopharma involvement.

Hsu 2007

Independent

The type 2 diabetes RCT — the cleanest ABM-only trial

Independent academic trial in registered diabetes patients.

Ohno 2011

Independent

The Phase I safety study

Grant-in-Aid for Cancer Research, Japanese Ministry of Health, Labor and Welfare.

Mukai 2006 · Hisamochi 2013

Independent

The published hepatic injury cases

Independent clinical case reports. No commercial sponsor.

A disclosed interest is not misconduct, and these authors disclosed theirs properly. But it changes how much independent weight the record carries: the strongest positive framing of Agaricus blazei traces substantially to one research group with a stake in the product, while the trial with the cleanest independent design tested a surrogate endpoint in diabetes, and the independent clinical literature includes reports of serious harm.

Disclosures quoted from: Hetland et al., 2011 (RTHM-00399, PMID 21912538); Tangen et al., 2015 (RTHM-00738, PMID 25664323); Hetland et al., 2020 (RTHM-01201, PMID 32397163); funding statements from Ohno et al., 2011 (RTHM-00427, PMID 21584278).

The clinical implications run across multiple organ systems, which is why ABM research spans such a wide range of conditions. Each cluster article below covers one domain in depth. This pillar article covers the mechanism that connects them.

For the specific receptor-level mechanism and its application to anti-tumor immunity, see How Agaricus blazei Activates Anti-Tumor Immunity.

For the allergy and Th1/Th2 rebalancing story in depth, see How Agaricus blazei Shifts the Immune Response from Allergic to Protective.

The Clinical Evidence: What the Four Human Trials Actually Tested

"Four randomized controlled trials of Agaricus blazei" is the sentence that does most of the work in this mushroom's reputation. It is worth slowing down on, because the count is doing something the individual trials do not support. Two of the four tested a product that was not Agaricus blazei by itself. One does not describe a randomization procedure. One missed its own primary endpoint.

Four trials, two preparations, one met primary endpoint

What the “Four RCTs” Actually Tested

“Four randomised controlled trials of Agaricus blazei” is the sentence you will read everywhere. Two of the four gave patients a multi-ingredient product, so nothing they found can be attributed to the mushroom alone. One reports no randomisation procedure. One missed its own primary endpoint. Read the rows, not the headline count.

Ahn 2004

Isolates ABM

Swallowed: ABMK granulate — Agaricus blazei only

Measured: NK cell activity in gynaecological cancer patients on chemotherapy

Found: Significantly higher NK activity (P < 0.002); appetite, alopecia, emotional stability and general weakness improved

Did not show: No difference in lymphokine-activated killer activity, monocyte activity, or immune cell counts.

No randomisation or blinding described; arms uneven (39 vs 61)

Hsu 2007

Isolates ABM

Swallowed: ABM extract 1500 mg/day — Agaricus blazei only

Measured: HOMA-IR (insulin resistance) added to gliclazide + metformin

Found: Primary endpoint met: HOMA-IR 3.6 vs 6.6, p = 0.04; adiponectin +20% vs −12%, p < 0.001

Did not show: 60 patients analysed, single centre, 12 weeks. No clinical outcome measured — HOMA-IR is a surrogate.

Randomised, double-blind, placebo-controlled; 12 weeks

Tangen 2015

Multi-mushroom

Swallowed: AndoSan — 82% ABM, plus H. erinaceus and G. frondosa

Measured: Immune cell subsets and cytokines during stem cell transplant

Found: Increased Treg and plasmacytoid dendritic cells; increased IL-1ra, IL-5, IL-7

Did not show: No statistically significant difference in treatment response, overall survival, or time to new treatment.

Randomised, double-blind, placebo-controlled; n = 40, 33 evaluable

Kim 2025

Cannot isolate ABM

Swallowed: Multivitamin AND mineral complex containing ABM

Measured: NK cell activity recovery 30 days after NSCLC resection

Found: Primary endpoint missed: 17.8% vs 9.9%, p = 0.104. T cells p = 0.026, B cells p = 0.001

Did not show: No difference in cytokines, BMI, performance status, or patient-reported outcomes. Effects cannot be attributed to Agaricus blazei.

Randomised, double-blind, placebo-controlled multicentre pilot; n = 66

Strip out the multi-ingredient products and the trial that reports no randomisation, and the cleanest placebo-controlled evidence that Agaricus blazei alone changes a measured human outcome is a single 60-patient, 12-week diabetes trial with a surrogate endpoint. That is a real finding. It is not a treatment.

Sources: Ahn et al., 2004 (RTHM-00127, PMID 15304151); Hsu et al., 2007 (RTHM-00216, PMID 17309383); Tangen et al., 2015 (RTHM-00738, PMID 25664323, NCT00970021); Kim et al., 2025 (RTHM-02106, PMID 41595590).

Ahn 2004: Gynecological cancer patients (NK cells and quality of life)

Ahn and colleagues gave Agaricus blazei Murill Kyowa (ABMK) to gynecological cancer patients undergoing carboplatin-based chemotherapy.[8] Across 100 cervical, ovarian, and endometrial cancer patients, natural killer cell activity was significantly higher in the ABMK arm (ANOVA, n = 39, P < 0.002) than in the comparison arm (n = 61), and chemotherapy side effects including appetite, alopecia, emotional stability, and general weakness were reported as improved.

Two caveats matter and are usually dropped. The paper reports "no significant difference in lymphokine-activated killer and monocyte activities," nor in immune cell counts — so the immune effect was specific to NK activity rather than broad. And although this trial is universally described as randomized, the abstract describes no randomization or blinding procedure, and the arms are markedly uneven at 39 versus 61.

Hsu 2007: Type 2 diabetes (insulin resistance)

This is the strongest clean evidence Agaricus blazei has. Hsu and colleagues ran a genuine randomized, double-blind, placebo-controlled trial: 72 patients enrolled from a registry of 536, 60 analyzed, receiving 1500 mg/day of ABM extract or cellulose placebo for 12 weeks on top of existing gliclazide and metformin.[9] The ABM group finished with significantly lower insulin resistance (HOMA-IR 3.6 vs 6.6, p = 0.04) and a 20.0% rise in plasma adiponectin against a 12.0% fall on placebo (p < 0.001).

The cleanest trial
Agaricus blazei extract lowered insulin resistance in type 2 diabetes

Hsu C-H et al. (2007) · Journal of Alternative and Complementary Medicine

Population
60 analyzed Chinese adults with type 2 diabetes for over 1 year, already stable on gliclazide and metformin
Intervention
1500 mg/day Agaricus blazei extract for 12 weeks
Comparator
Cellulose placebo, double-blind
Finding
HOMA-IR 3.6 (SD 2.5) vs 6.6 (SD 7.4), p = 0.04. Plasma adiponectin +20.0% vs −12.0%, p < 0.001.

positive The only trial here that tested Agaricus blazei alone, was properly randomized and blinded, and met its primary endpoint. HOMA-IR is a surrogate marker, not a clinical outcome — no complication, event, or symptom endpoint was measured, and the trial ran 12 weeks at a single center.

Hsu et al., J Altern Complement Med, 2007 (RTHM-00216, PMID 17309383)

Ohno 2011: Phase I safety study (Japanese cancer patients in remission)

Ohno and colleagues published the first Phase I clinical study of ABM as a dietary supplement, giving 78 cancer survivors 1.8, 3.6, or 5.4 g/day of ABM granulated powder for six months.[10] Adverse events occurred in 9 patients (12%), mostly digestive — nausea and diarrhea — with one patient developing a liver dysfunction-related food allergy. None occurred in a dose-dependent manner. The authors conclude that ABM "does not cause problems in most patients within laboratory parameters at the dosages tested," while explicitly excluding possible allergic reaction from that reassurance.

This trial is frequently cited as having also shown NK cell or immune enhancement. It did not. It is a safety and tolerability study, and it reports no immune efficacy outcome.

Tangen 2015: Multiple myeloma (high-dose chemotherapy + stem cell transplant)

Forty multiple myeloma patients undergoing high-dose chemotherapy with autologous stem cell support were randomized double-blind to AndoSan (19 patients) or placebo (21), for roughly seven weeks.[11] AndoSan is 82% Agaricus blazei, with Hericium erinaceus and Grifola frondosa making up the rest — so this is a mushroom blend, not ABM alone. The AndoSan group showed increased regulatory T cells and plasmacytoid dendritic cells in the leukapheresis product, higher serum IL-1ra, IL-5 and IL-7, and increased expression of immunoglobulin, KIR, and HLA genes.

The sentence that rarely travels with those results is the trial's own: "There were no statistically significant differences in treatment response, overall survival, and time to new treatment." For a myeloma patient, those three are the endpoints that matter. It is also worth noting that increased regulatory T cells are not self-evidently good news in a cancer setting, since Tregs suppress anti-tumor immunity — the paper reports the change, it does not establish it as a benefit.

Kim 2025: Non-small cell lung cancer post-surgery (multicenter)

The most recent trial is a randomized, double-blind, placebo-controlled multicenter pilot in 66 patients with stage I–III non-small cell lung cancer, treated for 28 days after curative resection.[12] The intervention was a multivitamin and mineral complex containing Agaricus blazei, which means no result from it can be attributed to the mushroom rather than to the vitamins, the minerals, or the combination.

Its primary endpoint was natural killer cell activity recovery, and it was not met: "Although the increase in NKA was not statistically significant, the treatment group showed a greater relative recovery (17.8% vs. 9.9%, p = 0.104)." Secondary immune measures did separate — better preservation of T cells (p = 0.026) and B cells (p = 0.001), greater reduction in monocytes (p = 0.031) — but there were no differences in cytokines, BMI, ECOG performance status, or patient-reported outcomes. The authors' own conclusion is appropriately hedged: the complex "may contribute to favorable immune modulation," and "larger long-term trials are warranted."

Evidence position
Where Agaricus blazei actually sits
  1. Cell and receptor studiescompleted

    Extensive. Beta-glucan receptor work (Kasai 2004, Liu 2015) is real but reaches conflicting conclusions using different preparations.

  2. Animal studiescompleted

    Large and mostly positive across tumor, allergy, liver, and metabolic models, though not uniformly — Xu 2024 found ABM polysaccharide inhibited intraperitoneal but not subcutaneous tumors in the same experiment.

  3. Human case reportscompleted

    Includes the harm signal: three severe hepatic damage cases with two deaths (Mukai 2006) and two RUCAM-confirmed DILI cases (Hisamochi 2013).

  4. Small human trialscurrent

    Four trials, 40–100 patients each. One met its primary endpoint testing ABM alone (Hsu 2007). Two tested multi-ingredient products.

  5. Large randomized trialsmissing

    None. No adequately powered trial of a standardized Agaricus blazei preparation against a clinical endpoint exists.

  6. Meta-analysis of RCTsmissing

    Not possible — the existing trials use different preparations, populations, and endpoints, so there is nothing comparable to pool.

Agaricus blazei has genuinely reached human trials, which puts it ahead of most supplement mushrooms. But it has stalled at the small-trial rung for nearly two decades, and the trials that exist do not share a preparation. Hetland's 2020 review calls for exactly what is missing: studies with 'quality-controlled and standardized mushroom extracts, or fractions thereof, in randomized clinical studies powered to show putative therapeutic effects.'

Hsu 2007 (PMID 17309383); Tangen 2015 (PMID 25664323); Kim 2025 (PMID 41595590); Mukai 2006 (PMID 17105737); Hetland 2020 (PMID 32397163)

For the full clinical cancer evidence in depth, see Agaricus blazei and Cancer: Research from Brazil and Japan.

For NK cell activation evidence specifically, see Agaricus blazei and NK Cell Activation: Research Review.

For blood sugar effects, see Agaricus blazei and Blood Sugar: Hypoglycemic Effects.

How ABM Compares to Lion's Mane and Maitake

A natural question for someone already familiar with medicinal mushrooms is how Agaricus blazei compares to better-known species. Hetland and colleagues' 2020 review is the paper usually cited for the answer, and it does discuss ABM alongside Lion's Mane (Hericium erinaceus) and Maitake (Grifola frondosa) across tumor, inflammation, and allergy domains.[4]

It is worth being precise about what that paper is, because it is frequently overstated. It is a narrative review of preclinical and clinical findings, not a head-to-head comparison, and it does not rank the three mushrooms or conclude that ABM is strongest. Its actual conclusion is that all three "possess valuable antitumor, anti-inflammatory and antiallergic properties" and that these "should be investigated more thoroughly with quality-controlled and standardized mushroom extracts, or fractions thereof, in randomized clinical studies powered to show putative therapeutic effects." That is a call for better trials, not a verdict that the trials so far have settled anything. It is also the review whose senior author holds a stake in the AndoSan distributor.

Fact check

Is Agaricus blazei the best-evidenced immune mushroom?

The claim

“A 2020 comparative review found Agaricus blazei had the strongest and most consistently documented clinical immune modulation of the major medicinal mushrooms, beating Lion's Mane and Maitake head to head.”

A widely repeated paraphrase of Hetland et al., Int J Mol Sci, 2020.

What research shows

Unsupported

Hetland 2020 is a narrative review, not a head-to-head comparison. It performs no ranking and names no winner. Its conclusion is that all three mushrooms have properties worth investigating 'more thoroughly with quality-controlled and standardized mushroom extracts... in randomized clinical studies powered to show putative therapeutic effects.'

No study has compared these mushrooms against each other in humans. Their evidence bases differ mainly in which research communities pursued them, not in demonstrated superiority. The review's senior author is a cofounder and shareholder of the company distributing the ABM extract discussed.

Hetland et al., Int J Mol Sci, 2020 (RTHM-01201, PMID 32397163)

What can be said fairly is narrower: Agaricus blazei has more human trial data than most supplement mushrooms, Lion's Mane has the stronger neurological and cognitive literature, and Maitake has good preclinical evidence with some clinical data. None of that establishes a ranking, and the evidence landscape for each species reflects which research communities pursued it most intensively as much as anything about the mushrooms themselves.

For a comparison with Maitake's bioactive compounds specifically, see Maitake Bioactive Compounds: D-Fraction, MD-Fraction, and Beta-Glucans.

Beyond Immune Health: Liver, Blood Sugar, and Inflammation Research

The Th1/Th2 mechanism and the clinical RCT record are the headline story for ABM, but the research extends into several other health domains.

Liver — protection in animals, injury in humans: This is the domain where the animal literature and the human literature point in opposite directions, and where a pillar article has to say so plainly. In rodents, ABM has repeatedly shown hepatoprotective effects against chemically induced liver damage, with proposed mechanisms including antioxidant activity, reduced lipid peroxidation, and modulation of inflammatory pathways in liver tissue.

In people, the published reports run the other way. Mukai and colleagues described three patients with advanced cancer who developed severe hepatic damage while taking Agaricus blazei extract; two died of fulminant hepatitis.[15] In one patient, liver function recovered after stopping the extract and deteriorated again when she resumed it — a positive dechallenge/rechallenge, which is among the stronger forms of causal evidence available in a case report. Hisamochi and colleagues later reported two further cases of drug-induced liver injury confirmed by the Roussel Uclaf Causality Assessment Method, with liver histology closely resembling autoimmune hepatitis, and suggested "the immunostimulating action of ABM caused liver injury."[16]

These are case reports, not incidence data, and hundreds of thousands of Japanese consumers used ABM through the 1990s without a comparable signal being detected.[10] Both facts are true at once: severe events are evidently rare, and every severe human event reported for this mushroom has been hepatic. For the full evidence, see Agaricus blazei and Liver Protection: Research Review.

Safety

Critical

Reported liver injury, including two deaths

Concern

Five published cases of severe hepatic injury in people taking Agaricus blazei extract. Mukai 2006 reported three advanced cancer patients with severe hepatic damage, two of whom died of fulminant hepatitis, including one case with a positive dechallenge and rechallenge. Hisamochi 2013 reported two further RUCAM-confirmed drug-induced liver injury cases with histology resembling autoimmune hepatitis.

What the research says

These are case reports and cannot establish incidence; ABM was used by hundreds of thousands of Japanese consumers across the 1990s without a comparable signal emerging, and the Phase I study found adverse events in 12% of 78 patients, mostly digestive. But the harm that has been reported is consistently liver-related, and the proposed mechanism — immune stimulation driving an autoimmune-hepatitis-like picture — is the same mechanism the supplement is sold for.

Particularly relevant for: Highest concern for people with existing liver disease, people on hepatotoxic drugs or chemotherapy, and people taking immunosuppressants, where immune stimulation is working against the treatment.

What to do

Do not start Agaricus blazei during cancer treatment, or alongside immunosuppressant or hepatotoxic medication, without telling the treating physician. Mukai's patients had not disclosed their supplement use, which is precisely what made the liver injuries hard to diagnose. Stop and seek medical attention for jaundice, dark urine, persistent nausea, or right-upper-abdominal pain.

Mukai et al., Jpn J Clin Oncol, 2006 (RTHM-00196, PMID 17105737); Hisamochi et al., Clin J Gastroenterol, 2013 (RTHM-00522, PMID 26181451); Ohno et al., 2011 (RTHM-00427, PMID 21584278)

Blood sugar control: Beyond the Hsu 2007 RCT data on type 2 diabetes, preclinical research has characterized multiple mechanisms by which ABM may affect blood glucose: alpha-glucosidase inhibition (slowing carbohydrate digestion), insulin sensitization effects, and anti-inflammatory action that may reduce insulin resistance. For details, see Agaricus blazei and Blood Sugar: Hypoglycemic Effects.

Recent cancer mechanism research: Xu and colleagues' 2024 study found that ABM polysaccharide significantly promoted CD8+ T cell activity and colorectal cancer killing function in co-culture (p < 0.05).[14] The in vivo result was more mixed than that sentence suggests: the polysaccharide "could inhibit the growth of intraperitoneal but not subcutaneous tumors" in the same study. This is mechanistic work in cells and mice, not confirmation of a clinical effect. Their 2025 study added an important calibration: ABM polysaccharide anticancer efficacy varies with host age in animal models, with younger subjects showing stronger responses, a finding that has implications for interpreting the translational value of animal research that typically uses young animals.[13]

For the research on beta-glucan immune activation mechanisms that underpins much of ABM's effects, see How 1,3/1,6 Beta-Glucans Activate Your Immune System.

The Agaritine Question: Still Open

Agaricus blazei contains agaritine, a hydrazine derivative found in edible Agaricus species including common button mushrooms (A. bisporus). Agaritine has been studied as a potential carcinogen because hydrazine compounds can be mutagenic in certain assay systems.

The article most often cited on this question is Firenzuoli and colleagues' 2008 review, and it is worth quoting rather than paraphrasing, because it is regularly cited as reassurance when it says the opposite.[1] Firenzuoli writes that "clinical studies are positive confirmations, but we are still at the beginning, and there are perplexing concerns especially relative to the content of agaritine," which is "a well-known carcinogenic and toxic substance in animals, that must be completely and fully evaluated." That is a call for evaluation, not a clearance.

The question also had a real regulatory consequence. Following the 2006 case reports of hepatic injury, the Japanese Food Safety Committee evaluated commercial ABM products. In a preliminary genetic toxicity screen, one of three products tested came back Ames-positive; the result was made public by the Ministry of Health, Labor and Welfare on 13 February 2006, and that product was voluntarily withdrawn from the market with no further production, while the other manufacturers continued selling.[10] Ohno and colleagues are pointed about the process, describing the finding as "hastily announced by officials without further validation of the preliminary Ames' test results," and note that two-year chronic carcinogenicity studies of both A. blazei and A. bisporus have returned negative results.

Where that leaves a reader: agaritine content varies substantially between products, it is reduced by heat and drying, long-term animal carcinogenicity studies have been negative, and no human cancer has been attributed to it. It is also not settled, one product did fail a mutagenicity screen, and the review most cited on the topic explicitly asks for full evaluation rather than declaring the matter closed.

This safety question is examined in depth, with the most current evidence, in The Agaritine Controversy: Carcinogen or Harmless?.

Reading the Evidence Honestly

Agaricus blazei genuinely has more human data behind it than most supplement mushrooms. That is the fair version of the positive case, and it is worth something: four human trials, a Phase I safety study, a large animal literature, and a coherent proposed mechanism are more than Lion's Mane or Maitake can show for immune endpoints.

The unfair version is the one in circulation. Counted carefully, the record is one properly randomized, double-blind, placebo-controlled trial of Agaricus blazei alone that met its primary endpoint — a 60-patient, 12-week diabetes trial measuring a surrogate marker. The myeloma trial found no difference in treatment response, survival, or time to new treatment. The lung cancer trial missed its primary endpoint and tested a multivitamin complex rather than the mushroom. The gynecological cancer trial describes no randomization procedure. The triple-receptor mechanism story is contradicted by the paper it cites. And the most confident reviews come from a group with a commercial interest in the extract.

Firenzuoli's 2008 summary remains the most accurate sentence anyone has written about this mushroom: "Clinical studies are positive confirmations, but we are still at the beginning, and there are perplexing concerns especially relative to the content of agaritine."[1] Eighteen years later, the trials it called for still have not been run. Hetland's 2020 review asks for the same thing — standardized extracts in adequately powered randomized studies — and that gap, not the absence of interest, is what keeps Agaricus blazei where it is.[4]

Agaricus blazei is not an approved treatment for any condition, and nothing here is medical advice. What it is: a well-characterized mushroom with a plausible immune mechanism, one clean human result in insulin resistance, a wide preclinical literature, a documented capacity to cause serious liver injury in a small number of people, and an unresolved question about agaritine. Anyone considering it during cancer treatment, alongside immunosuppressants, or with existing liver disease should be discussing it with their physician rather than a supplement label.

For a dosage overview, see Agaricus blazei Dosage Guide: How Much to Take.

For the NK cell evidence specifically, see Royal Sun Mushroom and NK Cell Enhancement in Cancer Patients.

The Bottom Line

Agaricus blazei (Royal Sun Mushroom, Himematsutake) has more human data than most supplement mushrooms, but far less than the "four RCTs" headline implies. Two of those four tested multi-ingredient products rather than the mushroom alone; the myeloma trial found no difference in treatment response or survival; the 2025 lung cancer trial missed its primary endpoint. The one clean result is Hsu 2007, where ABM extract lowered HOMA-IR insulin resistance (3.6 vs 6.6, p = 0.04) in 60 type 2 diabetes patients. The popular triple-receptor mechanism claim is contradicted by the paper usually cited for it, and the most confident reviews share an author who is a shareholder in the extract's distributor. Against that sits a real safety file: five published cases of severe hepatic injury including two deaths, and an unresolved agaritine question that triggered a 2006 Japanese product withdrawal.

Frequently Asked Questions

Sources & References

  1. 1RTHM-00131·Firenzuoli, F et al. (2008). “The Medicinal Mushroom Agaricus blazei Murrill: Review of Literature and Pharmaco-Toxicological Problems..” Evidence-based complementary and alternative medicine : eCAM.Study breakdown →PubMed →↩
  2. 2RTHM-00215·Hetland, Geir et al. (2011). “The Mushroom Agaricus blazei Murill Elicits Medicinal Effects on Tumor, Infection, Allergy, and Inflammation through Its Modulation of Innate Immunity and Amelioration of Th1/Th2 Imbalance and Inflammation..” Advances in pharmacological sciences.Study breakdown →PubMed →↩
  3. 3RTHM-00468·da Silva de Souza, Aline Cristine et al. (2017). “Agaricus blazei Bioactive Compounds and their Effects on Human Health: Benefits and Controversies..” Current pharmaceutical design.Study breakdown →PubMed →↩
  4. 4RTHM-00620·Hetland, Geir et al. (2020). “Antitumor, Anti-Inflammatory and Antiallergic Effects of Agaricus blazei Mushroom Extract and the Related Medicinal Basidiomycetes Mushrooms, Hericium erinaceus and Grifola frondosa: A Review of Preclinical and Clinical Studies..” Nutrients.Study breakdown →PubMed →↩
  5. 5RTHM-00765·Huang, Kaiyuan et al. (2022). “Critical review on chemical compositions and health-promoting effects of mushroom Agaricus blazei Murill..” Current research in food science.Study breakdown →PubMed →↩
  6. 6RTHM-00081·Kerrigan, Richard W (2005). “Agaricus subrufescens, a cultivated edible and medicinal mushroom, and its synonyms..” Mycologia.Study breakdown →PubMed →↩
  7. 7RTHM-00561·Wang, Hang et al. (2013). “The Medicinal Values of Culinary-Medicinal Royal Sun Mushroom (Agaricus blazei Murrill)..” Evidence-based complementary and alternative medicine : eCAM.Study breakdown →PubMed →↩
  8. 8RTHM-00066·Ahn, W-S et al. (2004). “Natural killer cell activity and quality of life were improved by consumption of a mushroom extract, Agaricus blazei Murill Kyowa, in gynecological cancer patients undergoing chemotherapy..” International journal of gynecological cancer : official journal of the International Gynecological Cancer Society.Study breakdown →PubMed →↩
  9. 9RTHM-00114·Hsu, Chung-Hua et al. (2007). “The mushroom Agaricus Blazei Murill in combination with metformin and gliclazide improves insulin resistance in type 2 diabetes: a randomized, double-blinded, and placebo-controlled clinical trial..” Journal of alternative and complementary medicine (New York.Study breakdown →PubMed →↩
  10. 10RTHM-00229·Ohno, Satoshi et al. (2011). “Phase I Clinical Study of the Dietary Supplement, Agaricus blazei Murill, in Cancer Patients in Remission..” Evidence-based complementary and alternative medicine : eCAM.Study breakdown →PubMed →↩
  11. 11RTHM-00404·Tangen, Jon-Magnus et al. (2015). “Immunomodulatory effects of the Agaricus blazei Murrill-based mushroom extract AndoSan in patients with multiple myeloma undergoing high dose chemotherapy and autologous stem cell transplantation: a randomized, double blinded clinical study..” BioMed research international.Study breakdown →PubMed →↩
  12. 12RTHM-00928·Kim, Jiwon et al. (2025). “Immunomodulatory Effects of Multivitamin Complexes Containing Agaricus blazei in Patients Undergoing Curative Resection for Non-Small-Cell Lung Cancer: A Randomized, Double-Blind, Placebo-Controlled Multicenter Pilot Trial..” Biomedicines.Study breakdown →PubMed →↩
  13. 13RTHM-00955·Xu, Yongzhao et al. (2025). “The Age-Dependent Anticancer Efficacy of Agaricus blazei Murill Polysaccharide in Colon Cancer..” Molecular nutrition & food research.Study breakdown →PubMed →↩
  14. 14RTHM-00916·Xu, Yongzhao et al. (2024). “Preventive intervention with Agaricus blazei murill polysaccharide exerts anti-tumor immune effect on intraperitoneal metastasis colorectal cancer..” International journal of biological macromolecules.Study breakdown →PubMed →↩
  15. 15RTHM-00105·Mukai, Hirofumi et al. (2006). “An alternative medicine, Agaricus blazei, may have induced severe hepatic dysfunction in cancer patients..” Japanese journal of clinical oncology.Study breakdown →PubMed →↩
  16. 16RTHM-00287·Hisamochi, Akiko et al. (2013). “Drug-induced liver injury associated with Agaricus blazei Murill which is very similar to autoimmune hepatitis..” Clinical journal of gastroenterology.Study breakdown →PubMed →↩
  17. 17RTHM-00071·Kasai, H et al. (2004). “IL-12 Production Induced by Agaricus blazei Fraction H (ABH) Involves Toll-like Receptor (TLR)..” Evidence-based complementary and alternative medicine : eCAM.Study breakdown →PubMed →↩
  18. 18RTHM-00395·Liu, Yi et al. (2015). “Polysaccharide Agaricus blazei Murill stimulates myeloid derived suppressor cell differentiation from M2 to M1 type, which mediates inhibition of tumour immune-evasion via the Toll-like receptor 2 pathway..” Immunology.Study breakdown →PubMed →↩
  19. 19RTHM-00133·Hetland, G et al. (2008). “Effects of the medicinal mushroom Agaricus blazei Murill on immunity, infection and cancer..” Scandinavian journal of immunology.Study breakdown →PubMed →↩
  20. 20RTHM-00271·Wisitrassameewong, Komsit et al. (2012). “Agaricus subrufescens: A review..” Saudi journal of biological sciences.Study breakdown →PubMed →↩