Why mushrooms in the COVID-19 context
The COVID-19 pandemic (SARS-CoV-2) sharpened interest in natural immunomodulators — substances able to "tune" the immune response without suppressing it. Among the candidates were β-glucans and other mushroom polysaccharides: long studied in oncology and infectious diseases, with a confirmed safety profile, and available as standardized supplements.
The team of Saxe, Stamets and Wilson at the Medicinal Fungi Conference (George Washington University, 2023) formulated the hypothesis: polypore mycelium (agarikon, trametes) may act as a broad-spectrum antiviral — through a combination of β-glucans, lectins, indole compounds and low-molecular-weight protease inhibitors. That hypothesis underpinned two 2026 RCTs.
Agarikon (Fomitopsis officinalis)
Agarikon — the larch polypore, a wood-decay fungus long used in the folk medicine of North America and Siberia. The detailed species card is at Agarikon (Laricifomes officinalis).
Agarikon extracts showed antiviral activity against influenza, herpes simplex, HIV and coronaviruses in preclinical models. At the 2023 conference Stamets presented data showing agarikon inhibits SARS-CoV-2 in a pseudovirus system.
FoTv: the agarikon–trametes combination
FoTv (Fomitopsis officinalis + Trametes versicolor) is a standardized blend of two polypore mycelia. The idea behind the combination: each fungus carries its own set of bioactive compounds, and synergy gives a broader spectrum of action.
RCT in active COVID-19
In 2026 a double-blind placebo-controlled RCT was published (Saxe G. et al., medRxiv):
- Design. Two-centre study (UCSD and UCLA), n=50 (26 FoTv, 24 placebo), patients with mild/moderate COVID-19, symptom duration ≤9 days.
- Dose. 8 capsules of 500 mg three times a day for 4 days.
- Results. FoTv statistically significantly reduced the number and severity of symptoms, especially sore throat and cough. The antiviral effect was confirmed in an in-vitro SARS-CoV-2 pseudovirus model.
- Safety. Excellent tolerability; no serious adverse events recorded.
- Registration: ClinicalTrials.gov NCT04667247.
Details in the card FoTv in active COVID-19.
RCT as a vaccine adjunct
The group's second double-blind RCT (BMC Immunology, 2026):
- Design. n=90 (52 FoTv, 38 placebo), 4 days of intake together with COVID-19 vaccination.
- Results. In "COVID-naive" participants (no prior viral exposure), FoTv significantly reduced vaccine side effects (days 3 and 5) and maintained or increased antibody levels over 6 months of follow-up.
- Registration: ClinicalTrials.gov NCT04951336.
Details in the card FoTv as a vaccine adjunct.
Trametes (Trametes versicolor)
Trametes versicolor, or "turkey tail", is one of the most studied fungi in oncology. The detailed species card is at Trametes versicolor. The PSK and PSP polysaccharides from trametes are registered in Japan and China as adjuvants for stomach, colon and lung cancer.
In the COVID-19 context, three directions are of interest:
- Immunomodulation. PSK increases NK-cell and γδ-T-lymphocyte activity, which may improve the antiviral response.
- Anti-inflammatory action. Trametes β-glucans reduce the excessive cytokine response ("cytokine storm") in animal models of sepsis.
- Microbiome. Trametes extracts modulate gut-microbiota composition, indirectly influencing immunity.
Reishi (Ganoderma lucidum)
Reishi — the "mushroom of immortality" of traditional Chinese medicine. The detailed card is at Reishi (Ganoderma lucidum). In laboratory conditions, reishi triterpenoids suppressed SARS-CoV-2 replication in cell lines. Reishi spore powder was studied in a human RCT (n=128) for insomnia and fatigue.
Shiitake (Lentinula edodes)
Shiitake — the most popular cultivated mushroom in the world. In the RCT by Dai et al. (2015), daily consumption of 5–10 g of dried shiitake (n=52) increased γδ-T-cell and NK-cell proliferation, raised secretory IgA and lowered C-reactive protein in healthy volunteers. Details in the card Shiitake: immunity and T-cells.
Lentinan — an isolated shiitake β-glucan — is registered in Japan as an adjuvant for gastric-cancer chemotherapy. Preliminary data on its antiviral activity exist.
Cordyceps
Cordyceps is traditionally used in Chinese medicine as a general tonic. In an RCT (Xiao et al., 2004), the Cs-4 strain improved VO₂max in the elderly. Cordyceps's cardiopulmonary effects may be relevant in post-COVID syndrome — shortness of breath, reduced exercise tolerance. Details in the card Cordyceps Cs-4 in the elderly.
Other fungi in the literature
The review by Saxe, Stamets and Wilson (2023) and subsequent publications mention:
- Agaricus blazei (almond mushroom) — increased IgG and reduced inflammation in the elderly;
- Hericium erinaceus (lion's mane) — neuroprotection and anti-inflammatory action in neuroinflammation models;
- Inonotus obliquus (chaga) — the extract inhibited SARS-CoV-2 replication in the Vero E6 cell line.
A critical view
Despite encouraging results, the use of mushrooms in COVID-19 should be viewed critically:
- Quality of evidence. The positive RCTs (FoTv) are so far single and pilot-scale. Independent replication is needed.
- Conflict of interest. The FoTv RCTs were funded with participation of Fungi Perfecti (Stamets). This does not invalidate the results but requires transparent assessment.
- No replacement for vaccination. No mushroom product replaces COVID-19 vaccination. In the RCTs FoTv acted as an adjuvant, not an alternative.
- Dose and form. Results were obtained for a specific form (mycelium, 500 mg capsules × 24/day). Fruiting-body extracts at other doses may have a different effect.
Conclusion
Mushroom β-glucans and mycelial complexes are a reasonable and safe complementary strategy for immune support, including in the context of viral infections. However, the evidence base in COVID-19 is at an early stage. The practical conclusion: mushroom supplements can complement but not replace standard antiviral and vaccination prophylaxis.