Moderate evidenceImmunity

Turkey Tail Mushroom

The strongest human evidence for any medicinal mushroom — but it belongs to PSK (krestin), a standardized prescription extract used as adjuvant cancer therapy in Japan, not to the mushroom powder sold as an immune supplement.

What the science says

Adjuvant therapy after curative gastric cancer resection Moderate evidence
A meta-analysis of 8 centrally randomized controlled trials with 8,009 patients found that adding PSK to chemotherapy after curative gastric cancer resection improved overall survival, hazard ratio 0.88 (95% CI 0.79-0.98, p = 0.018), with no significant heterogeneity. PSK is an approved pharmaceutical in Japan given under oncologist supervision — this result does not transfer to over-the-counter mushroom powder.
Immune parameters in cancer patients Limited evidence
A phase 1 dose-escalation trial in 9 women who had completed breast cancer radiotherapy found 3, 6, or 9 g/day of a Trametes versicolor preparation for 6 weeks was well tolerated, with trends toward higher lymphocyte counts and NK-cell activity and dose-related rises in CD8+ T cells and CD19+ B cells. This was uncontrolled, tiny, and designed to assess tolerability rather than efficacy.
Immune support in healthy people Limited evidence
No trial shows that turkey tail reduces colds, infections, or sick days in healthy adults. Generalising a cancer-adjuvant drug result to everyday immune support is not supported by any evidence.

Dosage & safety

Studied dosePSK oncology protocols used 3 g/day of the standardized protein-bound polysaccharide alongside chemotherapy. Supplement research has used 3-9 g/day of Trametes versicolor preparation. Most consumer products are mycelium grown on grain and contain mostly starch with little of the beta-glucan fraction studied — look for fruiting-body sourcing and a declared beta-glucan (not just polysaccharide) content.

SafetyWell tolerated overall; nausea, dark stools, and mild GI upset are most common. Mild, reversible liver enzyme elevations have been reported in oncology use of PSK. Because it modulates immune function, use caution in autoimmune disease and after organ transplant with immunosuppressants. Anyone with cancer should never substitute turkey tail for treatment, and should tell their oncologist before starting it — interactions with chemotherapy outside the tested PSK protocols are plausible and largely unstudied. Note that PSK is prescription-only in Japan and not approved as a drug in the US or EU.

Scientific references

Efficacy of adjuvant immunochemotherapy with polysaccharide K for patients with curative resections of gastric cancer
Oba K, Teramukai S, Kobayashi M, Matsui T, Kodera Y, Sakamoto J — Cancer Immunology, Immunotherapy, 2007
Phase 1 Clinical Trial of Trametes versicolor in Women with Breast Cancer
Torkelson CJ, Sweet E, Martzen MR, Sasagawa M, Wenner CA, Gay J, Putiri A, Standish LJ — ISRN Oncology, 2012

Where to buy

Swanson Vitamins, Turkey Tail Mushroom, 120 Capsules (500 mg per Capsule)

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