Benefits
Immune system activation
PSK and PSP activate dendritic cells, macrophages, and NK cells via Toll-like receptor and Dectin-1 signaling, enhancing both innate and adaptive immune responses.
PSK/Krestin is a prescription drug, distinct from supplements
PSK (Krestin) is a purified, protein-bound polysaccharide sold as a prescription pharmaceutical in Japan and is not the same product as over-the-counter turkey tail supplements. The oncology research applies to that regulated drug, and independent reviews rate its survival evidence as low-certainty. OTC turkey tail is used for general immune support and is not intended to treat, cure, or improve survival from any disease.
Gut microbiome support
Turkey tail acts as a prebiotic, selectively feeding Bifidobacterium and Lactobacillus species. Clinical study showed significant increases in beneficial bacteria and reduction in Clostridium after supplementation.
Antioxidant protection
Contains phenolic compounds and polysaccharides that show free-radical-scavenging activity in laboratory assays; clear antioxidant outcomes in humans are not well established.
Mechanism of action
TLR-2 and Dectin-1 activation
Beta-glucans in PSK and PSP bind pattern recognition receptors on macrophages and dendritic cells, triggering NF-κB activation and cytokine production that primes adaptive immune responses.
NK and T-cell augmentation
Turkey tail polysaccharides increase NK cell cytotoxicity and CD8+ T-cell activity, enhancing immune surveillance for abnormal or virus-infected cells.
Prebiotic fermentation
Polysaccharides from turkey tail are fermented by colonic microbiota, producing short-chain fatty acids and selectively feeding beneficial bacterial species, improving gut microbiome composition.
Clinical trials
Randomized controlled study of turkey tail polysaccharopeptide (PSP) extract (2.4–4.8 g/day) for 8 weeks in healthy adults.
24 healthy adults. 8-week supplementation.
In this small randomized trial (22 completers, with an amoxicillin comparator arm), PSP produced prebiotic-consistent microbiome shifts, though individual baseline composition largely dominated the response.
Cochrane systematic review and meta-analysis of Coriolus (Trametes) versicolor extract added to chemotherapy/radiotherapy in colorectal cancer (7 RCTs, 1,569 participants).
Multiple trials, hundreds of patients.
The review reported low-certainty evidence of a small improvement in five-year survival (risk ratio about 1.08) and very-low-certainty, uncertain effects on chemotherapy side effects, concluding the evidence is too uncertain for firm conclusions and that the chemo regimens used do not reflect current practice. This research concerns purified extract fractions used in oncology, which are distinct from over-the-counter turkey tail supplements.