Supplement
Turkey Tail (Trametes versicolor / PSK)
Survival after curative surgery for colorectal or gastric cancer, with PSK (polysaccharide-K, a standardized prescription extract in Japan) added to older oral chemotherapy: pooled trials from the 1980s to 2000s were positive, and the three most recent trials found no benefit.
Grade C: human trials exist, but they are small, mixed or not yet repeated. This is not a finding that it does not work. How to read a grade →
Turkey tail is a mushroom. A purified extract called PSK is a prescription drug in Japan. Older Japanese studies found that people lived longer after surgery for colon or stomach cancer when PSK was added to chemotherapy. More recent studies found no gain. A careful review found a small benefit and judged the evidence weak.
- Dose studied
- PSK/PSP 1–3 g/day
- Form graded
- Trametes versicolor PSK/PSP
- Cited PMIDs PubMed ID: the permanent number the US National Library of Medicine gives a published paper. Each one links to that paper's record on PubMed.
- PMID 36445793 →
A letter describes the human evidence, not the product, the manufacturer, or the ingredient's worth.
See the full evidence record →Survival after colorectal or gastric cancer surgery with the PSK extract added to chemotherapy; older pooled trials positive, recent trials null.
Why this gradeGrade C, small or unreplicated trials. The reasoning, and what the grade does not cover.
Grade C on overall survival after curative resection of colorectal or gastric cancer, PSK added to chemotherapy. Older meta-analyses A study that pools the numbers from several trials into one combined estimate. of centrally randomized Japanese trials were positive (Sakamoto et al., 2006; PMID 16133112; Oba et al., 2007; PMID 17106715), and the 2022 Cochrane review found low-certainty evidence of a small five-year survival gain (PMID 36445793). The three most recent trials did not confirm a benefit (PMID 28634730; PMID 29094178; PMID 38307591). Mixed randomized evidence on regimens that are no longer standard is C.
WHAT THIS GRADE DOES NOT COVERimmune support in people without cancer, which no PSK trial tested; retail turkey tail products, which have not been shown equivalent to PSK; and use instead of cancer treatment.
A grade describes the human evidence for a named use. It is not advice, and it is not a judgment on any individual prescription. How the letters are decided →
Who responds: this record's trial reading reports no subgroup that identifies who responds.
How this letter has changed · latest: October 2026 · Corrected
The record graded immune measures, but its only citation, the Cochrane review (Pilkington et al., 2022; PMID 36445793), studied survival and adverse effects in colorectal cancer, not immune markers, and the ref did not say what it found. The endpoint is now overall survival after curative resection with PSK added to chemotherapy. Added: Sakamoto et al. (Cancer Immunol Immunother, 2006; PMID 16133112) and Oba et al. (Cancer Immunol Immunother, 2007; PMID 17106715), positive pooled survival; Miyake et al. (Surg Today, 2018; PMID 28634730), Okuno et al. (Cancer Chemother Pharmacol, 2018; PMID 29094178) and Ogawa et al. (Anticancer Res, 2024; PMID 38307591), null; Zhong et al. (Front Pharmacol, 2019; PMID 31333449), immune markers pooled with Ganoderma products. The dose field now states PSK at about 3 g/day and that retail products are not shown equivalent. C unchanged. Applied the written grade definition under the editor's standing instruction of October 2026 (Arnold Sandlow, D.C.).PMID 16133112 PMID 17106715 PMID 28634730 PMID 29094178 PMID 31333449 PMID 36445793 PMID 38307591
Every change to a letter on this site is dated and published. The full evidence log →
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As studied: PSK about 3 g/day by mouth alongside oral fluoropyrimidine chemotherapy after surgery, for months to years. Turkey tail mushroom powders and other extracts sold as supplements have not been shown equivalent to PSK.
Standardized forms were used in the cited trials; product quality varies.
The cited review does not report when doses were taken (PMID 36445793).
Checked against the published summary; the full paper could not be read. What the cited trials did, not a schedule. Every supplement, by trial timing →
Autoimmune disease. Pregnancy.
Immunosuppressants: the polysaccharide-K fraction is immune-active by design, which runs against the purpose of the drug. Its studied use is alongside chemotherapy under oncology supervision rather than instead of it, and that distinction is the whole caution.
Mechanism-based, no human interaction study located. The drug interactions described for Turkey Tail (Trametes versicolor / PSK) are mechanism-based. A PubMed search for human interaction, pharmacokinetic or co-administration studies pairing it with chemotherapy, immunosuppress, immunosuppressants returned no results in August 2026. The caution stands on pharmacology, not on a trial, and is labeled as such. Basis: pharmacological mechanism, not a human study. Searched PubMed in August 2026: 3 queries, 0 human results.
Under oncology supervision, the disease-specific endpoints of the trials: recurrence and survival. No immune marker is a validated stand-in for those outcomes. PSK (Krestin) is the standardized extract used in the Japanese trials; retail turkey tail products may not contain equivalent PSK.
Primary evidenceSeven papers, each linked to its PubMed record.
Sakamoto et al. (Cancer Immunol Immunother, 2006; PMID 16133112): meta-analysis of three centrally randomized Japanese trials, 1,094 patients after curative colorectal cancer resection; PSK with chemotherapy improved overall survival (risk ratio 0.71) and disease-free survival (0.72). Oba et al. (Cancer Immunol Immunother, 2007; PMID 17106715): eight randomized trials, 8,009 patients after gastric cancer resection; overall survival hazard ratio How often an event happened in the treated group compared with the control group over the same period. A ratio of 0.80 means 20 percent fewer events. 0.88. Pilkington et al. (Cochrane Database Syst Rev, 2022; PMID 36445793): seven trials, 1,569 patients with colorectal cancer; low-certainty evidence of a small five-year survival gain (RR 1.08, number needed to benefit 16) and very-low-certainty evidence on adverse effects, with chemotherapy regimens that are no longer standard. Recent trials did not confirm a benefit: Miyake et al. (Surg Today, 2018; PMID 28634730), MCSGO-CCTG, 357 patients, UFT with PSK failed non-inferiority to UFT with leucovorin (3-year disease-free survival 72.1 against 82.3 percent); Okuno et al. (Cancer Chemother Pharmacol, 2018; PMID 29094178), JFMC38, stage II rectal cancer, UFT with PSK against surgery alone, disease-free survival numerically worse, closed early; Ogawa et al. (Anticancer Res, 2024; PMID 38307591), 186 patients, adding PSK to UFT with leucovorin did not change 3-year disease-free survival. Zhong et al. (Front Pharmacol, 2019; PMID 31333449): the only pooled immune-marker data (CD3 and CD4 up, CD8 and NK cells unchanged), mixed with Ganoderma products, so it does not grade PSK alone. Funding of the older Japanese trials is not stated in the indexed records. Grade C: positive older pooled survival data on outdated regimens, with the recent trials null.
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How EBL searched for the trials (1 search)
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("polysaccharide K"[tiab] OR PSK[tiab] OR krestin[tiab] OR "Coriolus versicolor"[tiab] OR "Trametes versicolor"[tiab]) AND (randomized controlled trial[pt] OR meta-analysis[pt]) AND humans[mesh]Grades move when new trials publish. A free monthly email lists every grade EBL moved, with the reason and the trial behind it: the sign-up is on the Evidence Log →