The short answer
PSK, a turkey tail extract, is an approved add-on to chemotherapy in Japan. In the US no mushroom product is approved or established as cancer treatment, and supplements can interact with care.
Polysaccharide-K (PSK), from turkey tail, is an approved cancer product in Japan and has been given alongside chemotherapy since the mid-1970s, mainly after surgery for gastric or colorectal cancer.
Japanese meta-analyses of randomised trials report modest survival gains when PSK is added to chemotherapy, including a hazard ratio of 0.88 in pooled gastric cancer data.
That evidence describes a regulated, standardised extract used as an addition to chemotherapy, not capsules bought online.
NCI states the FDA has not approved turkey tail, PSK or reishi as a treatment for cancer or any other condition; in the US they are sold as dietary supplements.
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The full explanation.
The claim
Reishi, turkey tail, chaga, maitake and lion's mane are sold as capsules, powders and coffee blends, often with claims that they boost immunity, shrink tumours or treat cancer. Prices are high and the language borrows heavily from real research.
Why the idea appeals
The appeal here is unusually well founded, which is what makes it tricky. Mushroom compounds have been studied seriously for decades, some are used in cancer care in other countries, and several cancer drugs did originate in nature. When a seller says "there is research behind this", they are not always lying. The gap is between research existing and a product being proven.
What is actually used, and where
Polysaccharide-K, known as PSK or krestin, is an extract of turkey tail (Trametes versicolor). In Japan it is an approved product used in cancer treatment and has been given alongside chemotherapy since the mid-1970s, usually after surgery for gastric or colorectal cancer. Meta-analyses of randomised trials there have reported modest survival benefits when PSK is added to chemotherapy — around a 12% relative reduction in the risk of death in one pooled gastric cancer analysis.
That is a real finding, and it is narrower than it sounds. It describes a standardised pharmaceutical-grade extract, given as an addition to chemotherapy, in specific cancers, in a healthcare system that regulates it as a drug. It says nothing about capsules bought online.
In the United States, the picture is different. NCI states that the FDA has not approved turkey tail, PSK or reishi as a treatment for cancer or any other condition. They are sold as dietary supplements, which means they are not reviewed for effectiveness before sale, and NCI notes that batches and brands may not be the same as one another. Reishi is used in China to support the immune system of people having chemotherapy or radiotherapy; the trials behind that use are small and often measure immune markers rather than survival or symptoms.
The risks worth knowing
Mushroom supplements are not automatically gentle. Reishi is the best-documented example: it can increase bleeding risk alongside anticoagulants, its polysaccharides inhibit liver enzymes including CYP3A that many chemotherapy drugs depend on, it can enhance immune response in ways that matter if you take immunosuppressants, and rare cases of liver toxicity have been reported. Reishi spore powder can also raise the tumour marker CA72-4, which can muddy the results your team is using to track you. Because supplements are not tested batch by batch, what is in the jar may not match the label.
None of that means a mushroom supplement will harm you. It means your oncology team and pharmacist cannot assess the interaction unless they know what you are taking. Bring the label to your appointment.
What this does not mean
It does not mean mushroom research is quackery — PSK is genuine pharmacology and remains under study. It does not mean culinary mushrooms are a problem; eating them is fine and they are a perfectly good food. And it does not mean anyone who has taken a supplement has made a mistake.
What it does mean is that no mushroom product is an established cancer treatment in the United States, and nothing here should displace treatment that is.
The bottom line
Turkey tail's PSK has a real, limited role as an add-on to chemotherapy in Japan. No mushroom product has been shown to treat cancer on its own, and none is approved for cancer in the US. If you want to try one, the sensible route is through your care team, who can check it against your drugs and your blood counts before you spend anything.
Sources
Words to know
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Common questions
Is turkey tail an approved cancer treatment?
In Japan, PSK, an extract of turkey tail, is an approved product used in cancer treatment and given with chemotherapy. In the United States, NCI states the FDA has not approved turkey tail or PSK as a treatment for cancer or any other condition; they are sold as dietary supplements.
Are mushroom supplements safe to take alongside chemotherapy?
Not automatically. Reishi can increase bleeding risk, can inhibit liver enzymes such as CYP3A that many chemotherapy drugs rely on, and can enhance immune response, which matters with immunosuppressants. Ask your oncology team or pharmacist and show them the label before you start.
Is the supplement I can buy the same as the PSK used in Japan?
Almost certainly not. PSK is a standardised, pharmaceutical-grade extract regulated as a drug. NCI notes that in the US supplements are not reviewed for effectiveness before sale and that batches and brands may not be the same as one another.
What about reishi for immune support?
Reishi is used in China to support the immune system of people having chemotherapy or radiotherapy, but the trials are small and often measure immune markers rather than survival or symptoms. The FDA has not approved it as a cancer treatment.
Are mushrooms in food a problem?
No. Eating culinary mushrooms is fine and they are a perfectly good food. The questions on this page are about concentrated extracts and supplements taken at high doses.
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Written by: Cancer Explained Editorial TeamSources last checked: 2026-07-30Last updated: 2026-07-30Next planned review: 2028-07-29
How this page was created
Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes. We do not employ clinicians and do not intend to — our work is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
Editorial status — Source verified. This page was created with AI assistance and checked against the sources listed on it. Source checking is not a medical review.
General education. Low-risk educational or organizational content. Medical facts are cited to authoritative sources.
Human medical review: not completed. Cancer Explained is not clinician-reviewed, and that is a deliberate design choice rather than a gap we are waiting to close. We restate published federal guidance and cite it; the authority belongs to the source, not to us. That is why every page names where its claims come from — so you can verify us instead of trusting us. Use it to understand your situation and to ask better questions of the people treating you.
How this page was created
Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes. We do not employ clinicians and do not intend to — our work is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
Editorial status: Source verified — This page was created with AI assistance and checked against the sources listed on it. Source checking is not a medical review.
Human medical review: not completed. Cancer Explained is not clinician-reviewed, and that is a deliberate design choice rather than a gap we are waiting to close. We restate published federal guidance and cite it; the authority belongs to the source, not to us. That is why every page names where its claims come from — so you can verify us instead of trusting us. Use it to understand your situation and to ask better questions of the people treating you.
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