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 many supplements can change how treatment works.
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 randomized 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 one specific extract used as an addition to chemotherapy in Japan, 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.
On this page
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The whole article, with every detail and caution.
This page is for people who have seen mushroom supplements sold as cancer treatments. It explains what the research does and does not show, and the risks to discuss with your care team.
The claim
Reishi, turkey tail, chaga, maitake and lion's mane are sold as capsules, powders and coffee blends. The claims attached are big: they boost immunity, shrink tumors, or treat cancer. Prices are high, and the language borrows heavily from real research.
Why the idea appeals
The appeal here rests on something real, 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 start out in nature. So 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. It has been given alongside chemotherapy since the mid-1970s, usually after surgery for gastric or colorectal cancer. Meta-analyses of randomized trials there have reported modest survival benefits when PSK is added to chemotherapy. A 2007 pooled analysis of eight trials in gastric cancer found a hazard ratio for death of 0.88. That means a modest reduction in the risk of death.
That is a real finding. It is also narrower than it sounds. It describes one specific extract. It was given as an addition to chemotherapy, in specific cancers, in Japan. 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. NCI notes that the FDA does not regularly review how supplements are made, so 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 risks worth knowing
Mushroom supplements are not automatically harmless. NCI says many dietary supplements can change how cancer treatment works. Your care team cannot check for that unless they know what you take. Do not start a supplement during treatment without asking them first.
That does not mean a mushroom supplement will harm you. It means your oncology team and pharmacist need to 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 it remains under study. It is not about mushrooms eaten as ordinary food. And it does not mean anyone who has taken a supplement has made a mistake.
What it does mean is this. 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 but limited role as an add-on to chemotherapy in Japan. No mushroom product has been shown to treat cancer on its own. None is approved for cancer in the US. If you want to try one, the sensible route is through your care team. They can check it against your treatment before you spend anything.
Sources
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. NCI says many dietary supplements can change how cancer treatment works. Ask your oncology team or pharmacist, and show them the label, before you start. Do not start one on your own during treatment.
Is the supplement I can buy the same as the PSK used in Japan?
Not necessarily. PSK is a specific extract made by one company and approved in Japan. NCI notes that the FDA does not regularly review how supplements are made, so batches and brands may not be the same as one another.
What about reishi for immune support?
NCI says reishi is used in China to strengthen the immune system of people having chemotherapy or radiation. The FDA has not approved it as a treatment for cancer or any other condition.
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 ExplainedSources last checked: 2026-07-30 what this meansLast updated: 2026-09-29Next planned review: 2027-01-30
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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, and this 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 checked — This page was written with AI assistance and then compared with the sources listed on it, looking for statements those sources do not back up. That check is not a sentence-by-sentence record and can miss errors. It is not a medical review, and it does not confirm the page is complete or right for your situation.
Human medical review: not completed. Pages here are not signed off by a clinician before they publish. That is not an oversight we are quietly working around: we restate published guidance and cite it, so the authority belongs to the source rather than to us, and every page names where its claims come from — you can verify us instead of trusting us. Where a volunteer clinician has reviewed a page, their name and credentials appear on it; where no name appears, no clinician has checked it. We are glad to have reviewers and are recruiting them, and we do not hold pages back waiting for one. Use this site to understand your situation and to ask better questions of the people treating you.
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