PSK and PSP are two different polysaccharide-protein compounds extracted from turkey tail mushroom (Trametes versicolor, also called Coriolus versicolor). PSK, sold under the brand name Krestin, was developed and studied in Japan and has been approved there as an adjunctive cancer treatment since the mid-1970s. PSP was developed later in China and has a similar but not identical sugar structure. Neither compound is approved by the FDA to treat cancer in the United States, and neither is the same product as the turkey tail supplements sold over the counter.
Key Facts at a Glance
- PSK stands for polysaccharide-K, also known by the brand name Krestin. It is approved in Japan as an adjunct to standard cancer treatment.
- PSP stands for polysaccharopeptide. It was developed in China from a different strain of Trametes versicolor and differs from PSK in its sugar composition.
- Both compounds have been studied as additions to surgery, chemotherapy, or radiation, not as replacements for them.
- The strongest human evidence comes from Japanese randomized controlled trials of PSK in gastric, colorectal, and lung cancer.
- The FDA has not approved PSK, PSP, or any medicinal mushroom product to treat or prevent cancer.
- Retail turkey tail capsules and powders are not manufactured or regulated the same way as pharmaceutical-grade PSK.
PSK (Polysaccharide-K): The Japanese Clinical Research
PSK has the largest body of human clinical trial evidence of any medicinal mushroom compound. According to the National Cancer Institute’s review of complementary and alternative medicine research, a meta-analysis of eight randomized controlled trials involving more than 8,000 gastric cancer patients found that adding PSK to standard treatment improved overall survival, with a hazard ratio of 0.88. A separate 1994 Japanese trial reported that PSK improved both five-year disease-free survival and five-year overall survival rates compared with standard treatment alone.
In colorectal cancer, a pooled analysis of three trials covering over 1,000 patients found PSK was linked to better five-year survival when added to chemotherapy. In lung cancer, all six randomized controlled trials reviewed showed a benefit on at least one measured outcome, such as immune function, body weight, physical performance, symptom control, or survival. The National Cancer Institute also notes that PSK’s safety record in Japan is well established, with few reported adverse events and good patient tolerance across thousands of treated patients since the 1970s.
These trials were conducted in Japanese hospital settings, using a pharmaceutical-grade, standardized extract given alongside conventional treatment. They do not tell us how PSK performs as a standalone therapy, in non-Asian populations, or in cancer types outside the ones studied.
PSP (Polysaccharopeptide): The Chinese Research
PSP is a related but distinct extract from Trametes versicolor, developed in China. The National Cancer Institute describes PSP and PSK as differing somewhat in their sugar composition, meaning they are not interchangeable compounds even though both come from the same mushroom species. Published research on PSP includes smaller clinical studies, along with a larger body of laboratory and animal research on its immune-related activity.
Compared with PSK, the human clinical trial base for PSP is smaller and less consolidated in major reviews like the National Cancer Institute’s. That does not mean PSP lacks scientific interest, but it does mean readers should be more cautious about drawing firm conclusions from PSP research than from the larger PSK trial record.
PSK vs. PSP: A Side-by-Side Comparison
- Country of development: PSK comes from Japan. PSP comes from China.
- Regulatory status: PSK is approved as an adjunctive cancer treatment in Japan. PSP is used in China but is not FDA-approved.
- Clinical trial base: PSK has a large trial base, including several meta-analyses in gastric, colorectal, and lung cancer. PSP has a smaller trial base with fewer large randomized trials in major reviews.
- Composition: Both are polysaccharide-protein complexes, but they differ from each other in sugar composition.
- US legal status: Neither PSK nor PSP is FDA-approved for cancer treatment.
- Relationship to over-the-counter turkey tail supplements: Neither is equivalent to retail turkey tail products; both are produced as standardized, pharmaceutical-grade extracts.
Why Regulatory Status Differs Between Countries
Japan’s approval of PSK reflects its own national drug regulatory process, built on the clinical trial data generated there over several decades. China’s use of PSP similarly reflects its own regulatory framework and research history. Neither country’s approval process is the same as the FDA’s, and an approval in one country does not carry over to another.
In the United States, PSK and PSP have never gone through the FDA’s drug approval process for cancer treatment. Turkey tail products sold in the US are regulated as dietary supplements, not drugs. Under that framework, the FDA does not require manufacturers to prove a supplement is effective before it is sold, and product quality and content can vary between brands and even between batches of the same brand.
Pharmaceutical-Grade PSK Versus Over-the-Counter Turkey Tail Supplements
This is one of the most important distinctions in this entire topic. The PSK used in Japanese clinical trials is a standardized, pharmaceutical-grade extract manufactured under strict quality controls. The turkey tail capsules, powders, or tinctures sold in US health food stores or online are not the same product, even when the label mentions PSK or polysaccharides.
- Dietary supplements do not require FDA premarket testing for safety or effectiveness.
- Labeled ingredient amounts are not guaranteed to match what is actually in the product.
- Extraction methods, mushroom strains, and polysaccharide concentrations vary widely between brands.
- No over-the-counter turkey tail supplement has been tested in the large randomized trials described above.
Readers interested in how turkey tail is generally studied and used, outside the specific PSK and PSP research, can see our broader turkey tail mushroom research overview.
Evidence Limits: What This Research Does and Does Not Show
It’s easy to read impressive trial statistics and assume more than the data supports. Here is what the current evidence does and does not establish.
- The trials studied PSK and PSP as additions to standard treatment, not as substitutes for surgery, chemotherapy, or radiation.
- Most of the strongest trials were conducted decades ago in Japanese and Chinese hospital populations, which may not reflect outcomes in other countries or healthcare systems.
- Trial results apply to the specific pharmaceutical-grade extracts studied, not to any particular retail supplement brand.
- No study establishes that PSK or PSP cures cancer, prevents recurrence on its own, or works for every cancer type.
- The FDA has not approved medicinal mushroom compounds to treat, prevent, or cure any medical condition.
For a general framework on how to weigh laboratory, animal, and human evidence for any mushroom compound, see our evidence hierarchy guide. The immune-related mechanisms researchers propose for PSK and PSP are discussed further in our overview of mushrooms and immune function, and the related beta-glucan class of compounds is covered in our beta-glucan research profile.
Who Should Use Extra Caution
Anyone considering PSK, PSP, or turkey tail supplements alongside cancer treatment should talk with their oncology team first. Extra caution is warranted for people who are currently undergoing chemotherapy or radiation, people taking immunosuppressant medications, people with autoimmune conditions, people scheduled for surgery, and people who are pregnant or breastfeeding. Mushroom-derived compounds can interact with immune function and, in some cases, with other medications, so this decision should not be made without a qualified clinician who knows the person’s full medical history.
A Decision Path for Thinking Through This Research
- Identify whether you’re asking about PSK (Japan), PSP (China), or a generic over-the-counter turkey tail product. They are not the same thing.
- Check whether the evidence you’re looking at comes from human clinical trials, animal studies, or laboratory (in vitro) research. Human trial evidence is strongest for PSK in specific cancer types.
- Confirm the compound was studied as an addition to standard treatment, not as a replacement for it.
- Remember that no retail supplement has been tested in these trials, so trial results don’t transfer automatically to a product on a store shelf.
- Bring any questions about PSK, PSP, or turkey tail supplements to an oncologist or treating physician before making any treatment decisions.
Frequently Asked Questions
Is PSK the same thing as turkey tail mushroom powder?
No. PSK is a specific, standardized pharmaceutical-grade extract manufactured under strict quality controls in Japan. Turkey tail powders and capsules sold as dietary supplements are different products, even when they come from the same mushroom species.
Is PSK approved to treat cancer in the United States?
No. PSK is approved as an adjunctive cancer treatment in Japan, but the FDA has not approved PSK, PSP, or any medicinal mushroom product to treat, prevent, or cure cancer in the United States.
What’s the difference between PSK and PSP?
Both come from turkey tail mushroom, but PSK was developed in Japan and PSP was developed in China. According to the National Cancer Institute, they differ somewhat in their sugar composition, and PSK has a larger body of human clinical trial evidence behind it than PSP.
Can I use turkey tail supplements instead of chemotherapy?
No research supports replacing chemotherapy, radiation, or surgery with turkey tail supplements, PSK, or PSP. The clinical trials behind these compounds studied them as additions to standard treatment, not substitutes for it. Anyone considering this should speak with their oncology team.
Educational Disclaimer
This article is for general educational purposes only. It summarizes published research on PSK and PSP from turkey tail mushroom and is not medical advice, a treatment recommendation, or a substitute for care from a qualified physician or oncologist. Do not start, stop, or change any cancer treatment or medication based on this article. Always talk with a qualified healthcare provider before using any mushroom compound or supplement, especially alongside cancer treatment.