Turkey tail — named for its rings of brown and tan resembling a turkey's tail feathers — grows on dead logs worldwide and has been used in Traditional Chinese Medicine, where it's known as Yun Zhi, to treat lung-related conditions for centuries. Its most significant modern history, however, is distinctly Japanese: in the 1970s, Japanese researchers isolated polysaccharide-K (PSK, also called Krestin) from turkey tail and developed it into a formally approved adjunct cancer therapy.
PSK remains approved in Japan today as a supportive cancer treatment used alongside standard chemotherapy and surgery, though it has never received FDA or EMA approval, and in Western markets is sold only as an unregulated dietary supplement rather than an approved medicine.
Turkey tail has one of the more substantial human clinical trial records of any mushroom in this Atlas, specifically as PSK used alongside conventional cancer treatment in Japan. Multiple randomized controlled trials, including a study of 349 patients with stage II/III gastric cancer, found PSK added to standard treatment improved survival outcomes in patients at increased recurrence risk. Government-published cancer information (US National Cancer Institute's PDQ database) describes six randomized trials in lung cancer patients where PSK improved immune function, body weight, symptoms, or survival when added to chemotherapy.
The honest, necessary caveats: a comprehensive 2026 evidence review describes the overall quality as "low to moderate," noting many trials were conducted before contemporary chemotherapy regimens existed. Results aren't universally positive — one trial in head and neck cancer patients found no effect on recurrence risk. PSK is explicitly framed by reviewers as a supportive/adjunct agent, never a primary cancer treatment, and remains unapproved by the FDA. "Moderate" is the accurate, appropriately bounded rating — and it must never be understood as a substitute for oncologist-directed cancer treatment.
Traditionally simmered into tea or soup; PSK, its most-studied compound, is extracted and standardized for clinical/supplement use.