Adverse effects from PSK have not been reported since clinical trials began in Japan since 1970. In general, patients treated with chemotherapy or/and radiotherapy together with oral PSK experienced less or similar side effects than those treated with chemotherapy or/and radiotherapy alone9,18,19,26. However, symptoms such as coughing, nail pigmentation, constipation and diarrhoea have been reported9,32.
These side effects were significantly reduced when PSK was formulated in tablets or capsules instead of the medication given as a powder form reconstituted in water9.
Low grade gastrointestinal and haematological toxicities such as loss of appetite, nausea, vomiting, diarrhoea and stomatitis have been reported, but they were due to chemotherapeutic agents and radiation themselves18,19. In fact, toxicity occurred after surgery in a majority of patients who were on chemotherapy without PSK19.
In a Japanese Ministry of Health and Welfare Report, side effects were experienced in 114 patients of a total of 11,300 cancer patients administered PSK (1.01%)33. The main symptoms reported were diarrhoea and nausea.
Overall, oral PSK plus chemotherapy have less frequent and lower grade toxicity than that reported in other large randomised trials with standard chemotherapy34-37.