Only a few clinical studies have assessed adverse events associated with maitake supplementation.
In one phase 1–2 clinical trial involving menopausal women with resected breast cancer, no severe side effects were reported. However, two of the 34 participants dropped out of the study due to adverse reactions. One participant experienced symptoms of nausea and joint pain (at a dosage of 1mg/kg per day), while another participant had an allergic reaction to the supplement (at a dosage of 10mg/kg per day).[1]
Finally, in one study, levels of the immunosuppressive cytokine IL-10 was increased after maitake supplementation[1], suggesting that it may not be suitable for individuals with cancer or a compromised immune system.