Up to June 2009, no Agaricus side effects have been reported in Japan due to the intake of Agaricus grown there. In Japan it has been extensively used as a dietary supplement since the mid 1990s, as well as the subject of intensive research since the mid 1960s.
Many researchers have studied Agaricus blazei, as well as other medicinal mushrooms for close to 50 years, due to laboratory tests, which showed its potential in both fighting cancer and the stimulation of the immune system, as well as its safety.
The large number of both in vitro and in vivo studies and the presence of similar results give good evidence to support the assert for inhibition of tumor growth and the stimulation of parts of the immune system. Most recent research confirmed that Agaricus is needed, safe and effective; therefore it becomes an obvious choice for supplementation.
Its safety is especially concerning, as it is considered one of the most popular complementary medicines among cancer patients. Since toxic heavy metals may be taken up and concentrated in mushrooms and funghi, it is important to be assured by the producer that the mushroom has not been grown on contaminated soil or substrate.
However, there are conflicting reports regarding the effect of ABM on liver function. There is one report marked in medical literature stating that three cancer patients who took an Agaricus supplement suffered from liver damage. The report mentions three cases of patients with advanced cancer who showed severe hepatic damage and despite the fact, that several other factors cannot be completely ruled out as the causes of liver damage, the link between the Agaricus blazei extract and liver damage was suggested.
On the other hand, study on ABM intake in patients with chronic hepatitis C virus infection performed by Grinde et al. did not show any side effects on the liver function . Patients in this study were administered with the AndoSan ABM extract, which proved its non hepatotoxic properties!
What is more, the intake of ABM in the form of AndoSan was tested in healthy volunteers and patients with inflammatory bowel diseases (IBD). A standardized daily dose of 60 ml  of ABM extract for 12 days, as well as a high daily dose of 360 ml during each of two days was evaluated in the context of safety. Collected data revealed no pathological effects at all on hematological parameters including those for liver, pancreatic and renal function. This has recently been confirmed in patients with IBD (ulcervative colitis and Crohn's disease) (Førland et al manuscript submitted) who ingested AndoSan for 2 weeks.
 Luiz RC, Jordão BQ, da Eira AF, Ribeiro LR, Mantovani MS, Mechanism of anticlastogenicity of Agaricus blazei Murill mushroom organic extracts in wild type CHO (K(1)) and repair deficient (xrs5) cells by chromosome aberration and sister chromatid exchange assays, 2003
 Pinheiro F, Faria RR, de Camargo JL, Spinardi-Barbisan AL, da Eira AF, Barbisan LF, Chemoprevention of preneoplastic liver foci development by dietary mushroom Agaricus blazei Murrill in the rat, 2003
 Mukai H, Watanabe T, Ando M, Katsumata N. , An Alternative Medicine, Agaricus blazei, May Have Induced Severe Hepatic Dysfunction in Cancer Patients.Japan J Clinical Oncology. 2006 Dec;36(12):808-10.
 Grinde B, Hetland G, Johnson E: Effects on gene expression and viral load of a medicinal extract from Agaricus blazei inpatients with chronic hepatitis C infection. Int Immunopharmacol 2006, 6:1311-1314.
 Johnson E, Førland DT, Sætre L, Bernardshaw SV, Lyberg T, Hetland G: Effect of an extract based on the medicinal mushroom Agaricus blazei Murill on release of cytokines, chemokines and leukocyte growth factors in human blood ex vivo and in vivo. Scand J Immunol 2009, 69:242-250