Workers exposed to high levels of such spores have been known to develop an occupational disease known as Mushroom Worker's Lung. However, the relevance of such findings to the ingestion of mushrooms is uncertain. It has been associated with severe dermatitis. One publication described 51 such complications. The shiitake mushroom contains agaritine, a hydrazine that has been shown carcinogenic in animals.
Most studies report no side effects.
Because potential toxicity exists from mistaken mushroom identity, use caution when obtaining this particular natural product. Facts and Comparisons Review of Natural Products 1998 June. Diamond WJ, et al . An alternative medicine definitive guide to cancer. Cancer Conference 12 th Asia Pacific, p.59.