Reishi

Reishi is a bracket or shelf fungus with a characteristic reddish-brown, varnished, kidney-shaped cap that grows on hardwood trees ^[1]. In China it is called lingzhi, meaning roughly "divine mushroom," and it has been revered in East Asian cultures for over two thousand years ^[1]. Its scientific naming has long been unsettled; specimens have been placed under Ganoderma lucidum, and East Asian cultivated material is now often assigned to closely related species such as Ganoderma lingzhi ^[1].

Reishi has a long history in traditional Chinese and Japanese medicine, in which the dried mushroom is typically sliced or powdered and simmered into a bitter decoction ^[1]. Traditional texts credited it with promoting vitality and longevity, and it became a symbol of good fortune and health in East Asian art and folklore ^[1]. Today it is consumed as teas, powders, and extract-based supplements.

The mushroom's most studied constituents are triterpenoids called ganoderic acids, whose structures resemble steroid hormones, along with polysaccharides that include beta-glucans ^[1][3]. Laboratory research has explored immune-modulating, antioxidant, and anti-inflammatory activities, and reviews have examined possible effects in models of neurodegenerative disease ^[1][3]. In cancer care, a Cochrane systematic review of randomized trials concluded that reishi should not be used as a first-line treatment, but that as an addition to conventional chemotherapy or radiotherapy it might improve tumor response and some measures of immune function, while being generally well tolerated ^[2]. Overall, human evidence remains limited and of variable quality ^[2].

Generally safe with occasional dry mouth, GI upset, or dizziness. It may have mild blood-thinning and blood-pressure-lowering effects, so caution is warranted with anticoagulants and before surgery. Rare liver concerns have been reported with certain powdered products.