The tree fungus known as reishi has a long history of use in China and Japan as a semi-magical healing herb. More revered than ginseng and, up until recently, more rare, many stories tell of people with severe illnesses journeying immense distances to find it. Presently, reishi is artificially cultivated and widely available in stores that sell herb products.

Reishi (like its fungi “cousins” maitake, Coriolus versicolor, and shiitake) is marketed as a kind of cure-all, said to strengthen immunity, help prevent cancer, and also possibly treat cancer as well. It is also said to be useful for autoimmune diseases (such as myasthenia gravis and multiple sclerosis), viral infections, high blood pressure, diabetes, enhancing mental function, altitude sickness, ulcers, andinsomnia. However, while there has been a great deal of basic scientific research into the chemical constituents of reishi, reliable double-blind, placebo-controlled studies are all but nonexistent. (For information on why such studies are essential, seeWhy Does This Database Rely on Double-blind Studies?)

For example test tube studiesindicate that reishi has immunomodulatory effects.1-5 This means that reishi may affect the immune system, but not necessarily that it strengthensit. (Alternative medicine proponents often blur the difference between these two ideas.) However, one, small, double-blind, placebo-controlled human trial failed to find any significant immunomodulatory effects.23Other weak evidence hints that reishi may have chemopreventive properties, suggesting that it may help prevent cancer.4,6-12 However, a great many substances fight cancer in the test tube, while few actually help people with the disease.

Other highly preliminary forms of evidence suggest that reishi may have antiviral effects 13-19and possibly antibacterial effects as well.20 However, it is a long way from studies of this type to meaningful clinical uses.

Contemporary herbalists regard reishi as an adaptogen, a substance believed to be capable of helping the body resist stress of all kinds. (For more information on adaptogens, see the article on Ginseng.) However, there is no meaningful evidence to support this claim.

One questionable double-blind study performed in China reportedly found reishi helpful for neurasthenia. The term neurasthenia is seldom used in modern medicine; it generally indicates fatigue due to psychological causes.22