Medicinal fungi are those fungi which produce medically significant metabolites or can be induced to produce such metabolites using biotechnology. The range of medically active compounds that have been identified include antibiotics, anti-cancer drugs, cholesterol inhibitors, psychotropic drugs, immunosuppressants and even fungicides. Although initial discoveries centred on simple moulds of the type that cause spoilage of food, later work identified useful compounds across a wide range of fungi.
Although fungal products have been used in traditional and folk medicines, probably since pre-history, the ability to identify beneficial properties and then extract the active ingredient started with the discovery of penicillin by Alexander Fleming in 1928. Since that time, many additional antibiotics have been discovered and the potential for fungi to synthesize biologically active molecules useful in a wide range of clinical therapies has been extensively exploited.
Pharmacological research has now isolated antifungal, antiviral, and antiprotozoan, isolates from fungi. Many forms and phyla of fungi including mushrooms, fermentation mold, mycelia, sclerotium, and lichens, have a history of medicinal use spanning millennia. The fungus with probably the longest record of medicinal use, Ganoderma lucidum, is known in Chinese as líng zhī ("spirit plant"), and in Japanese as mannentake ("10,000 year mushroom"). In ancient Japan, Grifola frondosa was worth its weight in silver, although no significant therapeutic benefits have been demonstrated in humans.
Lichens have also been used in many folk medicine traditions to treat a wide range of ailments. Research has demonstrated a range of therapeutically significant compounds in a range of lichen species but none are currently believed to be in use in mainstream medicine.
A number of fungi have well documented psychotropic effects, some of them severe and associated with sometimes acute and life-threatening side-effects. Well known amongst these is Agaricus muscarius, the Fly Agaric. More widely used informally are a range of fungi collectively known as "Magic mushrooms" which contain psilocybin and psilocin.
The history of bread-making is also peppered with references to deadly ergotism caused by Ergot, most commonly Claviceps purpurea, a parasite of cereal crops. A number of therapeutically useful drugs have subsequently been extracted from ergot including ergotamine, Pergolide and Cabergoline.
Aspergillus niger is used to produce recombinant phytase, an enzyme added to animal feeds to improve absorption of phosphorus.
Edible species with medically significant metabolites
Many edible species have been shown to produce medically significant metabolites. However eating fungi with such properties is most unlikely to result in any medically beneficial effect. Most compounds of interest when used for medical purposes are synthesized on an industrial scale and are packaged and administered in ways that maximise the potential benefit.
Those fungi listed below have been shown to have significant effect as evidenced by human clinical trials published in peer reviewed papers and quoted in secondary sources.
Agaricus subrufescens (Agaricus blazei/brasiliensis, almond mushroom) is a fungus associated with Brazil and Japan. Research and small clinical studies demonstrated A. subrufescens extracts have antihyperglycemic and anticancer activities.Brefeldin A and blazein were isolated from A. subrufescens.
Cordyceps sinensis is an entomopathogenic fungi collected on the Tibetan Plateau. The immunosuppressant ciclosporin was originally isolated from Cordyceps subsessilis. The adenosine analog cordycepin was originally isolated from Cordyceps. Other Cordyceps isolates include, cordymin, cordycepsidone, and cordyheptapeptide. CS-4 is commercially sold as C. sinensis, but Cs-4 has recently been confirmed to be a different species from the Cordyceps species used in traditional Chinese medicine. CS-4 is properly known as Paecilomyces hepiali. Hirsutella sinensis is the accepted asexual form of C. sinensis. 
Lentinula edodes (Shiitake) has been used as a source of Lentinan, AHCC, and eritadenine. In 1985 Japan approved lentinan as an adjuvant for gastric cancer. Studies there indicate prolonged survival and improved quality of life when gastric cancer patients with unresectable or recurrent diseases are treated with lentinan in combination with other chemotherapies.
Trametes versicolor (Coriolus versicolor, yun zhi, kawaratake, turkey tail) have produced protein-bound polysaccharides PSK and PSP (polysaccharopeptide) from different mycelia strains. In Japan, PSK is a gastric cancer adjuvant. Japan began using PSK in 1977, while China began using PSP in 1987.
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