Hymenochaetaceae
Inonotus obliquus
Chaga · Birch conk
- Kingdom
- Fungi — not a plant
- Part used
- whole
- Native range
- Birch forest across the circumboreal north — Siberia, northern Europe, Canada
- Morphology
- Not a mushroom but a sterile canker: a hard black cracked mass, like burnt charcoal, protruding from the trunk of a living birch, with a rusty orange interior.
What is in it
Evidence
No adequate controlled human evidence. Laboratory and animal work on betulinic acid is extensive and has not been tested clinically for this preparation.
Safety
Extremely high oxalate content. Documented cases of oxalate nephropathy and irreversible kidney failure from regular chaga consumption, including a well-reported Japanese case requiring dialysis. Contraindicated in kidney disease, in stone formers, and alongside anything else raising oxalate load. Antiplatelet activity is reported.
Interactions: Additive bleeding risk with anticoagulants; May lower blood glucose
Regulatory: Permitted as a listed ingredient. Several poison centres have issued oxalate warnings.
Historical use
Used across Siberia, Russia and the Baltic as a tea and folk remedy, and known in Khanty and other northern practice. Its wider reputation owes a great deal to Solzhenitsyn’s Cancer Ward, in which a doctor treats peasants with birch fungus.
Recorded as history and attributed where possible. Long use establishes that a plant was widely used, not that it worked, and not that it was safe.
Worth knowing
Chaga is the entry where a plausible-sounding "just a tea" preparation has taken kidneys.
Its oxalate content is among the highest of anything consumed regularly, and the case reports are specific: people drinking chaga tea daily for months presenting with oxalate nephropathy, some requiring dialysis, with the damage irreversible. It is not an idiosyncratic reaction; it is a predictable consequence of a very high oxalate load.
It also draws most of its cancer reputation from a novel. Solzhenitsyn's Cancer Ward describes a country doctor treating peasants with birch fungus, and that fictional passage has done more for chaga's market than any study. The betulinic acid work is real laboratory science and has never been tested in a person for this purpose.
Harvesting also kills slowly: the conk takes many years to form and taking it damages the host birch.
Nomenclature verified against GBIF backbone taxonomy.