Chaga Mushroom: What It Is, Taste, Evidence and Safety

Chaga (Inonotus obliquus) is a fungus that grows on birch trees in cold climates. It looks like a lump of burnt charcoal on the trunk, and in Russia and Northern Europe it has been brewed as a folk tea for a long time. Today it is sold as a powder, tea and in mushroom coffees. The research is almost all in cells and animals, and there are case reports of kidney damage from heavy use, so it is worth knowing the facts before you take a lot of it.

What is chaga?

Chaga is not a soft mushroom with a cap. The part that is harvested is a hard, black growth on birch bark, called a conk, made of the fungus and wood from the tree. It is broken into chunks or ground into powder and steeped in hot water.

What does chaga taste like?

Chaga tastes mild, woody and slightly bitter, closer to a weak black tea than to mushrooms. Some people pick up a faint vanilla note. It brews dark brown, which is why it is sometimes called a coffee substitute, but it contains no caffeine of its own.

The longer it steeps, the darker and more bitter it gets. Most people drink it plain, with honey, or with milk like a tea. In a mushroom coffee the coffee flavour leads and chaga is barely noticeable.

What does the research show?

In lab and animal studies, chaga extracts have shown antioxidant, anti-inflammatory and blood-sugar-lowering effects, and its compounds have been tested against cancer cells. Memorial Sloan Kettering Cancer Center lists these as preclinical findings. There are no good clinical trials showing a benefit in people, and no health claims are authorised for chaga in the UK.

Chaga safety: the kidney warning

Chaga is very high in oxalate. Memorial Sloan Kettering reports cases of oxalate kidney damage in people who took large amounts of chaga powder every day for months, for example 4 to 5 teaspoons a day for six months, some needing dialysis. These were heavy, long-term doses, far above the amount in a cup of mushroom coffee, but they are a reason not to take high-dose chaga powder daily.

• Avoid high-dose chaga if you have kidney disease or a history of kidney stones.
• Ask your doctor if you take blood thinners such as warfarin: chaga may increase bleeding risk.
• Ask your doctor if you take diabetes medicine: chaga may lower blood sugar further.
• Pregnant or breastfeeding: not enough safety data.

How to take chaga

• Tea: simmer small chunks or a teaspoon of powder for 10 to 20 minutes and strain.
• In coffee: a modest amount as part of a blend. Mataye Mushroom Coffee has 700 mg of chaga fruiting body per cup, with lion's mane, reishi, cordyceps and shiitake.

Read our full mushroom coffee guide, or compare with reishi and cordyceps, and what the evidence says overall in mushroom coffee benefits.

Chaga and the kidneys: case reports

Chaga can be very high in oxalate. A 69-year-old man who took 10 to 15 g of chaga powder a day (with 500 mg of vitamin C) for 3 months developed acute kidney injury with oxalate deposits and recovered after treatment (Kwon et al., 2022). A 49-year-old man who had taken chaga long-term reached end-stage kidney disease; his chaga contained 14.2 g of oxalate per 100 g (Lee et al., 2020). A Mataye serving has 700 mg of chaga. If you have kidney disease or kidney stones, ask your doctor first. More in mushroom coffee side effects.

Sources

• Kwon O et al. (2022). Chaga mushroom-induced oxalate nephropathy that clinically manifested as nephrotic syndrome: a case report. Medicine (Baltimore) 101(10):e28997. PubMed 35451393
• Lee S et al. (2020). Development of end stage renal disease after long-term ingestion of Chaga mushroom. Journal of Korean Medical Science 35(19):e122. PubMed 32419395
• Memorial Sloan Kettering Cancer Center, About Herbs: chaga mushroom