Chaga: the birch mushroom from northern forests

Chaga is the common name for Inonotus obliquus, a fungus that lives on birch trees in the colder parts of the northern hemisphere. You will also see it called cinder conk, clinker polypore, birch canker polypore, black mass or, in Chinese, bai hua rong. The word chaga came into Russian from Komi, a language spoken west of the Urals, where it simply means mushroom.

It looks like a lump of burnt charcoal stuck to a tree. The crust is black, hard and cracked, coloured by melanin, the same pigment found in human skin and hair. Inside, it is a soft, rusty orange with a corky feel.

Strictly speaking, what people harvest is not a mushroom. It is a sterile conk, or sclerotium: a dense mass of fungal threads packed in with wood. The spore-bearing fruiting body only forms under the bark once the tree or part of it has died, and few people ever see one.

Chaga usually enters a birch through a wound such as a snapped branch, then rots the heartwood for decades. An infected tree can live on for 30 to 80 years. Most conks are 10 to 25 cm across, and on old trees they can pass 50 cm.

Birch is the usual host, though alder, beech and poplar have been recorded too. Chaga is most common in Russia, Scandinavia, the Baltic states, Korea, northern China, Canada and the northern United States. In Britain it has been found mainly on birch in Scotland, and it is uncommon.

Written records of chaga as a folk remedy go back to the sixteenth century in Siberia and Russia. Russian collections of folk medicine describe it being used for stomach complaints, liver problems, tuberculosis and intestinal worms. In northern and central Russia it was made into tinctures. All of this is traditional use. It tells us how people used chaga, and says nothing about whether it worked.

The everyday use was as a drink. Dried chunks were grated to a coarse powder and brewed or simmered into a dark, earthy tea, and in some places it stood in for coffee when coffee was hard to get. Chaga tea is still widely drunk in Russia and Korea.

Some uses had nothing to do with health. The Potawatomi people of North America call the fungus shkitagen and use it as tinder for keeping fire, because an ember dropped into it smoulders slowly for a long time.

Chaga also turns up in fiction. In the decades after, Soviet doctors published a handful of small reports on chaga preparations, which we look at in the evidence section below.

Scientists have isolated dozens of compounds from chaga. The ones studied most fall into a few groups:

• Polysaccharides, long chains of sugars including beta-glucans, which make up about a third of some purified extracts. Oats, barley and most edible mushrooms contain beta-glucans too.
• Triterpenoids such as inotodiol, lanosterol, trametenolic acid, ergosterol, betulin and betulinic acid. Betulin is what makes birch bark white, and its presence in chaga is usually put down to the host tree.
• Phenolic compounds such as protocatechuic, gallic, caffeic and syringic acids, plus yellow pigments called styrylpyrones and lignin fragments from the wood.
• Melanin, the dark pigment in the crust.
• Oxalate. Chaga has one of the highest oxalate levels recorded in any living thing, reported at 2,800 to 11,200 mg per 100 g of dried conk. We come back to this in the safety section.

Nutrition data is scarce. Chaga is very low in calories and high in fibre, but reliable vitamin and mineral figures are hard to find.

The mix also shifts with the tree, the region, the age of the conk and the extraction method. Hot water pulls out polysaccharides well, and alcohol is better at drawing out triterpenoids, so two chaga products can contain quite different things.

Most articles about chaga mushroom benefits draw on the same research, and nearly all of it was done on cells in a dish or on mice and rats. Here is what it reported.

• Antioxidant activity. In a 2007 study from Niigata in Japan, Nakajima and colleagues compared hot water extracts of four medicinal fungi. Chaga scavenged superoxide and hydroxyl radicals most strongly of the four in the test tube. The team isolated seven small phenolic compounds behind that activity, one of them new to science.
• Inflammation and immune signalling. In mouse immune cells, chaga extracts lowered nitric oxide and signalling molecules such as TNF-alpha, IL-6 and IL-1 beta, and some compounds blocked the enzymes iNOS and COX-2. Studies on the polysaccharides found some immune signals rose while others fell, depending on the model.
• Blood sugar. In diabetic mice, chaga extracts lowered blood glucose and insulin resistance, and one widely quoted study reported a 31% fall over three weeks. In the test tube, some compounds blocked alpha-glucosidase, a starch-digesting enzyme, more strongly than the diabetes drug acarbose.
• Cholesterol and weight. In an eight week rat study, chaga extract lowered LDL cholesterol, total cholesterol and triglycerides. Mice on high fat diets given chaga polysaccharides gained less weight and showed shifts in their gut bacteria.
• Viruses and bacteria. Water extracts acted against hepatitis C, herpes simplex, HIV and SARS-CoV-2 in cell cultures, and slowed several bacteria, with Staphylococcus aureus the most sensitive.
• Fatigue. Mice given chaga polysaccharides swam for longer before exhaustion and had lower blood lactate.

Other animal studies have reported effects on pain, allergy, memory, liver and kidney damage, and blood clotting. The clotting finding comes up again in the safety section.

A 2024 review in the journal Mycology by Ern and colleagues gathers most of this work in one place. Its authors write that the mechanisms are still poorly understood, and that nobody yet knows whether chaga compounds behave the same way when eaten as food.

There are no modern, placebo-controlled trials of chaga in people. Leading herb safety databases state that chaga's safety and effectiveness have yet to be evaluated in clinical studies. Any fair reading of the evidence has to start there.

The nearest thing to human data comes from the Soviet Union. A 2024 review by Tee and colleagues lists two old reports:

• Dosychev and Bystrova described 50 people with psoriasis who took a chaga preparation, one tablespoon three times a day before meals. They reported that skin eruptions cleared in most of them and that digestive symptoms eased.
• Fedotov described 58 people with peptic ulcers given one of three daily doses of a chaga preparation. Pain eased for a while, and more so at the higher doses.

Neither report had a placebo group, both were published in Russian decades ago, and neither can be checked against modern trial standards.

What the research does show:

• Chaga contains compounds with measurable antioxidant and anti-inflammatory activity in lab tests.
• Very high intake over months has been linked to serious kidney damage in several people.

What it does not show:

• That results in mice carry over to a mug of tea or a supplement. Many studies used concentrated fractions or high doses per kilo of body weight.
• That antioxidant activity in a test tube happens inside the body. Plenty of compounds that look strong in a dish are poorly absorbed.
• What a safe or useful daily amount would be.

One question nobody has answered yet is how much of chaga's oxalate ends up in a concentrated extract compared with the raw powder in the case reports below. We could not find a published study that measured it.

Tea is the traditional way to take chaga and still the most popular. It tastes earthy and a little bitter, with a soft vanilla note, and it has no caffeine. There are two usual methods:

1. Chunks. Break dried chaga into sugar-cube-sized pieces and simmer a few in water, just below the boil, for 30 minutes to a few hours. The liquid turns as dark as black coffee. Many people reuse the chunks two or three times.
2. Powder or tea bags. Pour just-boiled water over ground chaga, leave it for five to ten minutes, then strain.

A 2022 lab study from the University of Maine by Alhallaf and Perkins compared ways of extracting chaga. Powder steeped for six minutes at 100°C was among the most active extracts against inflammatory markers in mouse immune cells, level with an optimised ethanol and water extract. It was a cell study, so it is a guide to brewing method only.

Honey, cinnamon and milk are common additions. Chaga also turns up in mushroom coffee, often blended with Lion's Mane or Cordyceps. Because of the oxalate, strong chaga tea is not something to drink by the pint for months on end.

You can buy chaga in more forms than most mushrooms:

• Raw chunks for simmering into tea
• Ground powder, loose or in tea bags
• Hot water extracts, sold as powders or in capsules
• Dual extracts, made with hot water and then alcohol to pull out both polysaccharides and triterpenoids
• Tinctures, which are alcohol-based liquids taken by the dropper
• Capsules, tablets and gummies, often in blends with other mushrooms

Supplements are usually far more concentrated than a weak tea, so the label matters. Things worth checking before you buy:

• Which part of the fungus is in it. Wild chaga is the sclerotium from the tree. Some products use mycelium grown in a lab, often on grain. Chaga grown on artificial media makes a different set of compounds, with fewer phytosterols such as lanosterol, and mycelium on grain can end up mostly grain starch. Cultivation does take pressure off wild chaga, so it is a trade-off.
• The extract ratio. A 10:1 extract means roughly 10 kg of raw chaga went into 1 kg of extract. Ratios are not standardised, so a beta-glucan percentage is more useful for comparing brands.
• Testing. Fungi can take up heavy metals, and a reputable brand will share its heavy metal and microbial test results if you ask.
• Where it came from. Wild supplies have been heavily depleted. Careful harvesters take part of a conk in late winter, when the tree is dormant, and leave the rest to regrow.

A very cheap tub that does not say how much extract is in each serving probably contains a lot of filler.

In the small amounts in tea and most supplements, chaga seems to be well tolerated, though no large studies have looked at side effects. The concerns come from case reports, animal research and what chaga contains.

The clearest one is the kidneys. Too much absorbed oxalate can form calcium oxalate crystals that damage kidney tissue, and three case reports describe this after heavy chaga use:

• In 2020, Lee and colleagues in Korea reported a 49-year-old man who had taken chaga powder for years for severe eczema and developed end-stage kidney disease. His leftover chaga tested extremely high in oxalate.
• In 2022, Kwon and colleagues in Korea reported a 69-year-old man who took 10 to 15 g of chaga powder plus 500 mg of vitamin C a day for three months. He developed acute kidney injury and recovered after dialysis and steroids.

These are single cases with large amounts, so they cannot tell us how common the problem is.

Speak to your GP or pharmacist before taking chaga if:

• You have kidney disease or have had kidney stones. Calcium oxalate stones are the most common type.
• You take a blood thinner or antiplatelet medicine such as warfarin, apixaban, clopidogrel or daily aspirin. In 2006, Hyun and colleagues isolated a peptide from chaga that stopped platelets clumping in the lab and in mice. Whether that raises bleeding risk in people is unknown.
• You take insulin or diabetes tablets, as chaga lowered blood sugar in animals and could add to their effect.
• You have surgery coming up. Tell your surgical team, as doctors commonly advise stopping herbal products about two weeks beforehand.
• You have an autoimmune condition such as rheumatoid arthritis, lupus or multiple sclerosis, or take immune-suppressing medicine.
• You are pregnant or breastfeeding. There is no safety research, so the usual advice is to avoid it.
• You take high-dose vitamin C, which the body partly turns into oxalate.

Chaga is not suitable for children unless a doctor advises it. You can report a suspected side effect from any herbal product to the MHRA through the Yellow Card scheme.

There is no established safe or effective dose of chaga, because the human studies needed to set one have not been done. Neither the NHS nor the Food Standards Agency publishes a recommended amount.

What we do know comes from the other direction. The people in the kidney case reports were taking large amounts, such as 4 to 5 teaspoons of powder or 10 to 15 g a day, for months or years. That is many times what a typical supplement provides.

Some sensible habits:

• Stick to the amount on the label and do not stack several chaga products.
• Keep chaga tea to a cup or so a day, and drink plenty of water.
• Stop and see your GP if you notice changes in how often you pass urine, swollen legs or unusual tiredness.

In the UK, chaga is sold as a food. That covers loose tea, powders and food supplements such as capsules and gummies. Food supplements in England fall under the Food Supplements (England) Regulations 2003 and general food law, with similar rules in Scotland, Wales and Northern Ireland. They are not licensed medicines and are not checked for effectiveness before sale. The seller is responsible for making sure they are safe and correctly labelled.

Health claims are tightly controlled. The GB nutrition and health claims register lists the claims food businesses are allowed to make, and there is no authorised claim for chaga. Plenty of US websites say these things under different rules. On a UK product, treat those promises as a red flag.

The NHS does not publish guidance on chaga specifically. Its general advice is to tell your GP or pharmacist about any herbal remedies or supplements you take, especially before starting a new medicine or having an operation.

You will find chaga in health food shops, some independent pharmacies, specialist mushroom sellers and online, and increasingly in mushroom coffee on supermarket shelves. If you are tempted to forage it, you need the landowner's permission, it is uncommon in Britain, and cutting into a living tree can harm it.

Chaga is one of six mushrooms in Starshroooms, alongside Lion's Mane, Reishi, Cordyceps, Maitake and Tremella, plus Panax Ginseng. We use a 10:1 chaga extract, concentrated ten times over from the raw material.

The gummies are blackcurrant flavoured, vegan and caffeine free, so you will not taste any of chaga's earthiness. The suggested amount is two gummies a day. The chaga in them is one part of a mixed blend, a much smaller amount than the powder quantities in the kidney case reports above.

A 60 gummy pack lasts a month and costs £24.99, and there is a 10 gummy trial pack for £4.99 if you would like to try the taste first. You can read the studies behind each ingredient on our research page or see the full mushroom gummies range.

The safety advice above applies to our gummies as to any chaga product, so if you take blood thinners or diabetes medicine, have kidney problems, or are pregnant or breastfeeding, check with your GP or pharmacist first. The studies in this guide looked at chaga on its own, in various forms and amounts, and did not test our gummies. Descriptions of traditional use are not health claims.