Chaga Mushroom: Benefits, Side Effects and Who Should Avoid It

What is chaga?

Chaga (Inonotus obliquus) is a fungus that grows mainly on birch trees in cold northern regions, including Russia, Scandinavia, Canada and Scotland. It looks like a lump of burnt charcoal on the outside, with a rusty orange-brown core. It has been used in Russian and Siberian folk medicine for centuries, usually simmered into a tea with a mild, earthy, slightly vanilla taste. Today it’s sold as chunks, powders, extracts, capsules and in mushroom coffee.

The part people harvest isn’t a mushroom cap. It’s a canker (sometimes called a conk or sclerotium): a hard mass of fungal tissue that pushes out through the bark of a living birch. It’s a sterile growth: the fungus spreads its spores later on, so cutting the canker takes it before it has reproduced. That matters for sustainability, which we come back to below.

Chaga grows slowly. Future Woodlands Scotland describes a sterile conk forming roughly every 5 to 7 years over a period of 20 to 80 years, which is one reason wild stocks can’t keep up with fast-rising demand.

What’s in chaga?

Researchers have mainly looked at four groups of compounds in chaga:

• Polysaccharides, including beta-glucans. A 2025 laboratory comparison measured about 5.7% to 11.9% beta-glucans in whole wild chaga samples.
• Triterpenoids, such as inotodiol and trametenolic acid, which the same study used as markers of genuine chaga.
• Phenolic compounds, which account for much of chaga’s antioxidant activity in lab tests, and melanin, the dark pigment in the burnt-looking outer crust.
• Oxalate. This is the one to know about. Korean doctors measured 2.8g to 14.2g of oxalate per 100g in three commercial chaga powders. A typical diet contains about 200mg to 300mg of oxalate a day.

You’ll often read that chaga is rich in betulin, a compound from birch bark. In the 2025 analysis, betulin and betulinic acid weren’t detected in any of the samples tested, so treat that selling point with some caution.

Chaga benefits: what the research shows

Mushrooms, chaga included, have no authorised health claims in Great Britain. Here is what scientists have actually studied, and how much weight each type of study can bear.

In short, chaga is an interesting subject for laboratory research, but its effects in people haven’t been demonstrated. If you see a product promising immune, blood sugar or cancer benefits, that’s a red flag rather than a selling point. For how the wider group of woody mushrooms compares, see our guide to mushrooms and inflammation research.

Chaga side effects and your kidneys

Why oxalate matters

Oxalate binds to calcium and can form crystals. Most of us handle the 200mg to 300mg in an ordinary daily diet without trouble, but very large amounts can build up as calcium oxalate crystals inside the kidneys, a condition called oxalate nephropathy. With chaga powders measured at up to 14.2g of oxalate per 100g, a few grams a day adds up quickly: the doctors in one case worked out that 3g to 9g of powder a day supplied roughly 420mg to 1,260mg of oxalate, two to five times a typical diet.

The case reports

• Japan, 2014: a 72-year-old woman took 4 to 5 teaspoons of chaga powder a day for 6 months. Her kidney function fell, oxalate crystals were found on biopsy and she needed dialysis. It was the first published case linking chaga to oxalate kidney damage.
• Korea, 2020: a 49-year-old man took chaga powder for 5 years (3g a day for 4 years, then 9g a day for a year) and developed end-stage kidney disease.
• Korea, 2022: a 69-year-old man took 10g to 15g of chaga powder a day, plus 500mg of vitamin C, for 3 months. He developed acute kidney injury and needed dialysis and high-dose steroids; his kidney function recovered after about a month.

Case reports can’t tell us how common this is, and all three involved daily spoonfuls of powder for months, not an occasional cup of tea. But they’re serious enough that with chaga, the kidney question comes first. High-dose vitamin C is itself a recognised cause of oxalate kidney damage, which is why the 2022 case mentions it, so it’s wise not to pair chaga with high-dose vitamin C supplements.

Other side effects

• Bleeding: chaga may slow blood clotting, which matters if you take blood thinners or are having surgery.
• Low blood sugar: it may add to the effect of diabetes medicines.
• Digestive upset and, rarely, allergic reactions, as with any mushroom.

To help prevent kidney stones in general, the NHS advises adults to drink 2.5 to 3 litres of water a day and to make sure they get enough calcium, but not to change their diet without speaking to a doctor first.

Medicines and who should avoid chaga

Chaga hasn’t been clinically tested, so these precautions come from lab findings, case reports and drug-interaction monographs:

• Kidney disease or a history of kidney stones: avoid chaga, because of its oxalate content.
• Blood thinners and bleeding disorders: Memorial Sloan Kettering warns that chaga may increase bleeding risk if you take warfarin, and interaction monographs list aspirin and heparin too. Don’t use chaga if you have a bleeding disorder.
• Diabetes medicines: taking chaga alongside insulin or tablets that lower blood sugar might push your blood sugar too low.
• Autoimmune conditions and immunosuppressants: because chaga might make the immune system more active, it’s best avoided if you have a condition such as lupus, multiple sclerosis or rheumatoid arthritis, or if you take immunosuppressants such as ciclosporin, tacrolimus or steroid tablets, including after a transplant.
• Surgery: stop at least 2 weeks before a planned operation, because of the possible effects on bleeding and blood sugar.
• Pregnancy and breastfeeding: not enough is known about chaga’s safety, so avoid it. We don’t recommend our products during pregnancy or breastfeeding.
• Children: there’s no safety research, so we wouldn’t give chaga to children.

iIf you take any regular medicine, check with your GP or pharmacist before trying chaga, and tell them if you already use it.

Is chaga safe every day? How much is too much?

There’s no official safe daily amount of chaga in the UK, and no clinical trials to set one. The kidney case reports involved 3g to 15g of powder a day for months or years: amounts to stay well clear of. Oxalate content also varied five-fold between the brands tested, so one company’s serving isn’t the same as another’s.

A sensible approach, if you’re healthy and want to try it:

• Keep it occasional, rather than several cups or spoonfuls every day.
• Don’t stack it: chaga tea plus a chaga capsule plus a chaga coffee blend soon adds up.
• Drink plenty of water, and stop and speak to your GP if you feel unwell.

How to make chaga tea

Chaga is too hard to eat, so it’s brewed with a long, gentle simmer rather than a quick steep.

From chunks

1. Put 2 or 3 small chunks (about the size of a sugar cube) in a pan with roughly a litre of water.
2. Bring it up to a gentle simmer, then keep it just below boiling for 30 to 60 minutes. Larger chunks need longer.
3. Strain. The tea should be a dark, reddish-brown colour, a bit like black coffee.
4. Dry the chunks and reuse them once or twice, until the tea comes out pale.

From powder

Fine powder brews faster. Simmer a small amount in a pan of water for 10 to 15 minutes, then strain through a fine sieve or coffee filter. Be wary of stirring spoonfuls of raw powder straight into drinks every day: all three kidney case reports involved people taking large amounts of powder.

How it tastes

Chaga tea is mild, earthy and slightly vanilla-like, often compared with weak coffee. A slice of fresh ginger or a stick of cinnamon in the pan works well. It contains no caffeine on its own. For a broader guide to brewing reishi, lion’s mane and other mushrooms, see how to make mushroom tea, and if you prefer your mushrooms in a mug of coffee, our mushroom coffee guide covers the caffeine and side effects.

Chaga vs reishi and other mushrooms

Chaga and reishi are the two woody mushrooms people most often weigh up. Neither has an authorised health claim, and they have different safety notes: chaga’s is oxalate and the kidneys, while reishi has rare case reports of liver injury. Rather than repeat it here, our reishi guide has a side-by-side table of reishi vs chaga vs turkey tail covering what each is, how it’s taken, what’s been studied and the safety notes.

For the other popular mushrooms, see our guides to turkey tail, lion’s mane and cordyceps, or the quick comparison of lion’s mane vs reishi vs cordyceps. Our functional mushrooms UK guide puts them all side by side.

We don’t sell chaga. Our own mushroom product is a reishi hot chocolate, made with cocoa, reishi mushroom, maca, cinnamon and coconut sugar. It’s for adults, and the cacao contains a little natural caffeine, so it isn’t caffeine-free. If an evening mug appeals, you can read more about it in our reishi cacao guide or reishi and sleep.

The FSA’s 10mg a day figure for CBD is precautionary advice rather than a legal limit, set while longer-term safety research continues. At Evopure we think it is a very cautious figure, and many adults use more. If you go above it, increase slowly, and check with your GP or pharmacist first if you take any medication.

Wild chaga, sustainability and the UK

Almost all chaga on sale is harvested from the wild. A 2020 conservation paper, co-written by a University of Stirling researcher, called chaga “a medical marvel but a conservation dilemma”. Because the canker is cut away before the fungus has had a chance to reproduce, the authors see the harvest as a serious conservation concern and called for urgent education and legal protection.

Does chaga grow in the UK? Yes. It grows on birch here, mostly in Scotland. In late 2024 Future Woodlands Scotland funded an Edinburgh co-operative to research whether chaga could be cultivated on Scottish birch instead of being picked from the wild.

If you’re tempted to forage it yourself:

• Always get the landowner’s permission first.
• Take only a little, and leave plenty behind.
• Be sure of your identification: burnt wood, burrs and other fungi on birch can look similar to an untrained eye.

Mycelium products are not the same thing

Some “chaga” powders aren’t made from the canker at all, but from chaga mycelium (the root-like threads) grown on rice, oats or sorghum, with the grain left in. A 2025 laboratory comparison found these fermented grain products were 33% to 68% starch (alpha-glucans), compared with less than 2% in genuine chaga, had lower beta-glucan levels, and lacked chaga’s marker triterpenoids. The authors work for a company that sells chaga canker supplements, so they have an interest in the result, but the starch finding fits the wider picture covered in our guide to choosing the best mushroom supplement in the UK.

How to choose a chaga product

If you decide to try chaga, check these:

• Check what it’s made from. Look for “chaga canker” or “sclerotium” on the label. “Mycelium”, “myceliated grain” or “full spectrum” with rice or oats in the ingredients means you’re buying a lot of starch.
• Look for a measured beta-glucan figure and ask which test method was used. A beta-glucan figure is more useful than a vague “polysaccharides” percentage, which can include starch.
• Ask for test certificates for heavy metals and microbes. Good suppliers will share them, and it’s worth asking whether they test oxalate.
• Ask where and how it was harvested, or whether it’s cultivated.
• Avoid disease claims. Foods and supplements in the UK aren’t allowed to claim they treat or prevent any disease, so a seller promising that chaga treats cancer, diabetes or anything else isn’t following the rules.
• Watch the serving size. Several grams of powder a day is in the range seen in the kidney case reports.

Gummies are another popular format; our mushroom gummies guide explains how much mushroom and sugar a typical gummy contains.

Related guides

• If you’d rather eat your mushrooms, see our guide to maitake mushroom, nutrition and how to cook it.
• Chaga often turns up in menopause blends; see the best mushroom supplements for menopause and what to check before you buy.
• What’s in Spacegoods, a mushroom drink that lists chaga in every scoop.
• Chaga also appears in mushroom coffees such as Four Sigmatic’s Shield instant coffee.
• Chaga is one of five extracts in Mico-Five; see our Hifas da Terra guide.
• Chaga is also one of the 10 mushrooms in Ankhway mushroom gummies.
• Chaga also turns up in drink blends, such as Ancient and Brave Cacao + Chaga (1.5g per 10g serving), so add up your total if you use more than one.
• For a mushroom you can cook with, see our guide to shiitake benefits, side effects and how to eat them.