Chaga: what is in the extract?

Chaga doesn't look like a mushroom. It looks like a lump of charcoal stuck to a birch tree, which is oddly close to how it grows. Now it turns up as capsules, powders and tea, so it's fair to wonder what you'd actually be stirring into your mug. Here's what chaga is, what's known about its contents, and the one safety issue that already has real case reports behind it.

Chaga in four lines: a curious fungus, thin human research, one real warning

• What it is: Inonotus obliquus, a fungus whose black outer growth is harvested and turned into powders, extracts and teas.
• What's in it: polysaccharides, triterpenoids, phenolic compounds and melanin, mostly studied in the lab and in animals.
• What's been tested in people: we found no randomised human trial, and a cancer-centre patient page last updated in February 2023 says safety and efficacy haven't been evaluated in clinical studies.
• The warning: oxalate. Chaga powder can be very high in it, and there are published case reports of kidney damage in people who took it for months or years.

A black lump on a birch: what chaga is

Chaga is a wood-rot fungus found mainly on birch in cold climates (Memorial Sloan Kettering). The part people harvest isn't a typical mushroom with a cap and stem. A review in the Journal of Traditional and Complementary Medicine (Szychowski et al., 2021) describes the growth as a sclerotium: a lumpy, cracked, black-brown mass that forms a few years after the fungus enters a living tree, with a dense rust-brown, yellow-veined interior of mycelium. It grows slowly, reaching more than 10 cm across after 10 to 15 years. The sexual fruiting bodies only appear under the bark after the host tree has died, and they are rarely seen. Another review (Camilleri et al., 2024, Heliyon) calls the outer growth a "sterile conk" and notes that its precise function is still unknown.

So when a label says "chaga mushroom", it almost always means this sterile conk. Its chemistry, and the way it's processed, decides what ends up in your cup or capsule.

Chaga has a long folk-medicine history in Siberia and Eastern Europe. Szychowski and colleagues report it was used in Eastern Europe from the 12th century. That's a traditional-use story, not a clinical finding.

What's inside the conk?

Reviews group chaga's compounds into a few families (Camilleri et al., 2024; Szychowski et al., 2021):

• Group: Polysaccharides and glucans; Examples named in the reviews: Not a single compound; a family; What the reviews say about them: Described as the largest group of active compounds besides phenols
• Group: Triterpenoids and related; Examples named in the reviews: Inotodiol, lanosterol, betulin, betulinic acid, trametenolic acid; What the reviews say about them: Reported mainly in laboratory studies
• Group: Phenolics; Examples named in the reviews: Caffeic acid and others; What the reviews say about them: Linked to antioxidant activity in lab tests
• Group: Melanin; Examples named in the reviews: A pigment; What the reviews say about them: Studied for antioxidant activity
• Group: Oxalate; Examples named in the reviews: Oxalic acid and its salts; What the reviews say about them: Raised as a safety issue; see below

Two things help when you read a product page. Composition changes with where the chaga grew, how it was harvested and how it was processed, as Camilleri and colleagues point out, so two products both labelled "chaga extract" can differ. And a compound being present isn't the same as it doing something in your body: the reviews list laboratory activities (antioxidant, anti-inflammatory, effects on cancer cell lines, blood-sugar effects in animals), and Szychowski et al. note that in vivo testing of its anti-cancer effects is very limited. Those are leads for researchers, not results to expect from a capsule.

What have people actually tested it on?

Not much, so far. We didn't find a randomised human trial of chaga in the biomedical databases, and Memorial Sloan Kettering's patient page (updated 20 February 2023) says safety and efficacy haven't been evaluated in clinical studies. The evidence for chaga's health reputation is mainly laboratory and animal work, plus a handful of safety case reports.

That's a perfectly normal place for an interesting ingredient to be early on. It simply means that a product-page line about immunity, energy, ageing or blood sugar has no human trial behind it that we know of.

The part to read twice: oxalate and your kidneys

If you're thinking of taking chaga every day, this is the section that matters.

Oxalate is a natural compound found in many plant foods. In large amounts it can form calcium oxalate crystals in the kidneys, a condition called oxalate nephropathy.

• Japan, 2014. A 72-year-old woman with a history of liver cancer took chaga powder (4 to 5 teaspoons a day) for about six months, then needed haemodialysis. Her kidney biopsy showed oxalate crystals (Kikuchi et al., Clinical Nephrology). The authors presented it as the first reported case.
• South Korea, 2020. A 49-year-old man reached end-stage kidney disease after taking chaga powder for atopic dermatitis: 3 g a day for four years, then 9 g a day for one year. His biopsy showed calcium oxalate crystals. The team measured the leftover powder at 14.2 g oxalate per 100 g, and two other companies' powders at 2.8 and 11.2 g per 100 g, so content differs a lot between products (Lee et al., Journal of Korean Medical Science). The authors estimated his daily oxalate intake from chaga at 420 to 1,260 mg, compared with 200 to 300 mg a day in a typical diet.
• A third case. Memorial Sloan Kettering's page also lists a 69-year-old man who took chaga powder (10 to 15 g a day) plus 500 mg a day of vitamin C for three months. His kidney function improved after haemodialysis and high-dose steroids. Vitamin C also raises oxalate, so that case is muddier.
• Rats, 2026. A Korean research group fed rats chaga powder at doses scaled from the 2020 case, on a calcium-free diet designed to maximise oxalate absorption. After 16 weeks the high-dose group had oxalate crystals, kidney tubule damage and more protein in the urine, although the structural injury was mild (Lee et al., 2026, Journal of Korean Medical Science). It supports the idea that the oxalate matters; it doesn't tell us what happens at a typical supplement dose in a person.

Case reports can't tell us how often this happens: three published cases could mean three in a million or three in a hundred. What they do show is a plausible mechanism, a large difference in oxalate content between powders, and serious outcomes for the people affected. The Lee 2020 authors also point out that oxalate-containing foods raise blood oxalate more when they aren't boiled or brewed, which is why the form of chaga matters (more on that below).

We found no measured oxalate figures for hot-water extracts or teas. The 2026 rat study states that oxalate was the only organic acid detected in chaga extracts in the studies it cites, so don't assume "extract" means "oxalate-free".

If you have kidney disease or a history of kidney stones, or you plan to take chaga daily, please speak to your doctor or pharmacist first. That's our editorial caution, not a threshold from a study.

Medicines. Memorial Sloan Kettering lists two interaction concerns based on laboratory work: a chaga extract inhibited platelet aggregation in a mouse model, which might add to the effect of blood thinners, and chaga showed additive blood-sugar-lowering effects in vitro, which might matter for people on diabetes medicines. Neither has been shown in a human trial, so treat them as questions for a pharmacist. Our guide to supplement and drug interactions suggests how.

Powder, extract or tea: what changes in the cup?

• Form: Powder; What it means: Ground conk; Questions worth asking: Oxalate was measured in powders in the case reports; contents varied from 2.8 to 14.2 g per 100 g in the three samples measured. Ask how much a serving contains and whether oxalate is tested
• Form: Extract; What it means: A concentrate, often made with hot water (some use alcohol or other steps); Questions worth asking: Which extraction method, what the extract ratio is, and whether the figure on the pack is extract weight or raw conk weight
• Form: Tea or blends; What it means: Chips or tea bags, or chaga mixed into coffee or other products; Questions worth asking: How much chaga each serving contains, which is often not stated. No published oxalate figures for tea turned up

A made-up label shows the puzzle. "Chaga extract 500 mg" might be a concentrate made from a much larger weight of conk, or it might be 500 mg of ground powder. Same number, two different products, so the label needs to say which. Our guide to reading supplement labels shows how to check.

Netherlands and EU position, read 8 October 2026

Rules change, so check the current position before relying on this.

• Dutch herbal rules. The Warenwetbesluit Kruidenpreparaten bans certain plants and fungi listed in its annex. Inonotus is not named in the annex (consolidated text on wetten.overheid.nl, in force since 1 July 2022, read 8 October 2026); that is not an authorisation.
• EU novel food rules. A consultation document on the European Commission's site, handled by the Finnish Food Authority, concludes that an extract powder from the chaga conk (made with hot-water extraction plus ultrasound) is "not novel in food supplements". It cites the Novel Food Status Catalogue as saying chaga was used in food supplements before 15 May 1997, and says this applies to powder and extract forms (consultation document). The document is undated and speaks only about food supplements, so check the current catalogue entry, and the rules for foods and drinks, before relying on it.

If chaga caught your eye

Chaga is a fascinating organism with an unproven benefit list and one specific safety issue worth taking seriously. A handful of questions make a product page easier to read: what form is it, how much does a serving contain, is the oxalate content stated, and does anything in your health or medicines (kidneys, blood thinners, diabetes medicines) mean you should ask first?

For the basics of choosing and reading supplements, start with Smart Supplements 101. If you came looking for something calming rather than a mushroom, our sleep hygiene guide is a good next stop.

Where to read next

Chaga has company in the functional mushroom aisle:

• Functional mushrooms and adaptogens: guide hub, for the six popular ingredients, each with its own guide, and a place to start.
• Reishi and sleep: what the research shows, for reishi's calming reputation set against the evidence.
• Lion's mane: the mushroom behind the focus claims, for why fruiting body, mycelium and extract labels matter.
• Cordyceps: fungus, formulations and performance claims, for which species the endurance trials used and the Dutch position as read on 8 October 2026.

Written by Smart Supplements with AI assistance from the sources linked in the text. It has not been reviewed by a clinician.

Last updated: 12 October 2026

This article is for informational purposes only and is not intended as medical advice. Always consult a healthcare professional before starting any new supplement, especially if you take prescription medication.