Chaga is the common name for Inonotus obliquus, a fungus that grows mainly on birch trees in cold northern climates. What people harvest and sell as “chaga” is not a typical mushroom cap but a hard, black, cracked growth on the trunk called a sterile conk or sclerotium. It has a long history in Russian and Eastern European folk medicine, where it was taken as a tea, and it is now sold as powders, capsules and extracts marketed for immunity, inflammation and “recovery.”
The single most important fact is that there are no modern controlled human trials of chaga. Almost all of the research is in cell culture and animals. The best-documented human finding is a harm: chaga is very high in oxalate, and published case reports link heavy, long-term use to oxalate kidney damage, including one case of permanent kidney failure.
This page summarizes what the published research, case reports and regulators report. It is for education only and is not medical advice.
| Property | Detail |
|---|---|
| Type | Medicinal fungus (Inonotus obliquus); the sterile conk (sclerotium) is used |
| Other names | Cinder conk, birch conk, clinker polypore |
| Forms sold | Tea made from the conk; powders, capsules, tablets and extracts |
| Human dose data | No controlled trials; intakes in kidney-injury case reports were 3–15 g/day of powder |
| Half-life | Not established in humans. One constituent, inotodiol, had an oral half-life of ≈139 min (≈2.3 h) in mice |
| Notable constituent | Oxalate: 2.8–14.2 g per 100 g in three commercial powders tested |
| US status | Sold as a dietary supplement; FDA does not approve supplements before marketing |
| WADA status | Not named on the 2026 Prohibited List |
What it is
Inonotus obliquus is a parasitic fungus that decays the trunks of living trees. Birch is its main host. It infects a tree through wounds in the bark and, a few years later, produces the irregular black-brown growth sold as chaga. The inside of that growth is a dense, rust-brown mass of fungal tissue (mycelium). These growths enlarge slowly, reaching more than 10 cm across after 10–15 years (Szychowski et al., J Tradit Complement Med 2021). Memorial Sloan Kettering (MSK) notes that the conk used medicinally contains wood from the host tree as well as the fungus (MSK About Herbs).
Researchers have isolated several groups of compounds from chaga (Szychowski et al., 2021):
- Triterpenoids, including inotodiol;
- Polysaccharides (complex carbohydrates), studied mainly for effects on immune cells;
- Melanins and other polyphenols;
- Ergosterol and its peroxide, and benzoic acid derivatives.
A chemical analysis of Finnish, Russian and Thai chaga extracts found oxalic acid as the main organic acid in every sample, with the highest amount in an aqueous extract from Russia. Gallic, protocatechuic and p-hydroxybenzoic acids were also present (Glamočlija et al., J Ethnopharmacol 2015). The oxalate content matters for safety (see below).
Chaga sits alongside other “functional” mushrooms in this library, such as reishi, lion’s mane and cordyceps. These are different species with different chemistry and evidence.
How it behaves in the body
There are no pharmacokinetic studies of chaga in humans. Because chaga is a mixture of many compounds, it has no single half-life.
The only formal pharmacokinetic data come from one purified constituent, inotodiol, given to mice (Kim et al., Plants 2021):
| Parameter (mice) | Intravenous, 2 mg/kg | Oral |
|---|---|---|
| Elimination half-life | 49.4 min | 138.6 min |
| Peak plasma level | 2,582 ng/mL | 49.6 ng/mL |
| Time to peak | Not applicable | 40 min |
| Absolute oral bioavailability | Not applicable | 0.45% |
The authors compared inotodiol’s very low oral absorption to that of other fat-soluble plant sterols. These are mouse data for one isolated compound. They do not describe what happens when a person drinks chaga tea or takes a powder.
Regulatory status
In the US, chaga products are sold as dietary supplements. Under the Dietary Supplement Health and Education Act (DSHEA), FDA does not have the authority to approve dietary supplements before they are marketed, and it does not approve their labeling (FDA). Product quality, dose and oxalate content are therefore not standardized.
Chaga is not named anywhere on the WADA 2026 Prohibited List.
What the research shows
Human studies
A 2024 review of chaga and two related medicinal fungi found only two clinical studies of chaga in the peer-reviewed literature, both carried out more than four decades ago (Tee et al., Fungal Biol Biotechnol 2024):
| Study population | n | Reported outcome |
|---|---|---|
| Psoriasis | 50 | Clearing or improvement of skin lesions |
| Peptic ulcer, three dose groups | 58 | Temporary pain relief, larger at higher doses; pain returned after stopping |
The review describes these as early reports, not modern randomized trials. It also states that no controlled trials of chaga’s safety were identified and that no relevant studies were registered on ClinicalTrials.gov. An earlier review was blunter: “To date, no human experiments have been performed” (Szychowski et al., 2021). MSK likewise states that the safety and efficacy of chaga have yet to be evaluated in clinical studies (MSK About Herbs).
One study is sometimes cited as human evidence, but it was a test-tube experiment using human cells. Researchers took white blood cells (lymphocytes) from 20 people with inflammatory bowel disease and 20 healthy volunteers, then exposed them to hydrogen peroxide in the lab. Adding chaga extract to the dish reduced the resulting DNA damage by 54.9% in patients’ cells and 34.9% in healthy volunteers’ cells (Najafzadeh et al., Biofactors 2007). Nobody ate chaga in this study.
Exercise and fatigue (animal data)
Interest in chaga for “recovery” rests mostly on rodent studies. In one, male mice (n = 8 per group) received chaga extract by mouth at 824, 1,648 or 2,472 mg/kg once daily for 6 weeks. Treated mice had more muscle volume, longer treadmill time to exhaustion and higher glycogen stores than controls (Chen et al., Nutrients 2022). The mice did not train, and these results have not been tested in people.
Blood sugar (animal and cell data)
In mice with chemically induced diabetes, chaga polysaccharides at 50 mg/kg for 4 weeks lowered fasting blood glucose and raised serum insulin (Wang et al., PLoS One 2017). In lab assays, chaga terpenoids inhibit alpha-glucosidase, an enzyme that breaks down dietary carbohydrate (MSK About Herbs). No human trial has tested whether chaga lowers blood sugar.
Cancer (cell and animal data)
Chaga’s folk reputation is strongest for cancer. Extracts slow the growth of many cancer cell lines in culture. For example, a water extract arrested the cell cycle and triggered cell death in human liver cancer (HepG2) cells (Youn et al., World J Gastroenterol 2008), and extracts from three countries were toxic to four tumor cell lines but not to primary pig liver cells (Glamočlija et al., 2015). Killing cells in a dish is a low bar that many substances clear. There are no controlled trials of chaga in people with cancer.
Side effects and risks
MSK’s patient summary says there are no reports of side effects from chaga, but its professional section lists the kidney cases below (MSK About Herbs). Without trials, there are no measured rates of side effects.
Oxalate kidney damage
Oxalate is a natural compound that can bind calcium and form crystals. When large amounts are absorbed, crystals can lodge in the kidney tubules and damage them (oxalate nephropathy). Three published case reports describe this after chaga use:
| Case | Chaga intake | Outcome |
|---|---|---|
| 72-year-old woman with liver cancer, Japan | 4–5 teaspoons of powder daily for 6 months | Oxalate crystals on kidney biopsy; hemodialysis started (Kikuchi et al., Clin Nephrol 2014) |
| 49-year-old man with atopic dermatitis, Korea | 3 g/day for 4 years, then 9 g/day for 1 year | End-stage kidney disease; still on maintenance hemodialysis 18 months later (Lee et al., J Korean Med Sci 2020) |
| 69-year-old man, Korea | 10–15 g/day for 3 months, plus vitamin C 500 mg/day | Acute kidney injury with nephrotic syndrome; recovered after dialysis and high-dose steroids (Kwon et al., Medicine 2022) |
In the 2020 Korean case, the doctors measured the patient’s leftover chaga powder. It contained 14.2 g of oxalate per 100 g (0.14 g per gram). Two other companies’ products contained 2.8 and 11.2 g per 100 g (Lee et al., 2020). The authors estimated the patient’s intake at 420–1,260 mg of oxalate a day from chaga alone. For comparison, they note that typical diets contain about 200–300 mg of oxalate a day, and that the goal for people trying to prevent kidney stones is under 100 mg a day.
A follow-up study in rats tested this directly. Rats were fed chaga powder at 1,281.6 mg/kg (standard dose) or 3,844.8 mg/kg (high dose) for 16 weeks (n = 6 per group). The high-dose group developed oxalate crystal deposits, tubular injury and more protein in the urine than controls (p = 0.001), and gained less weight (Lee et al., J Korean Med Sci 2026).
The case authors note that kidney damage from chaga may be underrecognized. The link is easy to miss unless a kidney biopsy is done and doctors ask about health foods, and measuring a product’s oxalate content is not available in routine practice (Lee et al., 2020). The same authors list other causes of oxalate nephropathy, including excess vitamin C (ascorbic acid) intake and enteric hyperoxaluria (increased oxalate absorption from the gut). One of the three chaga cases was also taking vitamin C.
Bleeding risk
A small peptide isolated from chaga mycelium inhibited platelet aggregation (clumping) in the lab and in mice (Hyun et al., Peptides 2006). On this basis, MSK flags a possible additive effect with anticoagulant and antiplatelet drugs such as warfarin, while noting that the clinical relevance is unknown (MSK About Herbs).
Diabetes medicines
Because chaga lowered glucose in animal and lab studies, MSK lists a possible additive effect with glucose-lowering drugs, again with unknown clinical significance (MSK About Herbs).
Product variability
Chaga products are not standardized. Oxalate content varied about five-fold across the three commercial powders measured in Korea (Lee et al., 2020). Reviewers also note that sclerotia should be harvested away from pollution sources, because the fungus may accumulate contaminants (Szychowski et al., 2021).
Key takeaways
- A birch fungus, not a tested medicine. Chaga is the sterile conk of Inonotus obliquus, used in folk medicine and sold in the US as a dietary supplement that FDA does not pre-approve.
- No modern human trials. Reviews found only two clinical reports, both more than 40 years old, and no controlled safety trials.
- Benefits are from cells and rodents. Effects on endurance, blood sugar and cancer cells come from mouse and test-tube studies and have not been shown in people.
- High in oxalate. Commercial powders contained 2.8–14.2 g of oxalate per 100 g, and three case reports link chaga use to oxalate kidney damage, including permanent kidney failure.
- Possible drug interactions. Lab and animal data suggest additive effects with blood thinners and glucose-lowering drugs; clinical relevance is unknown.
- No established half-life. The only kinetic data are for one constituent, inotodiol, in mice, where oral bioavailability was 0.45%.
Sources
- Szychowski KA, Skóra B, Pomianek T, Gmiński J. Inonotus obliquus - from folk medicine to clinical use. J Tradit Complement Med. 2021;11(4):293–302. PubMed.
- Tee PYE, Krishnan T, Cheong XT, et al. A review on the cultivation, bioactive compounds, health-promoting factors and clinical trials of medicinal mushrooms Taiwanofungus camphoratus, Inonotus obliquus and Tropicoporus linteus. Fungal Biol Biotechnol. 2024;11(1):7. PubMed.
- Glamočlija J, Ćirić A, Nikolić M, et al. Chemical characterization and biological activity of Chaga (Inonotus obliquus), a medicinal “mushroom”. J Ethnopharmacol. 2015;162:323–332. PubMed.
- Kim JH, Gao D, Cho CW, et al. A Novel Bioanalytical Method for Determination of Inotodiol Isolated from Inonotus Obliquus and Its Application to Pharmacokinetic Study. Plants (Basel). 2021;10(8):1631. PubMed.
- Najafzadeh M, Reynolds PD, Baumgartner A, et al. Chaga mushroom extract inhibits oxidative DNA damage in lymphocytes of patients with inflammatory bowel disease. Biofactors. 2007;31(3-4):191–200. PubMed.
- Chen YM, Chiu WC, Chiu YS. Effect of Inonotus obliquus Extract Supplementation on Endurance Exercise and Energy-Consuming Processes through Lipid Transport in Mice. Nutrients. 2022;14(23):5007. PubMed.
- Wang J, Hu W, Li L, et al. Antidiabetic activities of polysaccharides separated from Inonotus obliquus via the modulation of oxidative stress in mice with streptozotocin-induced diabetes. PLoS One. 2017;12(6):e0180476. PubMed.
- Youn MJ, Kim JK, Park SY, et al. Chaga mushroom (Inonotus obliquus) induces G0/G1 arrest and apoptosis in human hepatoma HepG2 cells. World J Gastroenterol. 2008;14(4):511–517. PubMed.
- Kikuchi Y, Seta K, Ogawa Y, et al. Chaga mushroom-induced oxalate nephropathy. Clin Nephrol. 2014;81(6):440–444. PubMed.
- Lee S, Lee HY, Park Y, et al. Development of End Stage Renal Disease after Long-Term Ingestion of Chaga Mushroom: Case Report and Review of Literature. J Korean Med Sci. 2020;35(19):e122. PubMed.
- Kwon O, Kim Y, Paek JH, et al. Chaga mushroom-induced oxalate nephropathy that clinically manifested as nephrotic syndrome: A case report. Medicine (Baltimore). 2022;101(10):e28997. PubMed.
- Lee S, Cui S, Fang X, et al. Kidney Injury Induced by High-Dose Chaga Mushroom Consumption: Experimental Evidence in a Rat Model. J Korean Med Sci. 2026;41(3):e37. PubMed.
- Hyun KW, Jeong SC, Lee DH, et al. Isolation and characterization of a novel platelet aggregation inhibitory peptide from the medicinal mushroom, Inonotus obliquus. Peptides. 2006;27(6):1173–1178. PubMed.
- Memorial Sloan Kettering Cancer Center. About Herbs, Botanicals and Other Products: Chaga Mushroom. Last updated February 20, 2023. MSK.
- Food and Drug Administration. Questions and Answers on Dietary Supplements. FDA.
- World Anti-Doping Agency. The 2026 Prohibited List. In effect from January 1, 2026. WADA 2026 Prohibited List.