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Chaga mushroom is a dark, crusty fungus that grows on birch trees in cold northern forests and is sold as tea, powders and capsules. It is marketed with a long list of benefits, but every one of them comes from lab and animal studies: Memorial Sloan Kettering Cancer Center (MSKCC) notes that chaga’s safety and efficacy have yet to be evaluated in clinical studies. Meanwhile, case reports have linked long-term chaga powder to serious kidney damage. Here is what chaga is, what the research shows and who should be careful.
Peptide Labs sells no chaga products, and this article does not recommend any product. It is general information, not medical advice.
Key Takeaways
- Chaga (Inonotus obliquus), also called birch conk or cinder conk, grows on birch trees in cold climates.
- Its suggested benefits come from cell and animal studies; no clinical trials have tested them in people.
- Chaga is very high in oxalate, and case reports link long-term chaga powder to kidney failure.
- Chaga may add to bleeding risk with warfarin and similar drugs, and lab data suggest effects on blood sugar.
- Wild chaga has been heavily harvested, and researchers are working on cultivated substitutes.
What is chaga mushroom?
Inonotus obliquus is a fungus that infects birch trees and forms a hard, black, cracked mass on the trunk, which is why it is also called cinder conk, birch conk or clinker polypore. MSKCC notes that the conk used for supplements is a mix of wood from the host tree and the fungus itself. Chaga has been used as a folk remedy in Russia and other northern European countries. It is technically edible but very bitter, so people usually drink it as chaga tea, and supplements come as tablets, capsules and powders.
Chaga is also a frequent ingredient in mushroom blends; our guide to mushroom coffee covers those products. MSKCC adds a sustainability note: natural reserves of wild chaga have nearly been exhausted, and scientists are trying to develop cultivated substitutes.
Chaga mushroom benefits: what the research shows
Search results promise chaga mushroom benefits for immunity, inflammation, blood sugar and more. MSKCC lists many effects seen in preclinical research, meaning test tubes and animals, but says chaga has not been evaluated in clinical studies. That gap matters: many compounds that look strong in a dish do nothing, or cause harm, in people.
| Claim you may see | What the evidence is | Human trials |
|---|---|---|
| Immune support | Cell and animal studies of chaga extracts | None found |
| Inflammation | Animal models and lab enzyme studies | None found |
| Blood sugar | Lab studies showing enzyme effects; additive effects in vitro | None found |
| Antioxidant | Lab measurements of chaga compounds | None found |
| Tumor-related claims | Cell and mouse studies only | None found |
Antioxidant capacity in a lab test does not show that a food or supplement improves health, and claims that chaga fights cancer or any other disease are not supported and are not allowed on supplement labels. A useful trial would compare chaga with placebo in people, measure real health outcomes rather than lab markers, and track side effects over months, including kidney function. No such trial was found. Anyone in care for a serious illness should talk with their medical team before taking chaga, partly because of the interaction issues below.
Chaga side effects: the oxalate and kidney problem
MSKCC’s patient summary says there are no general reports of chaga side effects, but its professional section lists serious adverse reactions, and they all point to the same issue. Chaga contains oxalic acid, and a 2014 report described chaga as having extremely high oxalate concentrations. Oxalate can form crystals in the kidneys, a condition called oxalate nephropathy.
- Japan, 2014: a 72-year-old woman who took chaga powder daily for six months developed oxalate nephropathy and needed dialysis; MSKCC notes her kidney function did not recover. It was the first reported case.
- Korea, 2020: a 49-year-old man developed end-stage kidney disease after long-term chaga powder use. A kidney biopsy showed oxalate crystals, and the remaining chaga he had tested very high in oxalate.
- Korea, 2022: a 69-year-old man who took chaga powder along with vitamin C for three months developed acute kidney injury from oxalate. His kidney function recovered after dialysis and steroids.
These are case reports, so they cannot show how common the problem is, but the damage was severe and involved regular use of concentrated powder over months. People with kidney disease, a history of kidney stones or high oxalate levels should avoid chaga supplements unless their doctor agrees. Large amounts of vitamin C from supplements can add to the body’s oxalate load, which was a factor in the 2022 case. Seek medical care if you notice reduced urination, swelling in the legs or unusual fatigue.
Chaga with warfarin and diabetes medicines
MSKCC advises talking with your provider if you take blood thinners such as warfarin, because chaga may increase bleeding risk. The evidence comes from an animal study in which chaga extract slowed platelet clumping; the clinical importance is unknown, but the cautious approach is to involve your prescriber and tell your surgeon or dentist before any procedure. Our nattokinase guide covers a similar bleeding question with another popular supplement.
- Diabetes medicines: in lab studies chaga had additive blood sugar lowering effects. The real-world significance is unknown, but anyone using insulin or other glucose-lowering drugs should ask their prescriber first. Our guide to berberine side effects covers the same caution for another supplement marketed around blood sugar.
- Pregnancy and breastfeeding: there are no human safety data, so avoid chaga supplements unless your clinician agrees.
- Before surgery: tell your care team about every supplement you take, including teas.
How to read a chaga label
Chaga products range from chunks for brewing tea to powders and hot-water or alcohol extracts, and the kidney cases above involved powders taken for months. A clear label names Inonotus obliquus, says whether the product is whole conk or an extract and whether it is wild or cultivated, and carries a full Supplement Facts panel with the standard FDA disclaimer. Few labels state oxalate content, so do not assume a product is low in it.
Independent testing can confirm identity and screen for contaminants; see our guide to third-party tested supplements. If you are comparing mushroom supplements, our lion’s mane guide reviews a mushroom that has at least some small human trials.
Frequently Asked Questions
What are the main chaga mushroom benefits?
Chaga is marketed for immunity, inflammation and blood sugar, but those ideas come from lab and animal studies. MSKCC says chaga has not been evaluated in clinical studies.
What are chaga side effects?
The main concern is kidney damage from oxalate: case reports link months of chaga powder to oxalate nephropathy and kidney failure. Chaga may also add to bleeding risk with blood thinners.
Is chaga tea safe?
MSKCC says it is generally safe to eat chaga and drink it as tea, but concentrated supplements need more caution. People with kidney problems or who take blood thinners or diabetes medicines should ask a clinician first.
Can I take chaga with warfarin?
Talk to your prescriber first. MSKCC warns chaga may increase bleeding risk with blood thinners such as warfarin.
What is Inonotus obliquus?
It is the scientific name for chaga, a fungus that grows on birch trees in cold climates and is also called birch conk or cinder conk.
Who should avoid chaga supplements?
People with kidney disease or a history of kidney stones, people who take blood thinners or diabetes medicines, anyone preparing for surgery, and people who are pregnant or breastfeeding should avoid chaga supplements unless their clinician agrees.
Is chaga sustainable?
MSKCC notes that wild chaga reserves have nearly been exhausted and that scientists are developing cultivated substitutes. Check whether a label says wild or cultivated.
Questions about a label? Contact us or read our Buyer’s Guide. Follow the label and ask a healthcare provider before starting any supplement, especially if you take medicines or are pregnant. These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.
Last reviewed October 2026.
Related guides: Mushroom Coffee: Benefits, Caffeine and Is It Healthy?, Reishi Mushroom Benefits: Evidence, Liver Safety and Warfarin, Lion’s Mane: What the Research Shows and Side Effects.