Quick answer
The best-documented side effect of chaga is kidney damage from its oxalate. At least three people who took chaga powder daily for 3 months to 5 years developed it, and one stayed on dialysis. Other side effects are rarely reported, and we found no trial that measured them.1,2,3
Key facts
- In the five-year case, kidney function never came back, and the man was still on dialysis 18 months later.1
- In the three-month case, kidney function recovered within a month of dialysis and steroids.2
- The man in the five-year case had normal kidney checkups until two years before he was admitted.1
- A chaga peptide slowed platelet clumping in lab tests and in mice.4
Kidney damage from oxalate
Oxalate nephropathy, kidney damage from oxalate crystals, has been reported in at least three people who took chaga powder every day for months or years.1,2,3
A 72-year-old woman under treatment for liver cancer took 4 to 5 teaspoons of chaga powder a day for six months and needed dialysis for oxalate kidney damage.3
A 49-year-old man who took 3 g of chaga powder a day for four years, then 9 g a day for a year, developed kidney failure and was still on dialysis 18 months later.1
A 69-year-old man who took 10 to 15 g of chaga powder a day, with 500 mg of vitamin C, for three months developed acute kidney injury. His kidneys recovered after dialysis and steroid treatment.2
In the five-year case, the first sign was nausea and vomiting, and by then the kidneys had already failed. His routine checkups had been normal two years earlier, so the damage developed between checkups.1
In a 2026 study in rats, the higher of two doses of chaga powder caused oxalate crystal deposits and kidney injury.5
Who is most at risk
No study has worked out who is most at risk. The case reports and basic oxalate chemistry point to people with reduced kidney function or a history of kidney stones, people who also take vitamin C supplements, which can add to the oxalate load, and anyone taking large daily amounts for months.1,2
- Do not take chaga if you have kidney disease or have had kidney stones, unless your kidney doctor agrees
- Ask first if you take vitamin C supplements, a blood thinner, or medicine that lowers blood sugar
- Ask first if you are pregnant, breastfeeding or under cancer care
- Tell your doctor if you have taken chaga regularly, so your kidney function can be checked if needed
Other possible effects
Other side effects of chaga are rarely reported in the medical literature.1
Two lab findings suggest caution with some medicines. A peptide from chaga slowed platelet clumping in lab tests and in mice, which could matter for people on blood thinners. Chaga polysaccharides lowered blood sugar in mice, which could matter for people on glucose-lowering medicines. Neither effect has been tested in people.4,6
None of the official sources we use covers chaga, so no interaction with a specific medicine is documented. That is a gap in the research, not a sign of safety, so tell your pharmacist you take it.
Claims to be wary of
In a March 2026 warning letter, the FDA found that a company had marketed its chaga extract, along with turkey tail and red reishi, by citing research on illness, which made them unapproved new drugs.7
Supplements may not be sold as treatments for cancer or viruses. The cell studies that sellers cite do not show what chaga does in a person, and a product sold with those claims has not been through the approval a medicine needs.7,8
Questions people ask
Is chaga safe to consume?
No safe amount has been established. Three people developed kidney damage after months to years of daily chaga powder, and people with kidney problems should not take it without their doctor's agreement.1,2,3
Does chaga cause stomach problems?
We found no study of chaga's effects on the stomach. Nausea and vomiting were the first signs of kidney failure in one chaga case, so do not dismiss them if you take chaga regularly.1
Does chaga tea have the same risks?
The same concern applies, though its size is unknown. Water extracts of chaga, which is what a tea is, contained oxalic acid as their main organic acid, but no study we found measured the oxalate in a cup.8
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Sources
- Lee S, Lee HY, Park Y, Ko EJ, Ban TH, Chung BH, Lee HS, Yang CW. 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. Opened 2026-10-07.
- Kwon O, Kim Y, Paek JH, Park WY, Han S, Sin H, Jin K. Chaga mushroom-induced oxalate nephropathy that clinically manifested as nephrotic syndrome: A case report. Medicine (Baltimore). 2022;101(10):e28997. Opened 2026-10-07.
- Kikuchi Y, Seta K, Ogawa Y, Takayama T, Nagata M, Taguchi T, Yahata K. Chaga mushroom-induced oxalate nephropathy. Clin Nephrol. 2014;81(6):440-444. Opened 2026-10-07.
- Hyun KW, Jeong SC, Lee DH, Park JS, Lee JS. Isolation and characterization of a novel platelet aggregation inhibitory peptide from the medicinal mushroom, Inonotus obliquus. Peptides. 2006;27(6):1173-1178. Opened 2026-10-07.
- Lee S, Cui S, Fang X, Lee H, Lim SW, Shin YJ, Li C, Yang CW, Chung BH. Kidney Injury Induced by High-Dose Chaga Mushroom Consumption: Experimental Evidence in a Rat Model. J Korean Med Sci. 2026;41(3):e37. Opened 2026-10-07.
- Wang J, Wang C, Li S, Li W, Yuan G, Pan Y, Chen H. Anti-diabetic effects of Inonotus obliquus polysaccharides in streptozotocin-induced type 2 diabetic mice and potential mechanism via PI3K-Akt signal pathway. Biomed Pharmacother. 2017;95:1669-1677. Opened 2026-10-07.
- U.S. Food and Drug Administration. Warning letter, MARCS-CMS 720213, March 6, 2026. Opened 2026-10-07.
- Glamočlija J, Ćirić A, Nikolić M, Fernandes Â, Barros L, Calhelha RC, Ferreira IC, Soković M, van Griensven LJ. Chemical characterization and biological activity of Chaga (Inonotus obliquus), a medicinal "mushroom". J Ethnopharmacol. 2015;162:323-332. Opened 2026-10-07.
This page is information, not medical advice. Talk to your doctor or pharmacist about your own situation.