Chaga Side Effects, Oxalates and Kidney Concerns

Kidney warning first. Doctors in Japan and Korea have published case reports of serious kidney injury in people who took chaga (Inonotus obliquus) powder, with oxalate crystals found in kidney tissue. In two of three cases summarized by Memorial Sloan Kettering Cancer Center (MSK), dialysis was needed and kidney function did not recover. [1] If you have kidney disease, reduced kidney function or a kidney transplant, ask your kidney specialist or pharmacist before using chaga in any form. This page describes reports and is not advice for any one person.

What chaga is

Chaga is Inonotus obliquus (Fr.) Pilát, family Hymenochaetaceae, an accepted fungal species. [2] MSK says it is commonly found on birch trees in cold climates and is used in folk medicine across northern Europe, and that the conk used medicinally includes wood from the host tree together with the fungus. [1] For the full profile see chaga.

What the case reports describe

The amounts are what each report recorded. They are not safe or unsafe thresholds, and they are not recommendations. The authors of the 2014 report called these mushrooms extremely high in oxalate, and the 2020 authors called chaga a potential risk factor for chronic kidney disease given its oxalate content. [3][4]

Animal evidence

A 2026 study in rats gave chaga powder at amounts scaled from a clinical case. The highest-dose group had oxalate crystal deposits, tubular injury and more protein in the urine; the authors concluded that high-dose consumption may damage the kidneys. [6] This is animal research at high amounts and does not tell us the risk to a person who uses a small amount.

What is not known

• How common this is. We found case reports only, with no study counting how often it happens. Case reports can show a problem exists but cannot show how likely it is.
• Whether tea, extracts and capsules carry the same risk. The reports describe powder. Oxalate content of tea or extracts is not described in the sources we read. MSK's patient text says it is generally safe to drink as a tea, while its clinician section lists the kidney cases, so ask a clinician rather than assume. [1] See chaga tea, powder and extracts.
• Who is most at risk. The sources we read do not define it, so asking a kidney specialist first is the cautious course.

Medicine cautions

MSK says to talk with your healthcare provider if you take blood thinners such as warfarin, because chaga may increase bleeding risk. [1] Its clinician section notes that chaga extract inhibited platelet clumping in mice and that the clinical relevance is not known, and that chaga had additive blood-sugar-lowering effects in laboratory tests with unknown clinical significance. [1] Ask a pharmacist before combining chaga with blood thinners, antiplatelet medicines or diabetes medicines, and tell the surgical team before any procedure. See how interactions work and supplements before surgery.

Other groups

Pregnancy, breastfeeding, children, older adults and liver safety are not described for chaga in the sources we read. Contamination and mislabeling of chaga products are not described either; see quality testing and certifications. MSK also says natural reserves of the fungus have nearly been exhausted and that scientists are seeking cultivated substitutes, which is one reason the species label and source matter. [1]

When to get help

If you feel unwell or notice any change in your health while using chaga, stop it and contact a clinician promptly. Call 911 for collapse or severe symptoms. To report a reaction see side effects and reporting. For wider kidney questions see mushrooms, the kidneys, oxalates and the liver and minerals and kidney disease.