Quick answer

No study has tested whether chaga causes kidney stones. Case reports describe kidney damage from oxalate crystals in people who took chaga powder daily for months or years, and chaga powders held 2.8 to 14.2 g of oxalate per 100 g. Ask your doctor first if you have kidney disease or have had stones.^1,2,3

Key facts

We found no trial of chaga on its own in people and no study that counted kidney stones in people who take it.¹
The published reports describe oxalate nephropathy, kidney injury with oxalate crystals found in kidney tissue, in people who took chaga powder daily for 3 months to 5 years.^1,2,3
MedlinePlus says oxalate is the most common substance that combines with calcium to form kidney stones, and that it is found in certain foods and in vitamin C supplements.⁴
Chaga powders from three companies held 2.8, 11.2 and 14.2 g of oxalate per 100 g, against a typical diet that supplies 200 to 300 mg a day.¹
No upper limit or safe daily amount has been set for chaga.^1,2

What the chaga reports describe

Three case reports link chaga powder to kidney damage, and a 2026 rat study points the same way. In each person, a kidney biopsy showed calcium oxalate crystals inside the kidney's tubules, a condition called oxalate nephropathy. The abstracts we read describe crystals found in biopsy tissue and do not describe kidney stones.^1,2,3,5

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 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

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

Case reports show that something happened to a few people. They cannot say how often it happens, who is at risk, or how much chaga it takes. The authors of the reports tied the damage to chaga's very high oxalate content.¹

Is oxalate kidney damage the same as kidney stones?

No. They are different problems that involve the same substance. MedlinePlus describes a kidney stone as a solid piece of material that forms in the kidney from substances in the urine, and says oxalate is the most common of the substances that combine with calcium to form the most common kind of stone. It names spinach and vitamin C supplements as sources of oxalate.^4,6

The National Institute of Diabetes and Digestive and Kidney Diseases adds that people who have had calcium oxalate stones may be told to avoid foods high in oxalate. Whether chaga raises the chance of forming a stone has not been studied that we could find. The high oxalate content is a reason for caution, not a finding.⁷

How much oxalate is in chaga?

Chaga powders from three companies held 2.8 g, 11.2 g and 14.2 g of oxalate per 100 g.¹

At 0.14 g of oxalate per gram of powder, 3 g of chaga a day supplies about 420 mg of oxalate, and 9 g about 1,260 mg.¹

A typical diet supplies 200 to 300 mg of oxalate a day.¹

Water and alcohol extracts of chaga from Finland, Russia and Thailand all contained oxalic acid as their main organic acid, the most in a Russian water extract.⁸

These figures come from powders measured in one case report. None of the sources we read measured the oxalate in chaga tea, so the figures say nothing about how much a cup holds.^1,8

Who should ask their doctor before using chaga

People with kidney disease, and people who have had kidney stones, should ask their doctor first. A kidney doctor may want to be part of that talk.¹
People who take vitamin C supplements should ask their doctor or pharmacist, because vitamin C is another source of oxalate and one of the reports involved a person who took 500 mg of it a day alongside chaga.^2,4
Anyone who has taken chaga every day for months can ask their doctor whether kidney function should be checked.¹
People who are pregnant, breastfeeding or under treatment for cancer should ask their doctor, because no source we found covers chaga in those situations.¹

In a 2026 study in rats, the higher of two doses of chaga powder caused oxalate crystal deposits and kidney injury.⁵

What the sources do not tell us

NIH's National Center for Complementary and Integrative Health has no page on chaga, and the NIH LiverTox database has no chaga chapter that we could find. Without an official review, the reports above are what there is.

That leaves case reports and one animal study as the record of harm. A short list of reports is not proof that most people are at risk, and it is not proof that nobody is.¹

Questions people ask

Does chaga cause kidney stones?

No study has tested that. Published case reports describe oxalate crystals damaging the kidneys of people who took chaga powder every day, and MedlinePlus names oxalate as the most common substance in calcium kidney stones.^1,4

Can chaga damage your kidneys?

Case reports describe kidney damage, including kidney failure needing dialysis, in people who took chaga powder daily for months to years. Ask your doctor first if you have kidney disease.^1,2,3

Does chaga cause liver damage?

The reports we read describe kidney injury, not liver injury, and LiverTox has no chaga chapter. That is not a finding either way, so ask your doctor if you have liver disease.¹

Is chaga tea high in oxalate?

We found no source that measured the oxalate in chaga tea. The measured figures are for powders from three companies.¹

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Sources

This page is information, not medical advice. Talk to your doctor or pharmacist about your own situation.