Chaga (Inonotus obliquus)

What it is

Chaga, in German Schiefer Schillerporling, is a fungus that grows mainly on birch trees. In Russia it is traditionally brewed as tea; in the Soviet Union there was even a chaga preparation called Befungin.

In Germany, chaga is offered as powder, capsules, extract or tea and counts among the so-called medicinal mushrooms. The German consumer advice centre (Verbraucherzentrale) describes it as a fungus traditionally used in Russia that is becoming increasingly popular in Germany. The fungus contains, among other things, polysaccharides such as beta-glucans, triterpenes such as inotodiol and plenty of oxalic acid.

How it is supposed to work

The promises range from immune strengthening to blood sugar regulation to anti-aging. A review summarizes the laboratory findings: blood sugar lowering and insulin-sensitizing effects, antiviral and antiparasitic activity, and an effect on antioxidant enzymes. The receptor PPAR-gamma, which is involved in inflammation and sugar metabolism, is discussed as a possible switching point.

An example of the kind of data: in the test tube, chaga extract reduced the DNA damage in white blood cells caused by hydrogen peroxide, by 54.9 percent in people with chronic inflammatory bowel disease and by 34.9 percent in healthy people. That is a clean laboratory finding. Whether drinking chaga tea gets enough of these substances into the cells to achieve something similar has not been studied.

Chaga is often advertised with a particularly high ORAC value, a laboratory value for antioxidant capacity. The US Department of Agriculture withdrew its ORAC database back in 2012, because these values do not allow any statement about effects in the human body and were routinely used by manufacturers for advertising.

What is known about its use

The long tradition as a tea is real. A recent review states that the assessment of chaga’s safety and efficacy has so far rested almost entirely on this tradition. Controlled studies on safety do not exist. A number of studies with chaga are now listed in the US trial registry, some as part of blends. A completed study with its own chaga arm of 20 healthy people over one month has to this day not posted any results.

What matters in practice is quality. Ground powder and water or alcohol extracts are on offer, and the products differ greatly. Across just three measured commercial powders, the oxalate content ranged from 2.8 to 14.2 g per 100 g. The authors of this case report therefore call for clear quantity limits based on the oxalate content of the respective product. Such limits do not yet exist either in the EU or in Germany.

What the studies show

Psoriasis, 1973

In a Soviet study, 50 people with psoriasis received a chaga preparation. According to the report, the skin lesions disappeared completely in 38 and improved markedly in 8. There was neither a control group nor blinding, so the effect cannot be separated from the natural course.

Stomach ulcer, 1981

A second Soviet paper treated 58 patients with stomach ulcers with the chaga preparation Befungin in three dose groups. The pain subsided temporarily, more so at the higher dose, and returned after stopping. Here, too, a placebo group is missing.

Kidney failure after five years

A 49-year-old Korean man took chaga powder for atopic dermatitis for 5 years, initially 3 g daily for 4 years, then 9 g for another year. He developed end-stage kidney failure, and the biopsy showed oxalate deposits. A second case involved a 72-year-old Japanese woman who became dependent on dialysis after 6 months of 4 to 5 teaspoons daily.

Acute kidney failure with recovery

A 69-year-old man took 10 to 15 g of chaga powder daily for 3 months together with 500 mg of vitamin C, which can also be broken down to oxalate in the body. He developed acute kidney failure with oxalate crystals. After dialysis and cortisone, kidney function recovered within a month.

Where the data stop

For none of the advertised effects is there a controlled study in humans. The two Soviet papers are over 40 years old, unblinded and without a comparison group. Claims about the immune system, blood sugar, inflammation, the gut or cancer rest on cell culture and animal experiments. For the frequently cited support of the gut lining, too, we did not find a single human study. Memorial Sloan Kettering Cancer Center states that the safety and efficacy of chaga have not yet been tested in clinical studies, and the Verbraucherzentrale sees no evidence of healing effects.

On top of this comes a remarkable contradiction. In diabetic rats, chaga protected the kidneys; in humans, it is precisely kidney damage that is documented. How often such damage occurs cannot be derived from three case reports. And because the oxalate content varies greatly between products, the amount on the package says little about how much oxalate you actually take in.

Status, approval and legal

In Germany, chaga is sold as a food supplement. According to the EU Novel Food Catalogue, fruiting bodies as well as water and ethanol extracts in food supplements are not considered novel. For foods other than food supplements, by contrast, the Finnish authority has classified the fungus as novel; there it would need authorization. According to our research, there is no approved medicine containing chaga in Germany, and food supplements may in principle not be credited with healing effects. Because there is neither an approval nor dosing studies, we do not give a dosage. Chaga is not on the WADA prohibited list for 2026.

Safety

The central risk is the kidneys. Three published cases show oxalate nephropathy after chaga powder, two of them with permanent dialysis. Anyone who has had kidney stones, has impaired kidney function or additionally takes high-dose vitamin C should avoid chaga. In a mouse model, chaga extract inhibited blood platelets, so caution is advised with anticoagulants and before surgery, even though the clinical significance is unclear. In the lab, chaga enhanced blood sugar lowering effects; anyone taking diabetes medication should discuss this with a doctor. There is no official upper limit, and systematic safety studies in humans are lacking. For pregnant and breastfeeding women and for children there are no data whatsoever, not even on how the oxalate affects them.

Sources

• Tee et al., Fungal Biol Biotechnol 2024 – review including clinical studies
• Szychowski et al., J Tradit Complement Med 2021 – Inonotus obliquus, from folk medicine to clinical use
• Lee et al., J Korean Med Sci 2020 – end-stage kidney failure after chaga
• Kikuchi et al., Clin Nephrol 2014 – oxalate nephropathy caused by chaga
• Kwon et al., Medicine 2022 – acute oxalate nephropathy
• Lee et al., J Korean Med Sci 2026 – kidney damage from chaga in a rat model
• Memorial Sloan Kettering Cancer Center – About Herbs: Chaga
• Verbraucherzentrale (German consumer advice centre) – Medicinal mushrooms for cancer therapy?
• EU Novel Food Catalogue – Inonotus obliquus
• Najafzadeh et al., Biofactors 2007 – chaga extract and DNA damage in vitro