Chaga side effects: oxalate, kidneys, and who should be careful?

Short answer: The best-known side effect of chaga is related to oxalate: there are three case reports of severe kidney damage after taking chaga powder daily for months to years. Little is known about other side effects because good studies in humans are lacking. If you take blood thinners or blood sugar-lowering medication, have (had) kidney problems, or are pregnant, consult your doctor or pharmacist first.

Last updated: November 4, 2026 · Written by Florian Fermin

Online, you mainly read about all the things chaga is supposed to do. You read much less about the downsides. So here we’ve gathered what is known about its side effects, what isn’t, and when to check with your doctor first.

Chaga (Inonotus obliquus, known in English as the birch polypore) is a fungus that grows on birch trees as a hard, black conk. It is available as a powder, capsules, and extract.

What side effects of chaga are known?

The main known side effect of chaga is kidney damage caused by oxalate after long-term use of large amounts of chaga. This is based on three case reports and an animal study. In addition, laboratory and animal studies have examined effects on blood clotting and blood sugar, which is relevant if you take medication. Other side effects have barely been studied in humans.

Why is oxalate in chaga a concern?

Oxalate is a salt of oxalic acid, which is also found in spinach and rhubarb, and can bind to calcium in the body. If you consume a lot of it over a long period, calcium oxalate crystals can build up in the kidneys. That is exactly what doctors observed in patients who used a lot of chaga (Kikuchi et al., 2014; Lee et al., 2020; Kwon et al., 2022).

Chaga contains a lot of it. In a Korean report, the patient’s chaga powder was tested and found to contain 14.2 g of oxalate per 100 g. Powders from two other manufacturers contained 2.8 and 11.2 g per 100 g (Lee et al., 2020). So the content varies considerably between products. The same researchers say that a typical diet contains 200 to 300 mg of oxalate per day.

Oxalate dissolves in water. So chaga tea and extract also contain it, not just the powder. Our label doesn’t list the oxalate content.

What do patient reports show about chaga and the kidneys?

We found three patient reports in PubMed in which doctors linked kidney damage to chaga. In each case, the people had taken chaga powder every day for months to years.

What do these reports tell us, and what don’t they? They show that it can happen, not how often it happens. They involve three people, and in two cases the amount was substantially higher than what our packaging recommends (1 to 3 g per day). At the same time, the man in Lee’s report first took 3 g per day for four years, exactly as his manufacturer advised, before increasing to 9 g. To be honest, we can’t promise that staying within the daily dose guarantees everything will be fine. There simply isn’t any long-term research in people.

In a 2026 rat study, the animals were given chaga powder in two doses. At the higher dose, the researchers found oxalate crystals and kidney damage (Lee et al., 2026). A rat isn’t a person, but the findings are consistent with what the patient reports show.

The researchers in the 2020 report also mention excessive vitamin C intake as another known cause of oxalate in the kidneys. If you take a high dose of vitamin C in addition to chaga, discuss it with your doctor.

Can chaga interact with blood thinners or diabetes medication?

Whether chaga interacts with blood thinners or diabetes medication has not been studied in people. The available evidence comes from lab and animal studies. That doesn’t tell us what our product will do for you, but it’s reason enough to talk to your doctor or pharmacist first.

• Blood thinners: Korean researchers extracted a small protein fragment (a peptide) from cultured chaga mycelium. In laboratory tests and in mice, it inhibited the clumping of blood platelets (Hyun et al., 2006). Blood thinners also affect blood clotting. So tell your doctor or pharmacist about your chaga use, and let them know before surgery too.
• Blood sugar-lowering medications: animal research has examined the effect of a substance from chaga on blood sugar (Xu et al., 2021). This has not been studied in humans. If you take medication for your blood sugar, consult your GP or pharmacist first.

Does chaga tea have side effects?

Chaga tea has the same considerations as chaga powder because oxalate dissolves in water. With tea made from loose chunks, you also do not know how much chaga you are consuming, and loose chaga is considered a novel food in the EU when sold as a regular foodstuff (European Commission, 2024). That is why we make chaga tea from powder, with the amount measured in grams. Read about how this works in chaga tea made from chaga powder.

Who should be extra cautious with chaga?

Too little research has been done to recommend chaga without consultation for the groups below.

• Kidney problems or a history of kidney stones: consult your GP first because of the oxalate.
• Blood thinners or medications that lower blood sugar: consult your GP or pharmacist first.
• Pregnant or breastfeeding: this has not been studied, so do not use it without consulting your GP or midwife.
• Allergy to mushrooms or fungi: it is best not to use chaga.
• Upcoming surgery: let your doctor know that you use chaga.
• Children: supplements are not intended for children unless your GP advises otherwise.

The product page for our chaga capsules also states: "Do not exceed the recommended daily dose. Consult your doctor before use if you are pregnant, breastfeeding, taking medication, or have a medical condition."

How can you use chaga as wisely as possible?

Use chaga as wisely as possible by sticking to the daily dose on the package, preferably not using multiple chaga products at the same time, and discussing long-term daily use with your GP. For our chaga powder, the recommended dose is 1 to 3 scoops (1 to 3 g) once a day; for our chaga capsules, it is 1 to 3 capsules once a day.

• Follow the packaging. Details for each form are provided in chaga dosage.
• Preferably do not use multiple chaga products at the same time. If you do, add everything together and stay within the daily dosage on the label. Also keep in mind our mushroom complex, which contains 100 mg of chaga extract per capsule.
• Weigh powder in grams instead of using a teaspoon. Read about how to use it in using chaga powder.
• The form makes no difference for oxalate: this applies to powder, capsules, and extract. See also chaga powder or extract.
• If you use chaga every day for an extended period, discuss it with your doctor, especially if you have (had) kidney problems.

Summary in 3 points

• The best-known side effect of chaga is kidney damage caused by oxalate, reported in three people who took chaga powder daily for months to years.
• If you take blood thinners or blood sugar-lowering medication, have (had) kidney problems, or are pregnant, consult your doctor or pharmacist first.
• Follow the daily dosage, preferably do not use multiple chaga products at the same time, and discuss long-term daily use with your doctor.

Frequently asked questions

Is chaga bad for your kidneys?

Chaga contains a lot of oxalate, and there are three reports of severe kidney damage after long-term use of chaga powder. If you have (had) kidney problems or kidney stones, consult your doctor first.

Can chaga cause stomach problems?

This has not been properly studied in humans. Our packaging recommends taking chaga during or shortly after a meal. If you experience symptoms, stop taking it and consult your doctor.

Can I use chaga while pregnant?

This has not been studied. Consult your doctor or midwife.

Can I combine chaga with blood thinners?

This has not been studied in humans. In lab and mouse studies, a substance from chaga inhibited platelet clumping, so consult your doctor or pharmacist first.

Sources

1. Kikuchi Y, Seta K, Ogawa Y, Takayama T, Nagata M, Taguchi T, Yahata K. Case report on oxalate crystals in the kidneys following chaga powder use. Clin Nephrol. 2014;81(6):440-444. doi:10.5414/CN107655. PubMed 23149251
2. Lee S, Lee HY, Park Y, Ko EJ, Ban TH, Chung BH, Lee HS, Yang CW. Case report and literature review of kidney damage after long-term use of chaga. J Korean Med Sci. 2020;35(19):e122. doi:10.3346/jkms.2020.35.e122. PubMed 32419395
3. Kwon O, Kim Y, Paek JH, Park WY, Han S, Sin H, Jin K. Case report of acute oxalate kidney injury caused by chaga powder. Medicine (Baltimore). 2022;101(10):e28997. doi:10.1097/MD.0000000000028997. PubMed 35451393
4. Lee S, Cui S, Fang X, Lee H, Lim SW, Shin YJ, Li C, Yang CW, Chung BH. Animal study of kidney damage in rats after a high dose of chaga. J Korean Med Sci. 2026;41(3):e37. doi:10.3346/jkms.2026.41.e37. PubMed 41555803
5. Hyun KW, Jeong SC, Lee DH, Park JS, Lee JS. Lab study of a peptide from chaga mycelium that inhibited platelet aggregation. Peptides. 2006;27(6):1173-1178. doi:10.1016/j.peptides.2005.10.005. PubMed 16289471
6. Xu T, Li G, Wang X, Lv C, Tian Y. Animal study of a chaga polysaccharide in mice with artificially induced diabetes. BMC Chem. 2021;15(1):64. doi:10.1186/s13065-021-00789-4. PubMed 34920751
7. European Commission. Consultation process on novel food status: Chaga (Inonotus obliquus). Receiving Member State: Finland (Finnish Food Authority). Published November 14, 2024. food.ec.europa.eu (PDF)
8. GOYU, product pages for Organic Chaga Powder and Organic Chaga Capsules 500 mg (directions for use and warning), accessed November 4, 2026.

You can find all forms of our chaga on the buy chaga page.

This article is for informational purposes and is not medical advice. Dietary supplements are not a substitute for a varied and balanced diet and a healthy lifestyle. If in doubt, during pregnancy, or when taking medication, consult your doctor or pharmacist.