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Can Chaga Be Harmful? Kidneys, Medicines and Who Should Avoid It
In this article
- Can chaga be harmful?
- Can chaga cause kidney problems? The oxalate cases
- Who should not take or drink chaga?
- Does chaga interact with blood thinners, diabetes medicines or other prescriptions?
- Is chaga safe in pregnancy, while breastfeeding or for children?
- Does chaga affect the liver, blood pressure, hormones or sleep?
- How much chaga is safe?
- What should you do if chaga makes you unwell?
- What we don't know
- Frequently asked questions
Chaga can be harmful in one documented way: it is extremely high in oxalate (14.2 g per 100 g in one analysed powder), and three published cases of kidney failure, all needing dialysis, followed daily chaga powder, 3 to 15 g a day, taken for three months to five years, one in a man also taking 500 mg of vitamin C a day.1, 2, 3 No human trial has tested chaga for any outcome, so beyond the kidney cases its side effects are unstudied rather than known to be absent. People with kidney disease or a history of kidney stones should not take chaga without medical advice; nobody should take high-dose vitamin C with it; and anyone on anticoagulants, diabetes medicines, immunosuppressants or cancer treatment should ask a pharmacist first, because none of those combinations has been studied. Pregnancy, breastfeeding and children: no data, so not recommended. This is the chaga safety page; the evidence for every mushroom supplement, species by species, is in do mushroom supplements work.
Sources checked on 29 October 2026.
Can chaga be harmful?
Yes, at high daily doses over time, through its oxalate. Chaga's main organic acid is oxalic acid, and the powder analysed in the 2020 Korean case held 14.2 g of oxalate per 100 g.2, 4 In large sustained amounts oxalate forms calcium oxalate crystals in the kidney tubules, which is what all three biopsies showed.1, 2, 3 Short of that, chaga has not been studied in people, so there is no trial list of common side effects; what people report online (stomach upset, loose stools, headaches, feeling tired or wired) is unverified.
Can chaga cause kidney problems? The oxalate cases
Three cases are published.
- 2014, Japan. A 72-year-old woman with liver cancer took chaga powder, 4 to 5 teaspoons a day, for six months. She needed haemodialysis; the biopsy showed oxalate crystals in the tubules and scarring. It was the first reported case.1
- 2020, Korea. A 49-year-old man reached end-stage kidney disease, and long-term dialysis, after five years of chaga powder for severe eczema: 3 g a day for four years, then 9 g a day for a year. His remaining powder held 14.2 g of oxalate per 100 g (two other commercial powders tested at 2.8 and 11.2 g), 2
- 2022, Korea. A 69-year-old man took 10 to 15 g of chaga powder a day plus 500 mg of vitamin C a day for three months and developed acute kidney injury with heavy protein loss; calcium oxalate crystals filled the tubules. He needed dialysis and steroids, and recovered over a month.3
In 2026 the Korean group fed rats chaga powder at doses extrapolated from one of these cases and found crystal deposits, tubular injury and protein in the urine at the higher dose, which ties the human cases to a mechanism.6 Warning signs to act on: pain in the side or lower back, blood in the urine, swollen ankles, feet or hands, feeling sick or unexplained tiredness. Stop the chaga and see a GP, and mention it, because few doctors will think to ask.5, 10
Who should not take or drink chaga?
Without medical advice: anyone with chronic kidney disease or a single kidney; anyone who has ever had a kidney stone; anyone with a bowel condition that raises oxalate absorption, such as Crohn's disease, ulcerative colitis, coeliac disease or previous bowel or weight-loss surgery; and anyone taking high-dose vitamin C, because part of a vitamin C dose is converted to oxalate: 1,000 mg twice a day raised urinary oxalate in 40% of 48 adults in a controlled crossover study.2, 10, 11 Not at all, because there is no safety data: pregnant and breastfeeding women, children and teenagers. With a pharmacist or clinic conversation first: anyone on the medicines in the table below. Anyone with a mushroom allergy should avoid chaga as they would any fungus.8
Does chaga interact with blood thinners, diabetes medicines or other prescriptions?
No interaction between chaga and any medicine has been studied in people, so every row below is theoretical or unstudied; tell the pharmacist or clinic, and never stop a prescribed medicine on your own.
| Medicine group | What is known for chaga | What to do |
|---|---|---|
| Anticoagulants (warfarin, apixaban, rivaroxaban, edoxaban, dabigatran) and antiplatelets (aspirin, clopidogrel) | Theoretical. A laboratory peptide from chaga mycelium blocked platelet clumping in a test tube and in mice; no human bleeding data, so "chaga is a blood thinner" has no trial behind it in either direction.13 | Tell the anticoagulant clinic or pharmacist; report unusual bruising or bleeding. |
| Diabetes medicines (insulin, gliclazide, metformin and others) | Theoretical. Extracts lowered glucose in diabetic mice; no human study.12 | Tell the diabetes team; check glucose more often for a fortnight; never adjust a dose yourself. |
| Immunosuppressants (ciclosporin, tacrolimus, mycophenolate) and biologics | Theoretical. Mushroom polysaccharides change immune markers in the laboratory; a transplant patient also has a kidney to protect. | Avoid unless the transplant or rheumatology team agrees. |
| Chemotherapy, immunotherapy and hormone therapies for cancer | Unstudied. The first kidney case was a cancer patient taking chaga alongside her care. | Tell the oncology team before taking any mushroom product. |
| Levodopa, MAO-B inhibitors, antidepressants, ADHD stimulants, HRT and the pill | Unstudied for chaga. | Mention it at your next review; stop and seek advice if anything changes. |
| High-dose vitamin C supplements | Documented co-factor: 500 mg a day in the third kidney case.3, 11 | Do not combine; vitamin C from food is fine.7 |
| Surgery | Unstudied. | Stop chaga and tell the pre-operative team, as with any supplement. |
The cross-species table covering lion's mane, reishi, cordyceps and shilajit is on what are the side effects of mushroom supplements.
Is chaga safe in pregnancy, while breastfeeding or for children?
No trial of chaga, or of any mushroom supplement, has included pregnant or breastfeeding women or children, and the oxalate load is a specific reason for caution in pregnancy. Not recommended in any of these groups.
Does chaga affect the liver, blood pressure, hormones or sleep?
Liver: no published case of liver injury from chaga was found in a PubMed search on 29 October 2026 (unlike reishi powder, which has three), and no human study has measured liver enzymes on chaga; "detox" is not a measurable outcome. As with any supplement, dark urine, pale stools, yellowing skin or eyes or severe tiredness mean stop and see a GP. Blood pressure: no human study in either direction. Hormones: no human study has measured testosterone, oestrogen, cortisol or thyroid hormones on chaga. Sleep: caffeine-free, no trial; a racing heart or feeling wired after chaga has no known mechanism, so if it happens, stop and consider what else changed.
How much chaga is safe?
No trial dose exists, so no one can give a tested safe amount. The amounts that caused harm were 3 to 15 g of raw powder a day, taken daily for three months to five years, and the lowest of them, 3 g a day for four years, is the serving many UK chaga powders state on the label.1, 2, 3 An extract does not hold the same oxalate as raw ground chaga, but published oxalate figures for extracts are scarce, so no label serving can be called safe on the evidence; keep to the label, do not add vitamin C, and take breaks from daily use. Daily drinking, brewing and amounts per cup are on can you drink chaga tea every day; what chaga has and has not been tested for is on what is chaga good for.
What should you do if chaga makes you unwell?
Stop taking it. For mild symptoms, speak to a pharmacist or your GP; for the kidney warning signs above, or any severe or persistent symptom, contact your GP the same day or call NHS 111. Report the reaction to your local authority's trading standards or environmental health team, which works with the Food Standards Agency.9 The three chaga kidney cases are known only because clinicians wrote them up.1, 2, 3 Take the packaging to any appointment.
What we don't know
No trial has given chaga to people, so there is no measured rate of any side effect, no tested dose and no safe upper limit.1, 2, 3 Nobody has published the oxalate content of a chaga extract powder or a brewed tea, and the three powders that have been measured ranged from 2.8 to 14.2 g per 100 g, so the oxalate in a UK label serving cannot be calculated.2 No interaction with any medicine has been studied, and three case reports cannot show how often harm occurs among the many people who drink chaga without incident.
Frequently asked questions
Can you mix chaga with ashwagandha?
No study has looked at the combination. Ashwagandha carries its own cautions and chaga the oxalate one; taking both means carrying both.
Is chaga high in iron?
No reliable analysis gives an iron figure for brewed chaga or a 3 g extract, so chaga is not a source of iron to count on.
Is chaga hard on the liver?
No human study has measured liver enzymes on chaga and no published case of liver injury from chaga was found in a PubMed search on 29 October 2026; the mushroom with liver cases is reishi powder, and chaga's documented organ harm is to the kidneys.
Is it safe to take chaga every day?
Nobody has tested it. The harm on record came from daily powder, 3 to 15 g a day, over months to years, so if you take it daily keep to the label, avoid vitamin C supplements, take breaks, and skip it altogether with kidney disease or stones.
Sources
- Kikuchi Y, et al. Chaga mushroom-induced oxalate nephropathy. Case report, 1 patient. Clinical Nephrology, 2014. PubMed 23149251.
- Lee S, et al. End stage renal disease after long-term ingestion of chaga mushroom. Case report and literature review, 1 patient; no conflicts declared. Journal of Korean Medical Science, 2020. PubMed 32419395.
- Kwon O, et al. Chaga mushroom-induced oxalate nephropathy manifesting as nephrotic syndrome. Case report, 1 patient; no conflicts declared. Medicine, 2022. PubMed 35451393.
- Glamočlija J, et al. Chemical characterization and biological activity of chaga. Laboratory analysis of extracts; publicly funded. Journal of Ethnopharmacology, 2015. PubMed 25576897.
- NHS. Kidney stones. Reviewed 17 September 2026. nhs.uk.
- Lee S, et al. Kidney injury induced by high-dose chaga mushroom consumption. Rat study, three groups; no conflicts declared. Journal of Korean Medical Science, 2026. PubMed 41555803.
- NHS. Vitamin C. Reviewed 3 August 2020. nhs.uk.
- NHS. Allergies. Reviewed 5 March 2026. nhs.uk.
- Food Standards Agency. How to report a food safety or hygiene issue for members of the public. gov.uk.
- NHS. Chronic kidney disease. Reviewed 22 March 2023. nhs.uk.
- Massey LK, et al. Ascorbate increases human oxaluria and kidney stone risk. Randomised crossover study, 48 adults. Journal of Nutrition, 2005. PubMed 15987848.
- Szychowski KA, et al. Inonotus obliquus: from folk medicine to clinical use. Narrative review; no conflicts declared. Journal of Traditional and Complementary Medicine, 2021. PubMed 34195023.
- Hyun KW, et al. Platelet aggregation inhibitory peptide from Inonotus obliquus mycelia. Laboratory and mouse study; publicly funded. Peptides, 2006. PubMed 16289471.
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