Turkey tail passed the test in September: real trials, in people, with a product close to what the research used. Chaga is sold with the same promises (immunity, antioxidants, "the king of mushrooms") and it's everywhere this time of year as a tea or a coffee add-in. So it gets the same test. The answer is very different.
I think of chaga more as a food than a supplement. Where I like it is as one part of a formula, the way you might combine olive leaf, oregano oil and garlic to act on a similar part of your health together. So I wanted to know whether chaga on its own holds up, and whether the formula thinking survives the safety data. (Worth saying: the idea that combinations add potency is itself mostly untested. It's a reasonable instinct, not a trial result.)
Chaga (Inonotus obliquus) isn't really a mushroom in the everyday sense. It's a hard, black, cracked growth (a sclerotium) that forms on birch trees in cold northern forests. It's been used as a folk tea in Russia and Northern Europe for centuries. It grows very slowly, and attempts to grow it in the lab have produced less of the compounds it's studied for (Zheng et al., 2010). So most chaga sold is harvested from the wild.
A PubMed search on 30 September 2026 found no clinical trials or randomised controlled trials of chaga in people. Memorial Sloan Kettering's cancer centre, whose herb database is written for patients and doctors, says the same: "the safety and efficacy of chaga have yet to be evaluated in clinical studies" (MSK, 2023).
What exists is a large laboratory and animal literature: antioxidant, anti-inflammatory, blood-sugar-lowering and anti-tumour effects in cells and rodents (Szychowski et al., 2020; Wang et al., 2025). Even a favourable review concludes that "studies that meet the evidence-based medicine criteria are needed" (Szychowski et al., 2020).
Grade for the immune, antioxidant and anti-cancer claims: mechanistic and untested in people.
That's the same standard I'd apply to a drug. A drug with a big animal literature and no human trials doesn't get prescribed for immunity. Nor should a mushroom get sold for it.
Compared with turkey tail: turkey tail has randomised trials in people with cancer, of a standardised extract. Chaga has none. It isn't a close call.
Chaga is very high in oxalate. Oxalate binds calcium, and in large enough amounts it forms crystals that can block and damage the kidneys. Three case reports describe exactly that:
And in 2026, a Korean team gave rats chaga powder at doses scaled from one of these cases. At the higher dose, the rats developed oxalate crystals in their kidneys and kidney damage (Lee et al., 2026).
What this does and doesn't show. Three case reports don't tell you how common kidney damage is; with no trials, nobody knows. All three involved powder, eaten daily for months, not the occasional cup of tea. But the mechanism is well understood, the animal study reproduces it, and all three people needed dialysis; for one, the damage was permanent. For a product with no proven benefit, that's a poor trade.
The gap that turkey tail passed, between what the research used and what's in the shop, doesn't arise for chaga, because the research wasn't done in people in the first place.
If you still want to use it: an occasional tea rather than daily powder, and don't take it for months at a time. If you've been taking it daily, a routine kidney blood test (creatinine and eGFR) at your GP is a sensible check.
Declared interest. I recommend a small number of practitioner supplement companies to clients. One of them, Amrita, occasionally pays me a small commission, and gives me practitioner pricing on some products that I can pass on to clients as a discount. I use Amrita because it stocks the practitioner brands I was trained on, some of them exclusively in the UK; other stockists can be cheaper. I don’t recommend chaga on its own, though it can appear in combined mushroom products. Clients can buy from anyone. What I’d rather do is help you decide whether you need a mushroom product at all, and if you do, how much and when.
PubMed records resolved and abstracts read 30 September 2026.
Kikuchi Y, et al. Chaga mushroom-induced oxalate nephropathy. Clin Nephrol 2014;81(6):440–444. PMID 23149251. doi:10.5414/CN107655
Kwon O, et al. Chaga mushroom-induced oxalate nephropathy that clinically manifested as nephrotic syndrome: a case report. Medicine (Baltimore) 2022;101(10):e28997. PMID 35451393. doi:10.1097/MD.0000000000028997
Lee S, et al. Development of end stage renal disease after long-term ingestion of chaga mushroom: case report and review of literature. J Korean Med Sci 2020;35(19):e122. PMID 32419395. doi:10.3346/jkms.2020.35.e122
Lee, et al. Kidney injury induced by high-dose chaga mushroom consumption: experimental evidence in a rat model. J Korean Med Sci 2026;41(3):e37. PMID 41555803. doi:10.3346/jkms.2026.41.e37
Memorial Sloan Kettering Cancer Center. About Herbs: Chaga mushroom. Updated 20 February 2023. Accessed 30 Sep 2026.
Szychowski KA, et al. Inonotus obliquus — from folk medicine to clinical use. J Tradit Complement Med 2021;11(4):293–302. PMID 34195023. doi:10.1016/j.jtcme.2020.08.003
Wang Y, et al. Natural products and health care functions of Inonotus obliquus. Curr Issues Mol Biol 2025;47(4). PMID 40699669. doi:10.3390/cimb47040269
Zheng W, et al. Chemical diversity of biologically active metabolites in the sclerotia of Inonotus obliquus and submerged culture strategies for up-regulating their production. Appl Microbiol Biotechnol 2010;87(4):1237–1254. PMID 20532760. doi:10.1007/s00253-010-2682-4 ---