What Are the Side Effects of Mushroom Supplements?

For most adults taking a mushroom supplement at the label dose, the side effects reported in trials are mild and digestive: stomach discomfort, loose stools, wind, headache and allergic reactions.¹ The serious reports belong to a species or a form: kidney failure after daily chaga powder, 3 to 15 g a day, for three months to five years; liver injury with reishi powder; a rash after raw shiitake; heavy metals in raw shilajit resin; and lion's mane reactions described on forums but not in any study.^{2, 4, 5, 6} Do mushroom supplements work? covers every species; lion's mane side effects has its own page.

Sources checked on 29 October 2026.

Is it safe to take mushroom supplements every day?

Within the trial doses, nothing serious was recorded: lion's mane has been taken at 10 g a day for four weeks and about 1 g a day for 49 weeks; reishi at 1.44 g a day for four weeks and 3 g a day for 16 weeks in 84 people; shiitake at 5 or 10 g dried a day for four weeks.^{1, 8, 9, 10} Chaga is the exception: no human trial, and harm on record from about 10 g a day of powder for months.² Stay inside the label dose and do not stack products with the same species.

What side effects have been reported, species by species?

• Lion's mane. The 2025 systematic review lists stomach discomfort, headache and allergic reactions, "commonly unreported"; forum reports of anxiety, panic, low mood, depersonalisation and emotional blunting have no PubMed record (searched 11 October 2026).¹
• Reishi. Three published liver-injury cases with reishi powder, one fatal and one with alcohol.⁴
• Chaga. No human trial. One analysed powder held 14.2 g of oxalate per 100 g, and three cases of kidney failure followed daily powder, 3 to 15 g a day, for three months to five years, one alongside 500 mg of vitamin C a day.^{2, 3, 24} Can chaga be harmful has the cases.
• Cordyceps. No excess adverse events at 3 g a day for 16 weeks.⁹ An add-on to transplant immunosuppressants in China, and a 1996 report found 20,000 ppm lead in a powder that poisoned two people.^{13, 14}
• Shiitake. Cooked, no reported harm at the trial doses above; raw or undercooked, it causes shiitake dermatitis, a streaky itchy rash lasting about ten days (can I eat shiitake every day).^{5, 10}
• Shilajit. Raw resin and some products carry lead, arsenic and mercury: in a 2008 survey, toxic metals in 20.7% of 193 Ayurvedic products bought online, and thallium at up to 0.5 micrograms per gram in 2025.^{6, 7}

Which medicines interact with mushroom supplements?

Known: a human study measured it. Theoretical: a laboratory mechanism. Unstudied: no human data. Never stop a prescribed medicine for a supplement. No mushroom is a "natural blood thinner".

Capsules adding ginkgo or ginseng carry their cautions: ginkgo with anticoagulants and antiplatelets, ginseng with diabetes and blood-pressure medicines, both stopped before surgery; patients asking about rasagiline or sertraline get no answer because nothing has been studied.

Can mushroom supplements affect the liver or kidneys?

The liver signal belongs to reishi powder: three published cases against a four-week trial of 1.44 g a day with liver and kidney markers unchanged.^{4, 8} The one liver case involving lion's mane was a mixed Agaricus blazei and lion's mane powder taken during chemotherapy, which the authors attributed to the Agaricus; none was found for chaga, cordyceps or shilajit.¹¹ The kidney signal belongs to chaga: in the three case reports oxalate crystals blocked the kidneys and all three needed dialysis; no other species has raised creatinine in a trial.^{2, 3, 24}

Who should not take mushroom supplements?

Not without a conversation: kidney disease or kidney stones (chaga); an anticoagulant, antiplatelet or bleeding disorder; insulin or gliclazide; transplant medicines, biologics or an autoimmune condition; surgery booked; and, for lion's mane, a history of panic attacks or depression, or psychiatric medicines. No data at all: pregnancy, breastfeeding and children, because no controlled trial included them. Never: a mushroom allergy.

Can I take a mushroom supplement during cancer or hormone treatment?

Ask your oncology pharmacist first. Some trials of fungal beta-glucans changed immune markers in blood tests, a laboratory finding, not an authorised claim, and no trial has tested these supplements alongside chemotherapy, immunotherapy or hormone treatments.

How do you report a suspected side effect?

To your local authority's trading standards or environmental health team, which works with the Food Standards Agency.¹⁷ Stop, keep the tub for the batch number, and see a pharmacist or GP if symptoms persist; thoughts of self-harm are urgent whatever the cause: NHS 111, your GP, or Samaritans on 116 123.

What we don't know

Whether any mushroom supplement interacts with a prescribed medicine: beyond reishi's clotting and glucose studies, every cell in the table is a mechanism or a blank.^{12, 16} How often side effects occur, since the trials are small and the 2025 review calls them "commonly unreported".¹ What daily use beyond 49 weeks, the longest trial, does.

Frequently asked questions

What are the side effects of a mushroom complex or blend?

A complex or blend carries the cautions of every species in it, each at a fraction of its trial dose; the format, powder, capsule, gummy, tincture or coffee, changes only the amount per serving (what is mushroom powder used for covers tinctures, is mushroom coffee good for you the caffeine). The one placebo-controlled blend trial, 3 g a day of reishi with cordyceps in 84 people for 16 weeks (supplier-funded), recorded no excess adverse events.⁹ A 2026 case report describes seizures and hallucinations in a nine-year-old with epilepsy after escalating doses of a reishi and cordyceps supplement, resolving when it stopped.²¹

Can mushroom supplements cause diarrhoea or constipation?

Loose stools, wind and stomach discomfort are the digestive effects recorded in trials; the 2025 lion's mane review lists stomach discomfort first.¹ A 1998 open-label trial gave 10 healthy adults 4 g of shiitake powder a day in two 10-week runs: in 5 of the 10, eosinophils, a type of white blood cell, rose to four or more times their baseline, 2 had gut symptoms at the same time, and both settled when the powder was stopped.²² No trial has recorded constipation. Sugar-free gummies with more than 10% polyols must carry a laxative warning.²³ Lasting symptoms, or blood in the stool, are a GP matter.

Can you be allergic to one mushroom and not others?

Possibly, since allergy is to specific proteins. Food allergy symptoms are itching or hives, swelling of the lips, face or eyes, wheeze or stomach upset; a swollen throat or tongue or difficulty breathing is anaphylaxis, so call 999.^{19, 20} Raw shiitake's rash is a toxin reaction, not an allergy.⁵

Sources

1. Menon A, et al. Benefits, side effects and uses of Hericium erinaceus. Systematic review, 26 studies. Frontiers in Nutrition, 2025. PubMed 40959699.
2. Lee S, et al. End-stage renal disease after long-term chaga ingestion. Case report. Journal of Korean Medical Science, 2020. PubMed 32419395.
3. Kwon O, et al. Chaga-induced oxalate nephropathy presenting as nephrotic syndrome. Case report. Medicine, 2022. PubMed 35451393.
4. Guedikian R, et al. Reishi-induced acute liver injury with alcohol use. Case report and literature review. Cureus, 2023. PubMed 37885515.
5. Boels D, et al. Shiitake dermatitis, French poison centres 2014 to 2019. Case series. Clinical Toxicology, 2022. PubMed 35404185.
6. Saper RB, et al. Lead, mercury and arsenic in Ayurvedic medicines sold via the internet. Survey of 193 products; US NIH funded. JAMA, 2008. PubMed 18728265.
7. Kamgar E, et al. Thallium in shilajit and its supplements. Laboratory analysis. BMC Chemistry, 2025. PubMed 39827344.
8. Wachtel-Galor S, et al. Lingzhi biomarker responses in a controlled human study. Placebo-controlled crossover trial, 18 adults, 4 weeks. British Journal of Nutrition, 2004. PubMed 14756912.
9. Klupp NL, et al. Ganoderma lucidum for cardiovascular risk factors of metabolic syndrome. Randomised trial, 84 adults, 16 weeks; supplier-funded. Scientific Reports, 2016. PubMed 27511742.
10. Dai X, et al. Daily shiitake and human immunity. Randomised dietary trial, 52 adults, 4 weeks; non-commercial funding. Journal of the American College of Nutrition, 2015. PubMed 25866155.
11. Strobbe G, et al. Grade 3 cytolysis in a cancer patient taking an Agaricus blazei and lion's mane powder. Case report. Journal of Oncology Pharmacy Practice, 2025. PubMed 39223928.
12. Kwok Y, et al. Platelet and haemostatic effects of Ganoderma lucidum in healthy volunteers. Randomised trial, 40 adults, 4 weeks. Anesthesia and Analgesia, 2005. PubMed 16037156.
13. Hong T, et al. Cordyceps sinensis for kidney transplant recipients. Cochrane review. Cochrane Database of Systematic Reviews, 2015. PubMed 26457607.
14. Wu TN, et al. Lead poisoning from contaminated Cordyceps. Two case reports. Science of the Total Environment, 1996. PubMed 8854946.
15. Mori K, et al. Hericenone B and collagen-induced platelet aggregation. Laboratory study. Phytomedicine, 2010. PubMed 20637576.
16. Klupp NL, et al. Ganoderma lucidum for cardiovascular risk factors. Cochrane review, 5 trials, 398 adults; non-commercial funding. Cochrane Database of Systematic Reviews, 2015. PubMed 25686270.
17. Food Standards Agency. How to report a food safety or hygiene issue for members of the public. gov.uk.
18. Hyun KW, et al. Platelet aggregation inhibitory peptide from Inonotus obliquus mycelia. Laboratory and mouse study. Peptides, 2006. PubMed 16289471.
19. NHS. Anaphylaxis (reviewed 21 June 2023). nhs.uk/conditions/anaphylaxis.
20. NHS. Food allergy (reviewed 20 August 2026). nhs.uk/conditions/food-allergy.
21. Melek Arsoy HE, Özdemir Ö. Acute neurotoxicity in a child after a multi-mushroom supplement. Case report. BMC Complementary Medicine and Therapies, 2026. PubMed 42063068.
22. Levy AM, et al. Eosinophilia and gastrointestinal symptoms after ingestion of shiitake mushrooms. Open-label trial, 10 healthy adults, two 10-week runs; publicly funded. Journal of Allergy and Clinical Immunology, 1998. PubMed 9600497.
23. Retained Regulation (EU) No 1169/2011, Annex III, point 2.4 (added polyols above 10%). legislation.gov.uk.
24. Kikuchi Y, et al. Chaga mushroom-induced oxalate nephropathy. Case report. Clinical Nephrology, 2014. PubMed 23149251.
25. Poniedziałek B, et al. Mushroom extracts and human platelet and blood coagulation. In vitro screen of eight edible species on human blood; no external funding. Nutrients, 2019. PubMed 31842490.

Spotted something out of date? Email support@wellgard.co.uk with the page address and the sentence.

General information, not medical advice: if you take a regular medicine or have a health condition, ask your pharmacist or GP first.