Who Shouldn’t Take Reishi? Side Effects, Interactions and Safety — What the Trials Actually Recorded

In brief5 points · 1-minute read

• Across the randomized trials, daily amounts of 0.72 to 3 g over as long as 16 weeks produced only mild, infrequent side effects.
• Recorded side effects are mild: a dry mouth, some dizziness, stomach upset, itching and occasional insomnia; 9.1% of 1,374 surveyed users reported one.
• Liver injury rests on three case reports involving mushroom powder, while trials measuring liver enzymes over 84 days, over 16 weeks and over six months found no rise.
• A 1990 study saw platelet inhibition, a 2005 randomized trial of 40 volunteers did not; with anticoagulants ask a physician first and pause two weeks before surgery.
• Pregnant or breastfeeding women, children, and people on immunosuppressants or with liver disease should not use it without medical advice.

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Reishi (Ganoderma lucidum, lingzhi in Chinese medicine, mannentake in Japan) is the most-studied medicinal mushroom for safety — and also the one with the most confident warnings online: “thins the blood,” “damages the liver,” “lowers blood pressure.” Most of those warnings trace back to a single source each. This page separates what controlled trials recorded from what case reports describe: in the trials, reishi was well tolerated at 0.72 to 3 grams a day for up to 16 weeks, with mild side effects — dry mouth, mild dizziness, digestive discomfort, occasional insomnia — and no liver or blood toxicity. Alongside that sit three published liver case reports, one platelet study from 1990 that a later trial did not reproduce, a laboratory study on drug-metabolism enzymes, and no pregnancy data at all. We grow and sell reishi. That is exactly why every claim below carries a PubMed link.

Does reishi have side effects?

Yes — mild ones, and rarely. In the controlled trials the side effects recorded were dry mouth and throat, mild dizziness, digestive discomfort, itching or rash, and in one trial insomnia; none of the trials reported a serious adverse event, and the ones that measured liver and kidney markers found no change. The rare serious events in the literature are case reports, almost all involving raw mushroom powder, and they are described in full below.

That is the sentence most safety pages stop at. The problem is that “rarely” means different things depending on where you look. In a 10-day trial of 16 healthy volunteers taking 2 g of extract twice a day, with electrocardiograms, blood counts, chemistry and urinalysis, the authors reported no adverse effects compared with placebo. In a survey of 1,374 cancer patients who had been using reishi products for months or years, 125 people — 9.1% — reported an adverse effect. Both are true. The first tells you what a defined dose of a defined extract does over a defined period in healthy people; the second tells you what a population of patients on many other treatments, taking many different reishi products, notices and attributes. This page keeps the two apart, because the honest answer to “what will happen to me” depends on which of those two situations you are in.

What did the controlled trials actually record about safety?

Every randomized reishi trial we could find that reported safety data is in the table below — with the dose, the duration, what was measured, and what was found. The pattern is consistent: mild, infrequent side effects, and no signal in blood counts, liver enzymes or kidney markers at doses up to 3 g a day for up to 16 weeks.

Three things to read off this table. First, the doses: the trials used between 0.72 and 3 g of reishi a day, and one trial arm went as high as 11.2 g — a daily tincture dose of about 1.4 ml delivers far less material than any of them, and we say so plainly on the dosage page rather than converting. Second, the longest controlled exposure is six months; beyond that, the honest statement from a 2021 critical review is that data on chronic use, teratogenicity and genotoxicity “are missing for Reishi.” Third, most of these trials were built to test efficacy, and safety was a secondary record — which is why the case reports below matter more than their number suggests.

What do people report outside the trials?

The best real-world data comes from a 2024 cross-sectional survey of 1,374 cancer patients in China using reishi products: 125 of them (9.1%) reported at least one adverse effect. The five most common were dry mouth (5%), constipation (4%), insomnia (3%), itching (3%) and vertigo (3%). More than half of respondents also reported that nausea, fatigue and poor appetite improved — but this is a survey of users, not a controlled comparison, so both the benefits and the harms are self-attributed.

Two features of that survey are worth holding on to. The adverse effects it found are the same mild ones the trials recorded — nothing new appeared once thousands of people were asked. And the population was cancer patients, mostly on other treatments and often on other herbs, which is the population where reishi is most used and where interactions matter most. A second real-world source is pharmacovigilance: a 2025 analysis of the World Health Organization’s VigiBase found that among 7,856 reports naming a single natural product as the sole suspect, 15.8% were serious, and reishi was among the products most frequently associated with serious reports — with the authors stating plainly that “causality remained unclear due to insufficient data.” We include that sentence because leaving it out would be the kind of omission this page exists to avoid: a reporting database counts reports, not proof, and reishi is one of the most widely consumed products in the set.

Does reishi damage the liver? What the three case reports actually say

Three published case reports link reishi to liver injury, and every warning you have read comes from them. In 2004, a letter in the Journal of Hepatology described hepatotoxicity from “a formulation” of lingzhi in Hong Kong. In 2005, a Thai patient died of fulminant hepatitis after taking lingzhi mushroom powder; the 2007 report notes that both patients had previously taken traditionally boiled lingzhi without toxic effect and switched to powder one to two months before the episode, and both were taking other agents. In 2023, a 47-year-old man developed acute hepatitis after taking reishi powder together with alcohol; his symptoms and laboratory values resolved completely within two weeks.

Now the other side of the ledger, which the warnings never quote. The 84-day beta-glucan trial measured liver and kidney markers and found no significant change. The 16-week trial at 3 g a day found no increased risk of adverse events. The six-month crossover found liver enzymes going down, not up. The 12-week trial in children found no rise in aminotransferases. The Cochrane review found no hepatological toxicity in any of five trials, and the 2025 meta-analysis of 17 trials found no effect on liver enzymes at all. So the picture is: rare, idiosyncratic, and — in the two best-documented cases — tied to a change of product form and to the presence of other agents (alcohol, other drugs). What we take from it is practical, not dismissive: if you have liver disease, elevated liver enzymes, or drink heavily, do not start reishi without your physician — and if you develop dark urine, yellowing of the eyes, or right-upper abdominal pain on any supplement, stop it and get tested. Our extract is an alcohol tincture; the daily amount is measured in drops, but that is one more reason the liver section belongs at the top of this page and not at the bottom.

Does reishi thin the blood — and what does the 1990 study really show?

Two human studies answer this question, and they disagree. In 1990, a Chinese study found that a water-soluble reishi extract inhibited platelet aggregation in vitro in a dose-dependent way, and that patients with atherosclerotic disease who took 1 g three times daily for two weeks showed maximum inhibition of ADP-induced aggregation of 31.49% and 17.7%. In 2005, a randomized, double-blind trial gave 40 healthy volunteers 1.5 g of reishi a day for four weeks and measured a full coagulation screen, fibrinogen, von Willebrand activity, platelet function and thromboelastography at four and eight weeks: no significant differences from placebo, all values within the normal range.

The 1990 finding is real and mechanistically plausible — adenosine, a known platelet inhibitor, was isolated from reishi in 1985 — and it is the reason our own general side-effects guide tells readers to stop reishi two weeks before surgery. The 2005 trial is the better-designed study, and its authors concluded that pre-operative reishi “is unlikely to increase the risk of surgical bleeding in otherwise healthy patients.” Both can be right: the 1990 patients had vascular disease and took 3 g a day of a water extract; the 2005 volunteers were healthy and took half that. What neither study tested is the situation that actually matters — a person already on warfarin, apixaban, rivaroxaban, clopidogrel or daily aspirin, adding reishi on top. For that person there is no trial, only mechanism, and mechanism is enough for a rule: ask the prescribing physician before starting, and if you do start, tell them so INR or bleeding can be watched. We keep the two-week pre-surgery rule as a precaution we can defend, not as a finding we can cite.

Does reishi lower blood pressure or blood sugar?

Less than the warnings imply. The 12-week crossover trial in people with borderline hypertension found no change in blood pressure. The 2025 meta-analysis of 17 trials found no effect on blood pressure, fasting glucose or lipid profile — only a small drop in heart rate, about four beats a minute. The 16-week trial in people with type 2 diabetes found no effect on HbA1c or fasting glucose at 3 g a day, and the 2015 Cochrane review of cardiovascular risk factors reached the same conclusion.

This matters for the interaction question. “Reishi may lower blood sugar, so diabetics should beware” is the standard line, and it comes from animal studies; the largest human trial built specifically to test glucose-lowering in diabetics found nothing. The 12-week crossover did find lower fasting insulin and insulin resistance, which is a mild metabolic effect, not a hypoglycaemia risk. So the fair statement is: if you take insulin or a sulfonylurea, monitor as you always do and tell your physician about any supplement — but the evidence does not support the idea that reishi will push your sugar down. For blood pressure, the one measured effect is a slightly slower heart rate; if you already have a low resting heart rate or take a beta-blocker, that is worth a conversation, and mild dizziness (recorded in the trials and in the survey as vertigo, 3%) is the symptom to watch.

Which medications interact with reishi?

No human interaction trial exists for reishi, so every interaction on this list is either mechanistic or precautionary. The mechanistic one is new: a 2024 laboratory study screened 66 reishi triterpenoids against the cytochrome P450 enzymes that metabolise most drugs and found that a dichloromethane extract inhibited several of them in vitro, altered the pharmacokinetics of four drugs in rats, and that two compounds interfered with the metabolism of 16 drugs in the test tube. That is a signal, not a clinical finding — but it is the reason we say “tell your physician” rather than “it’s just a mushroom.”

Our general guide to medicinal mushrooms and drug interactions covers the other species; this table is reishi only, and it is deliberately short on adjectives. Where the row says “no trial,” that is the finding.

Is reishi safe in pregnancy or breastfeeding?

Nobody knows, because no trial has ever included pregnant or breastfeeding women. The only pregnancy data are in rodents. Our position is the same as for every medicinal mushroom, and we wrote a full page on it: not now — not because of a known harm, but because “no data” is not the same as “safe,” and an alcohol tincture is the wrong vehicle in any case.

The 2021 critical review that surveyed the whole reishi literature said it in one line: studies on “chronic use, teratogenicity, mutagenicity, and genotoxicity are missing for Reishi.” That is not an alarming sentence; it is an empty one, and the correct response to an empty sentence in pregnancy is to wait. If a practitioner has advised reishi during pregnancy, the question to bring back to them is which study they are relying on — because we could not find one.

Can children take reishi?

The best evidence is a 12-week randomized trial in 3- to 5-year-olds in Colombia, who ate a yogurt enriched with reishi beta-glucans: the intervention was “safe and well tolerated,” with no rise in creatinine or liver enzymes and adherence above 90%. That is reassuring about the beta-glucan itself — and irrelevant to an alcohol-based tincture, which we do not offer for children.

The distinction is product form again. A beta-glucan stirred into yogurt and a triple-extracted alcohol tincture measured in drops are different things, and the trial says nothing about the second. Our page on medicinal mushrooms for children lays out what has been studied and why the decision belongs to a paediatrician; the short version for reishi is that the safety data in children exists only for a food, not for our product, and we will not fill that gap with a dose we invented.

Can you be allergic to reishi?

Yes, and the mechanism is not mysterious: reishi is a fungus, and Ganoderma spores are a recognised airborne allergen. In a skin-prick study of 33 allergic patients in a tropical climate, 30% reacted to spore extract of a related Ganoderma species, and among asthmatics the figure was 44% — as high as house-dust mite. In the reishi user survey, itching was reported by 3%; in a 2024 trial of a reishi-derived immunomodulatory peptide, one participant with asthma developed a skin rash on day 15 and left the study.

What this means for you: if you have a known mould allergy, asthma triggered by damp environments, or a history of reacting to mushrooms as food, start with a very small amount and watch the skin and the breathing for the first days. Itching, hives, wheeze or facial swelling are the signs to stop on. A separate, stranger finding belongs here too: a 2006 Thai case report described a lymphoma patient with chronic watery diarrhoea whose stool was full of Ganoderma spores from a powdered lingzhi supplement — spores that “must be differentiated from intestinal helminth ova,” and which disappeared, with the diarrhoea, once he stopped. Spore-heavy powders are a different product from a fruiting-body extract, but it is one more reason we keep repeating which product a finding is about.

Reishi and insomnia — the irony nobody expects

Reishi is sold as the “calming” mushroom, yet insomnia is one of the few side effects that shows up in both the trials and the survey: the Cochrane review lists it alongside nausea as the only recorded side effects in one trial, and 3% of surveyed users reported it. Reishi is not a sedative — no human trial has shown it to be — and in some people it seems to do the opposite.

We cover the sleep evidence honestly on the reishi for sleep page and the stress evidence, trial by trial, on reishi for stress and anxiety. For the safety question the practical advice is simple: the tradition is to take reishi in the evening, and most people do; if you find yourself more alert rather than less, move the dose to the morning for a week and compare. Dry mouth, the most common complaint in the survey at 5%, is the other one to know about in advance — it is harmless and answered with a glass of water, but it surprises people who were promised only calm.

Digestive side effects — and the “detox reaction” that no trial measured

Mild digestive discomfort — bloating, loose stool, occasionally constipation (4% in the survey) — is the most ordinary reishi side effect and the easiest to manage: start at a low dose and increase over one to three weeks, as the dosage guide describes. What no trial has ever measured is a “detox reaction” or “healing crisis”; if a supplement makes you feel worse, the evidence-based reading is that the dose is too high or the product does not suit you, not that toxins are leaving.

We say this against our own commercial interest, because “it’s the detox working” is the most convenient sentence a seller can offer a customer who feels unwell. The controlled trials give us a better sentence: at study doses, reishi produced mild effects in a minority and nothing serious — so a strong reaction is information, and the right response is to reduce or stop, not to push through. If nausea or diarrhoea persists for more than a few days at the lowest dose, that particular bottle is not for you, and our 100-day trial period exists precisely so that this costs you nothing.

Why the product matters more than the mushroom: what is actually in your bottle

Most of the serious reports above involve powders and spore preparations, and a 2017 study of 19 reishi supplements sold in the United States found that only five — 26.3% — contained what their labels claimed. A safety page that does not ask “which reishi?” is answering the wrong question. Our answer is a test report, not an adjective: the reishi extract’s beta-glucan is measured at 25.65% on a dry basis, starch (alpha-glucan) is not detected, and the purity screens are open.

We print the cadmium value rather than writing “trace” because a number is checkable and an adjective is not; the full reports are open, and how to read a test report walks through them line by line. The point for safety is narrow and important: heavy-metal contamination and undeclared fillers are the risks a buyer can actually eliminate — not by choosing a different mushroom, but by choosing a product whose contents were measured. Fresh fruiting body from our farm, an extraction ratio of 1:3, seven weeks in alcohol, and a lab report per extract: that is the whole of our safety claim about the product itself. What reishi does in your body at that dose, the trials above describe better than we can.

Who should not take reishi — the list

Some of these are findings, most are precautions, and we label which is which. Without a physician’s explicit go-ahead, reishi is not for: people on anticoagulants or antiplatelet drugs; people on immunosuppressants or in active oncology treatment; people with liver disease or elevated liver enzymes; anyone pregnant or breastfeeding; children (not with an alcohol tincture); and anyone with a known allergy to mushrooms or moulds.

If none of these applies, the trials’ answer is the one at the top of this page: mild, infrequent side effects, no organ toxicity at study doses, and the first two weeks at a low dose will tell you whether dry mouth, digestive discomfort or wakefulness are going to be your particular experience. If you are not sure reishi is even the right mushroom for your goal, “Which mushroom is right for me” answers that before you spend anything, and the matching quiz does it in two minutes.

What this page does not claim

We do not claim reishi is “completely safe” — the case reports are real. We do not claim it is dangerous — the trials are also real, and larger. We do not claim our extract was tested for safety in a trial; the trials used powders, capsules and isolated beta-glucan, and our lab report measures what is in the bottle, not what it does. And we do not convert study doses into drops, because no study tested drops.

Two things we would like to see, and cannot offer: a human trial of reishi in people on anticoagulants, and any human data in pregnancy. Until they exist, the honest safety page is a list of precautions with the evidence grade written next to each — which is what this one tries to be. Our lion’s mane safety page is built the same way, and the general guide to side effects of medicinal mushrooms covers cordyceps, turkey tail and the rest.

The bottom line

In controlled trials of up to 132 people and up to 16 weeks, reishi was well tolerated at 0.72 to 3 g a day, with mild side effects — dry mouth, mild dizziness, digestive discomfort, occasional insomnia — and no toxicity to blood, liver or kidneys. Outside the trials, 9.1% of 1,374 long-term users reported an adverse effect, all of them mild. The serious reports are three liver case reports involving powders and other agents, one 1990 platelet study that a better 2005 trial did not reproduce, and a laboratory signal on drug-metabolising enzymes. That evidence supports precautions, not alarm: anticoagulants, immunosuppressants, active oncology treatment, liver disease, pregnancy, children and mould allergy are the situations where reishi waits for a physician. For everyone else, the risk the evidence actually identifies is a product that does not contain what its label says — and that one is checkable.

Frequently asked questions

What are the most common side effects of reishi?

In the controlled trials: dry mouth and throat, mild dizziness, digestive discomfort, itching or rash, and in one trial insomnia. In a survey of 1,374 long-term users, 9.1% reported an adverse effect — dry mouth 5%, constipation 4%, insomnia 3%, itching 3%, vertigo 3%. No trial reported a serious adverse event.

Can reishi cause liver damage?

Three case reports link reishi to liver injury — Hong Kong 2004, a fatal case in Thailand 2005, and a 2023 case with alcohol that resolved in two weeks — all involving mushroom powder, two after switching from traditional decoction. Trials of 84 days, 16 weeks and six months that measured liver enzymes found no rise. With liver disease or heavy alcohol use, do not start without a physician.

Does reishi thin the blood?

A 1990 study found platelet inhibition in patients taking 1 g three times daily for two weeks; a 2005 randomized trial of 40 healthy volunteers at 1.5 g a day for four weeks found no change in any coagulation or platelet measure. No trial has tested reishi in people on anticoagulants, so our rule is: ask the prescriber first, and stop two weeks before surgery.

Can I take reishi with blood-pressure or diabetes medication?

The evidence shows less effect than the warnings suggest: no blood-pressure change in a 12-week crossover or in a meta-analysis of 17 trials, and no effect on HbA1c or fasting glucose in a 16-week trial at 3 g a day. The one measured effect is a heart rate about four beats a minute lower. Monitor as usual and tell your physician.

Is reishi safe during pregnancy?

No trial has ever included pregnant or breastfeeding women; the only data are in rodents, and a 2021 review states that teratogenicity and chronic-use studies “are missing for Reishi.” Our position is not now — no data is not the same as safe, and an alcohol tincture is the wrong vehicle regardless.

Why does reishi keep me awake?

Insomnia appears in both the trials (one trial recorded it alongside nausea) and the user survey (3%). Reishi is not a sedative, and in some people it is mildly activating. If that is you, move the dose to the morning for a week and compare.

Can I be allergic to reishi?

Yes. Ganoderma spores are a documented airborne allergen — 30% of allergic patients and 44% of asthmatics reacted to a related species in a skin-prick study — and itching was reported by 3% of users. With a mould or mushroom allergy, start with a very small amount and stop on itching, hives, wheeze or swelling.

How long can I take reishi continuously?

The longest controlled exposure is six months (42 healthy adults, no adverse events), and the longest at a full dose is 16 weeks at 3 g a day. Beyond that there is no controlled data; the 2021 critical review lists chronic-use safety as a gap. Within that window, the trials found no cumulative toxicity.

Scientific sources (peer-reviewed)

• Reishi — 10 days in 16 healthy volunteers, 2 g extract twice daily: no adverse effects vs placebo (ECG, blood counts, chemistry, urinalysis) — Wicks SM, Tong R, Wang CZ, et al. The American Journal of Chinese Medicine, 2007;35(3):407-414. View on PubMed
• Reishi — single 1.1 g dose and 10 days at 0.72 g/day in 10 volunteers: no deleterious effects on measured variables — Wachtel-Galor S, Szeto YT, Tomlinson B, Benzie IF. International Journal of Food Sciences and Nutrition, 2004;55(1):75-83. View on PubMed
• Reishi — 40 healthy volunteers, 1.5 g/day for 4 weeks: no impairment of platelet function or coagulation at 4 and 8 weeks — Kwok Y, Ng KFJ, Li CCF, Lam CCK, Man RYK. Anesthesia & Analgesia, 2005;101(2):423-426. View on PubMed
• Reishi — platelet aggregation inhibited in vitro (dose-dependent) and in 33 atherosclerotic patients after 1 g three times daily for 2 weeks (maximum inhibition 31.49% and 17.7%) — Tao J, Feng KY. Journal of Tongji Medical University, 1990;10(4):240-243. View on PubMed
• Reishi — isolation of a platelet-aggregation inhibitor (adenosine) from the fruiting body — Shimizu A, Yano T, Saito Y, Inada Y. Chemical & Pharmaceutical Bulletin, 1985;33(7):3012-3015. View on PubMed
• Reishi — 132 adults with neurasthenia, 1,800 mg three times daily for 8 weeks: “well tolerated” — Tang W, Gao Y, Chen G, et al. Journal of Medicinal Food, 2005;8(1):53-58. View on PubMed
• Reishi — 26 adults with borderline blood pressure or cholesterol, 1.44 g/day for 12 weeks (crossover): well tolerated; no change in blood pressure or BMI; lower fasting insulin — Chu TT, Benzie IF, Lam CW, et al. British Journal of Nutrition, 2012;107(7):1017-1027. View on PubMed
• Reishi — 84 adults with type 2 diabetes and metabolic syndrome, 3 g/day for 16 weeks: no effect on HbA1c or fasting glucose; no overall increased risk of adverse events — Klupp NL, Kiat H, Bensoussan A, Steiner GZ, Chang DH. Scientific Reports, 2016;6:29540. View on PubMed
• Reishi — Cochrane review of cardiovascular risk factors: 5 trials, 398 participants, 1.4–3 g/day over 12–16 weeks; no significant effect on HbA1c, cholesterol or BMI — Klupp NL, Chang D, Hawke F, et al. Cochrane Database of Systematic Reviews, 2015;2015(2):CD007259. View on PubMed
• Reishi — Cochrane review of cancer treatment: 5 randomized trials; one recorded nausea and insomnia; no significant haematological or hepatological toxicity; CD3, CD4 and CD8 raised by 3.91%, 3.05% and 2.02% — Jin X, Ruiz Beguerie J, Sze DM, Chan GC. Cochrane Database of Systematic Reviews, 2016;4(4):CD007731. View on PubMed
• Reishi — beta-glucan for 84 days in healthy adults 18–55: no significant change in liver or kidney function markers — Chen SN, Nan FH, Liu MW, et al. Foods, 2023;12(3):659. View on PubMed
• Reishi — 42 healthy adults, 225 mg enriched capsule for six months (crossover): liver enzymes GOT and GPT reduced 42% and 27%; mild fatty liver reversed on ultrasound — Chiu HF, Fu HY, Lu YY, et al. Pharmaceutical Biology, 2017;55(1):1041-1046. View on PubMed
• Reishi spore powder — 42 adults with Alzheimer’s disease, 6 weeks: all adverse events mild, no difference from placebo; no efficacy — Wang GH, Wang LH, Wang C, Qin LH. Medicine, 2018;97(19):e0636. View on PubMed
• Reishi spore powder — 48 breast-cancer patients on endocrine therapy, 4 weeks: liver and kidney function measured; no serious adverse effects — Zhao H, Zhang Q, Zhao L, et al. Evidence-Based Complementary and Alternative Medicine, 2012;2012:809614. View on PubMed
• Reishi — cross-sectional survey of 1,374 cancer patients using reishi: 125 (9.1%) reported adverse effects — dry mouth 5%, constipation 4%, insomnia 3%, pruritus 3%, vertigo 3% — Li X, Sun L, Chimonas S, et al. Integrative Medicine Research, 2024;13(4):101089. View on PubMed
• Reishi-derived immunomodulatory peptide — 19 breast-cancer patients, 6 months: one participant with asthma developed a skin rash on day 15; no other adverse events — Su YW, Huang WY, Lin SH, et al. Integrative Cancer Therapies, 2024;23:15347354241242120. View on PubMed
• Case report — hepatotoxicity due to a formulation of lingzhi (Hong Kong) — Yuen MF, Ip P, Ng WK, Lai CL. Journal of Hepatology, 2004;41(4):686-687. View on PubMed
• Case report — fatal fulminant hepatitis associated with lingzhi mushroom powder, after switching from traditionally boiled lingzhi; other agents also taken — Wanmuang H, Leopairut J, Kositchaiwat C, Wananukul W, Bunyaratvej S. Journal of the Medical Association of Thailand, 2007;90(1):179-181. View on PubMed
• Case report — acute liver injury in a 47-year-old man after reishi powder with alcohol; complete resolution within two weeks — Guedikian R, Kim B, Singh G, et al. Cureus, 2023;15(9):e45953. View on PubMed
• Case report — chronic watery diarrhoea with Ganoderma spores in the stool (pseudoparasitosis) in a lymphoma patient taking powdered lingzhi; resolved on stopping — Wanachiwanawin D, Piankijagum A, Chaiprasert A, et al. Southeast Asian Journal of Tropical Medicine and Public Health, 2006;37(6):1099-1102. View on PubMed
• Mechanism — reishi triterpenoids inhibit cytochrome P450 enzymes in vitro and alter the pharmacokinetics of drugs in rats; two compounds interfered with the metabolism of 16 drugs — Li D, Lin Y, Lv X, et al. Frontiers in Pharmacology, 2024;15:1485209. View on PubMed
• Meta-analysis — 17 randomized trials, 971 participants, 200–11,200 mg/day for 1–24 weeks: no effect on liver enzymes, blood pressure, glucose or lipids; heart rate lower by 3.92 beats/min; GRADE certainty very low — Jafari A, Mardani H, Mirzaei Fashtali Z, et al. Food Science & Nutrition, 2025;13(6):e70423. View on PubMed
• Pharmacovigilance — scoping review and VigiBase analysis of adaptogenic and immunomodulating natural products: reishi among the products most frequently associated with serious reports; causality unclear — Liang CJW, Woerdenbag HJ, Ekhart C, et al. Pharmaceuticals, 2025;18(8):1208. View on PubMed
• Children — 12-week randomized trial of yogurt enriched with reishi beta-glucans in 3- to 5-year-olds: safe and well tolerated; no rise in creatinine or liver aminotransferases — Henao SLD, Urrego SA, Cano AM, Higuita EA. International Journal of Medicinal Mushrooms, 2018;20(8):705-716. View on PubMed
• Critical review — clinical studies on chronic use, food and drink interactions, teratogenicity, mutagenicity and genotoxicity “are missing for Reishi” — Ahmad R, Riaz M, Khan A, et al. Phytotherapy Research, 2021;35(11):6030-6062. View on PubMed
• Product quality — 19 reishi supplements sold in the United States: only 5 (26.3%) matched their label ingredients — Wu DT, Deng Y, Chen LX, et al. Scientific Reports, 2017;7(1):7792. View on PubMed
• Allergy — skin-prick reactivity to Ganoderma spore extract in 30% of 33 allergic subjects and 44% of asthmatics — Rivera-Mariani FE, Nazario-Jiménez S, López-Malpica F, Bolaños-Rosero B. Medical Mycology, 2011;49(8):887-891. View on PubMed
• Reishi — 2,000 mg/day dry extract for 8 weeks in older women: modulates T-lymphocyte function (the basis of the immunosuppressant caution) — Iser-Bem PN, Lobato TB, Alecrim-Zeza AL, et al. British Journal of Nutrition, 2024;132(2):130-140. View on PubMed

Read next

• Side effects of medicinal mushrooms: what’s important to know
• Medicinal mushrooms and drug interactions
• Who shouldn’t take lion’s mane? Side effects, interactions and safety
• Reishi mushroom: the complete guide
• Reishi science — compounds and research
• Reishi for sleep — what was actually tested
• Reishi for stress and anxiety — every human trial
• Medicinal mushrooms in pregnancy and breastfeeding
• Medicinal mushrooms for children
• Medicinal mushroom dosage — drops, titration and what the trials used
• How long do medicinal mushrooms take to work?
• How to read a mushroom supplement test report (COA)
• Beta-glucan vs “polysaccharides” — the number that actually matters
• The full FAQ
• The research hub — reishi studies
• Functional mushrooms — the complete guide
• Full lab results

This page is educational and does not constitute medical advice. It describes what published trials and case reports recorded; it is not a prediction of what any individual will experience, and it is not a recommendation to start, stop or combine any supplement with any medication — those decisions belong with your physician. *These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.*