Reishi Mushroom Side Effects: What the Research Actually Shows (2026)

By Jimmy Daoutis, Founder of AdvancedMycoTech · Last updated: March 2026

Is Reishi Mushroom Safe?

For most healthy adults at standard doses (1.5–3g extract daily), reishi appears safe based on clinical trial data. In the largest randomized controlled trial to date, Klupp et al. (2016) gave 84 participants either reishi extract or placebo for 16 weeks. Liver and kidney function markers showed no significant changes between groups, and adverse events were mild and comparable to placebo.

A 2024 cross-sectional survey of cancer patients using reishi products found that the majority reported mild or no side effects, with gastrointestinal symptoms being the most common complaint.

But here’s the critical caveat: clinical trials use purified extracts from vetted suppliers, enroll relatively healthy participants, and run for 8–16 weeks. They don’t tell us what happens with cheap, poorly tested products, with compromised liver function, or with years of continuous use. And the case report literature tells a more complicated story than the trial data alone.

Documented Side Effects From Clinical Studies

Gastrointestinal Discomfort

The most commonly reported side effect across clinical research. In the Klupp 2016 RCT, participants taking reishi extract reported mild nausea, bloating, loose stools, and occasional diarrhea — but crucially, these rates were not significantly different from the placebo group. The Merck Manual lists nausea, insomnia, and chronic diarrhea among reported adverse effects.

Reishi’s triterpenes (ganoderic acids) are inherently bitter compounds and can irritate the stomach lining, particularly at higher doses or on an empty stomach. This is more common with concentrated extracts than with whole mushroom powder.

What this means practically: About 5–15% of people may experience mild stomach upset, especially during the first week or two of supplementation. Taking reishi with food and starting at a low dose (500mg) significantly reduces this risk. Most people who experience GI effects find they resolve within the first week as the body adjusts.

Dizziness and Headache

A small percentage of clinical trial participants have reported transient dizziness or headaches. These appear to be dose-dependent and more common with concentrated extracts versus whole mushroom preparations. In most cases, symptoms resolve within the first week of use or with dose reduction.

One possible mechanism: reishi’s documented effects on blood pressure. If you already have low blood pressure or take antihypertensive medication, even mild blood pressure reduction from reishi could trigger dizziness.

Insomnia (Paradoxical)

Despite reishi’s traditional reputation as a calming, sleep-promoting mushroom, some individuals report difficulty sleeping — especially with higher doses or evening administration. This appears to be an individual variation, possibly related to how specific triterpenes interact with different nervous systems. If you experience this, try taking reishi in the morning rather than at bedtime.

Allergic Reactions (Rare)

Allergic reactions to reishi are possible, particularly in individuals with existing mushroom sensitivities. Documented reactions include skin rashes, itching, and respiratory irritation. One case of hypereosinophilia with hepatic involvement has been reported after reishi use. If you have a known mushroom allergy, start with a very small dose and monitor carefully, or avoid reishi entirely.

The Liver Question: Rare but Serious

This is the most important section of this article. If you take away one thing, let it be this: reishi has been linked to liver injury in a small but real number of documented medical cases, and this risk is underreported by the supplement industry.

The NIH LiverTox database maintains a dedicated entry for reishi, cataloging cases of drug-induced liver injury (DILI) associated with Ganoderma lucidum products:

• Yuen et al. (2004): Documented fulminant hepatitis in an otherwise healthy patient after starting reishi powder. The patient recovered fully after discontinuation, and causality was assessed as probable.
• Wanmuang et al. (2007): Reported acute hepatitis in a patient taking reishi supplements in Thailand. Liver biopsy confirmed drug-induced injury consistent with the supplement use.
• PMC 2023 case report: A 47-year-old man developed severely elevated liver enzymes (ALT 990 U/L — normal is under 40) after taking reishi mushroom powder. This case was complicated by concurrent heavy alcohol use, making it difficult to isolate reishi as the sole cause.
• ACG 2025: Data presented at the American College of Gastroenterology noted that reishi-associated DILI cases now represent a growing proportion of supplement-associated liver injuries, paralleling the increase in consumer use.

Critical context: These are case reports, not controlled studies. In the millions of people who take reishi worldwide, documented liver injury cases number in the dozens. The absolute risk is very low. However, several factors amplify the risk significantly:

• Alcohol use: The PMC 2023 case involved concurrent heavy alcohol consumption. Alcohol and reishi both place metabolic demands on the liver, and combining them increases stress on that organ.
• Pre-existing liver disease: Anyone with compromised liver function, hepatitis, or fatty liver disease faces elevated risk from any hepatotoxic substance.
• Product quality: Contaminated or adulterated products may contain compounds not present in pure reishi extract. Products grown on contaminated substrates or poorly processed may carry elevated hepatotoxic risk.
• Duration and dose: Most case reports describe symptoms emerging after 1–3 months of continuous use. Higher doses and longer durations increase cumulative exposure.

Our recommendation: If you plan to take reishi daily for more than 8 weeks, consider requesting liver function markers (ALT, AST, bilirubin) as part of your regular blood work. This is especially important if you consume alcohol regularly, take medications metabolized by the liver, or have any history of liver disease. This is an easy, inexpensive precaution.

Drug Interactions

Reishi has documented pharmacological properties that can interact with specific medication categories. These aren’t theoretical concerns — they’re based on reishi’s established biochemical activity and are flagged by major medical institutions.

Anticoagulants and Antiplatelet Drugs

Risk level: High — consult your doctor before combining

Reishi mushroom has demonstrated antiplatelet and anticoagulant activity in laboratory studies. Both Memorial Sloan Kettering Cancer Center and Drugs.com explicitly warn that reishi may increase the risk of bleeding when combined with:

• Warfarin (Coumadin)
• Aspirin (high-dose therapeutic use)
• Clopidogrel (Plavix)
• Heparin and low-molecular-weight heparins
• NSAIDs at regular doses (ibuprofen, naproxen)

If you take any blood-thinning medication, do not start reishi without consulting your prescribing physician. This is a genuine safety concern, not a generic disclaimer.

Blood Pressure Medications

Risk level: Moderate — monitor blood pressure if combining

Several studies suggest reishi may lower blood pressure through vasodilatory effects. While this could be a benefit for people with hypertension, it can cause hypotension (dangerously low blood pressure) when stacked with antihypertensive medications like ACE inhibitors, beta-blockers, or calcium channel blockers. If combining, monitor your blood pressure regularly during the first few weeks.

Immunosuppressants

Risk level: Moderate — discuss with transplant/rheumatology team

Reishi is marketed as an “immune modulator,” and the clinical data supports this — it stimulates various immune pathways including natural killer cells and T-lymphocytes. This is the exact opposite of what immunosuppressive drugs are trying to achieve. If you’re on cyclosporine, tacrolimus, or similar drugs after organ transplant or for autoimmune conditions, adding reishi could theoretically undermine your therapy. The clinical evidence for this specific interaction is limited, but the pharmacological rationale is strong.

Diabetes Medications

Risk level: Low-Moderate — monitor blood sugar

Reishi has shown mild blood glucose-lowering effects in some studies. This could potentiate the effects of metformin, sulfonylureas, or insulin, increasing the risk of hypoglycemia. If you’re diabetic and want to try reishi, work with your doctor to monitor glucose levels during the first 2–4 weeks, and be aware of hypoglycemia symptoms (shakiness, sweating, confusion).

Who Should Avoid Reishi?

Based on the totality of evidence — clinical trials, case reports, pharmacological data, and institutional guidance — the following groups should either avoid reishi or use it only under direct medical supervision:

• People with liver disease or elevated liver enzymes — the hepatotoxicity risk, while rare, is not worth taking when your liver is already compromised
• People on anticoagulant or antiplatelet therapy — documented bleeding risk interaction flagged by MSKCC and Drugs.com
• Pregnant or breastfeeding women — no safety data exists for these populations. The Merck Manual lists this as a contraindication.
• People scheduled for surgery — discontinue reishi at least 2 weeks before any surgical procedure due to antiplatelet activity
• Organ transplant recipients or people on immunosuppressants — potential to counteract immunosuppressive therapy
• Heavy alcohol users — compounded liver stress based on case report evidence

Side Effect Comparison: Reishi vs. Other Mushroom Supplements

Reishi is not uniquely dangerous, but it does carry more documented interaction potential than the other popular mushroom supplements. Here’s how they compare:

• Reishi: Mild GI effects common. Rare liver injury (case reports). Antiplatelet activity interacts with blood thinners. Most drug interaction potential of any mushroom supplement.
• Lion’s Mane: Mild GI effects rare (~10%). No liver toxicity documented. No established drug interactions. Exceptionally clean safety profile.
• Cordyceps: Mild GI effects uncommon. No serious risks documented. Theoretical antiplatelet activity but weaker evidence than reishi.
• Turkey Tail: Mild GI effects and darkened stool. No serious risks documented. Theoretical immunosuppressant interaction.
• Chaga: Mild GI effects. Oxalate nephropathy risk at very high doses (unique concern). Antiplatelet activity similar to reishi.

Bottom line: reishi requires more caution than lion’s mane or turkey tail, roughly similar caution to chaga, and more monitoring than cordyceps. None of these mushrooms are dangerous for healthy adults at normal doses, but reishi is the one most likely to interact with medications.

How to Minimize Side Effects

1. Start low, titrate slowly: Begin with 500mg of extract daily and increase over 1–2 weeks to your target dose (typically 1–3g). This gives your body time to adjust and makes it easy to identify adverse reactions early.
2. Choose verified products: Use extracts from brands that provide third-party testing, COAs, and verified beta-glucan content. Contaminated products are a significant source of adverse events. Our best reishi supplements guide covers exactly what to look for.
3. Take with food: Reishi’s bitter triterpenes are less likely to cause GI upset when taken with a meal, especially one containing some fat (which may improve absorption as well).
4. Cycle your use: Consider 5 days on / 2 days off, or 4 weeks on / 1 week off. Continuous daily use for months without breaks is the pattern seen in most liver injury case reports.
5. Monitor with blood work: If taking reishi daily for more than 8 weeks, include liver function markers (ALT, AST, bilirubin) in your next routine blood panel. This is inexpensive and provides objective reassurance.
6. Separate from alcohol: On days you drink, skip your reishi dose. The liver handles both, and combining them increases cumulative metabolic stress.

What the Research Still Doesn’t Know

• Long-term safety: No clinical trial has tracked reishi supplementation beyond 16 weeks. What happens with years of daily use is simply unknown.
• Dose-response for hepatotoxicity: Case reports don’t consistently report dosages, making it impossible to establish a clear toxic threshold or safe upper limit.
• Product-specific risk variation: Different extraction methods, growing substrates, and Ganoderma species (G. lucidum vs. G. lingzhi vs. G. sinense) may carry different safety profiles. Most studies and case reports don’t differentiate.
• Genetic susceptibility: Some individuals may be genetically predisposed to reishi-related liver injury. This is an established phenomenon for other DILI-causing compounds (certain antibiotics, for example) but hasn’t been investigated for reishi.
• Clinical significance of antiplatelet activity: We know reishi inhibits platelet aggregation in vitro, but the clinical magnitude at typical supplement doses (versus the laboratory concentrations used in studies) remains unclear.

Evidence Strength Assessment

• GI discomfort (nausea, diarrhea): Well-documented — RCTs + cancer patient surveys (Klupp 2016, cross-sectional 2024)
• Liver injury (hepatotoxicity): Rare but serious — multiple case reports, NIH LiverTox entry, ACG 2025 data
• Increased bleeding risk: Pharmacologically established — in vitro antiplatelet activity (PMC 6950045), institutional warnings (MSKCC, Drugs.com)
• Dry mouth/throat/nasal passages: Anecdotal — consumer self-reports, not documented in clinical trials
• Dizziness/headache: Uncommon — reported in clinical settings, likely dose-dependent
• Allergic reactions: Rare — case reports of hypersensitivity, hypereosinophilia

FAQ

Can reishi damage your liver?

Rare but documented. Multiple case reports have linked reishi use to liver injury, including significantly elevated liver enzymes and, in isolated cases, acute hepatitis requiring hospitalization. The NIH maintains a specific LiverTox entry for reishi. However, the largest clinical trial (Klupp 2016, 16 weeks) showed no liver function changes versus placebo. The absolute risk appears very low for healthy adults using quality products at standard doses, but it increases with concurrent alcohol use, pre-existing liver conditions, and prolonged continuous use.

Is it safe to take reishi every day?

For most healthy adults, daily reishi at 1–3g of extract appears safe based on clinical data up to 16 weeks. No long-term safety data exists beyond that timeframe. We recommend cycling (4 weeks on / 1 week off) rather than continuous daily use, and periodic liver function monitoring if supplementing for extended periods. This is more conservative than what most supplement brands suggest, but it’s what the evidence actually supports.

Does reishi interact with medications?

Yes, and more so than other mushroom supplements. Reishi has documented antiplatelet/anticoagulant activity and should not be combined with blood-thinning medications (warfarin, aspirin, clopidogrel, heparin) without physician approval. It may also interact with blood pressure medications (additive hypotensive effect), diabetes drugs (additive blood sugar lowering), and immunosuppressants (opposing pharmacological action). Always disclose reishi use to your prescribing doctor.

Can reishi cause allergic reactions?

Yes, though this is rare. Reported reactions include skin rashes, itching, respiratory irritation, and at least one case of hypereosinophilia. People with known mushroom allergies are at higher risk. If you suspect a mushroom sensitivity, start with a very small dose (250mg) and wait 24 hours before increasing.

Should I stop taking reishi before surgery?

Yes. Due to reishi’s antiplatelet properties, most integrative medicine guidelines and surgical protocols recommend discontinuing reishi supplements at least 2 weeks before any scheduled surgery. This reduces the risk of excessive bleeding during the procedure. Always inform your surgical team about all supplements you take — they need a complete picture to keep you safe.

Related Reading

• Best Mushroom Supplements for Sleep (2026)
• Reishi Mushroom Benefits: What the Science Actually Shows
• Reishi Mushroom Dosage: How Much to Take
• Best Reishi Mushroom Supplements (2026)
• Lion’s Mane Side Effects: What the Research Shows
• Chaga Dosage Guide (Includes Oxalate Safety)
• The Best Mushroom Supplements of 2026

Medical disclaimer: This article is for informational purposes only and does not constitute medical advice. Consult your healthcare provider before starting any supplement. AdvancedMycoTech may earn a commission from affiliate links at no extra cost to you.