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Ingredient guide

Reishi side effects: what trials and case reports show

Written by the Full Measure editorial team, which sells supplements. Approved for publication by the Full Measure owners. Updated .

Drafted with AI assistance from the sources listed below. How we write these

Quick answer

Short trials of reishi in healthy adults, lasting 10 days to 12 weeks, reported few side effects. The main concern is rare liver injury: LiverTox rates reishi a possible rare cause, with trouble usually starting 1 to 2 months in and most people recovering within 1 to 3 months of stopping.1,2,3

Key facts

  • Clotting and platelet tests did not change in 40 healthy volunteers taking 1.5 g a day for four weeks.4
  • A 12-week trial of a purified extract found no change in kidney or liver blood tests.2
  • Four weeks at 1.44 g a day showed no sign of liver, kidney or DNA harm in 18 healthy adults.5
  • LiverTox says many reported liver cases were poorly documented, with other causes not always ruled out.3

What trials report

Small, short trials have reported few or no side effects, and there is little information on common side effects in people.1,3

In a 10-day trial, 16 healthy volunteers took 2 g of extract twice a day or a placebo while researchers checked heart tracings, blood counts, blood chemistry and urine. They found no adverse effects compared with placebo.1

In the 12-week trial of a purified beta-glucan, a safety board reviewed the data at six weeks, found no adverse events reported, and saw no need for further checks. Kidney and liver blood tests did not shift in either group.2

In trials of 1.4 to 3 g a day for 12 to 16 weeks in adults with type 2 diabetes, side effects were reported somewhat more often with reishi than with placebo, a difference that may be due to chance. None was serious.6

Rare liver injury

Rare cases of liver injury have been reported, usually 1 to 2 months after starting reishi, with tiredness, nausea, stomach pain, poor appetite, dark urine or yellowing of the skin and eyes. Most people recovered within 1 to 3 months of stopping, but one woman died.3

In two of the reported liver cases, the trouble began after the person switched to a powdered reishi product.3

LiverTox rates reishi a possible rare cause of liver injury (category D) and notes that many reported cases were poorly documented, with other causes not always ruled out.3

Signs to act on after starting reishi: dark urine, yellowing of the skin or the whites of the eyes, nausea, belly pain, loss of appetite or unusual tiredness. Stop taking it and contact a doctor. In the published cases, recovery was usually quick once the product was stopped, and no case became long-lasting.3

LiverTox also notes that liver tests stayed normal in the small placebo-controlled trials, and that large registries of supplement-related liver injury in the United States, Spain and Latin America did not list reishi. Given how widely it is used, it concludes that serious liver injury must be extremely rare.3

Bleeding and blood thinners

In 40 healthy volunteers, 1.5 g of reishi a day for 4 weeks did not change blood clotting or platelet tests, despite earlier laboratory reports that it slows platelets.4

That trial was small, short and in healthy people, so it cannot rule out an effect in someone already taking a blood thinner. The warfarin label notes that few well-controlled studies have tested herbal products with warfarin, and asks for more frequent INR checks when one is started or stopped.4,7

The official sources we rely on do not name reishi as interacting with any particular medicine. Bring the product to your pharmacist so they can check it against everything you take.

Who should ask a doctor first

  • People with liver disease, or anyone who has had a liver reaction to a supplement
  • Anyone taking a blood thinner or an antiplatelet medicine, or with surgery coming up
  • People taking medicines for blood sugar, blood pressure or immune suppression
  • People under cancer care, since reishi has been used alongside chemotherapy3
  • Anyone pregnant or breastfeeding

Product quality

When 19 reishi supplements bought in the United States were analyzed, the measured triterpenes and polysaccharides matched the label in only 5.8

That matters for safety as well as value. LiverTox notes that in some reported liver cases, other herbal products or contaminants in the product were not ruled out as the cause.3

Questions people ask

Is reishi safe to take daily?

For a few weeks to a few months, trials in healthy adults found few problems. Daily use beyond 24 weeks has not been studied, and the rare liver reaction can appear after a month or two, so watch for dark urine or yellowing skin.3,9

Can reishi upset your stomach?

Stomach complaints did not stand out in the healthy-adult trials. But nausea, stomach pain and loss of appetite can also be early signs of the rare liver reaction, so if they appear after starting reishi, stop it and check with a doctor.1,3

Do reishi extracts and powders differ in side effects?

We found no study comparing them. In two of the reported liver cases the trouble began after a switch to a powdered product, but there are too few cases to say any form is riskier.3

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Sources

  1. Wicks SM, Tong R, Wang CZ, O'Connor M, Karrison T, Li S, Moss J, Yuan CS. Safety and tolerability of Ganoderma lucidum in healthy subjects: a double-blind randomized placebo-controlled trial. Am J Chin Med. 2007;35(3):407-414. Opened 2026-10-07.
  2. Chen SN, Nan FH, Liu MW, Yang MF, Chang YC, Chen S. Evaluation of Immune Modulation by β-1,3; 1,6 D-Glucan Derived from Ganoderma lucidum in Healthy Adult Volunteers, A Randomized Controlled Trial. Foods. 2023;12(3):659. Opened 2026-10-07.
  3. LiverTox: Clinical and Research Information on Drug-Induced Liver Injury. Lingzhi, Reishi. Bethesda (MD): National Institute of Diabetes and Digestive and Kidney Diseases. Last update October 5, 2024. Opened 2026-10-07.
  4. Kwok Y, Ng KFJ, Li CCF, Lam CCK, Man RYK. A prospective, randomized, double-blind, placebo-controlled study of the platelet and global hemostatic effects of Ganoderma lucidum (Ling-Zhi) in healthy volunteers. Anesth Analg. 2005;101(2):423-426. Opened 2026-10-07.
  5. Wachtel-Galor S, Tomlinson B, Benzie IF. Ganoderma lucidum ("Lingzhi"), a Chinese medicinal mushroom: biomarker responses in a controlled human supplementation study. Br J Nutr. 2004;91(2):263-269. Opened 2026-10-07.
  6. Klupp NL, Chang D, Hawke F, Kiat H, Cao H, Grant SJ, Bensoussan A. Ganoderma lucidum mushroom for the treatment of cardiovascular risk factors. Cochrane Database Syst Rev. 2015;(2):CD007259. Opened 2026-10-07.
  7. Warfarin sodium tablets: prescribing information (A-S Medication Solutions). DailyMed, U.S. National Library of Medicine. Published September 23, 2026. Opened 2026-10-07.
  8. Wu DT, Deng Y, Chen LX, Zhao J, Bzhelyansky A, Li SP. Evaluation on quality consistency of Ganoderma lucidum dietary supplements collected in the United States. Sci Rep. 2017;7(1):7792. Opened 2026-10-07.
  9. Jafari A, Mardani H, Mirzaei Fashtali Z, Arghavan B. The Nutritional Significance of Ganoderma lucidum on Human Health: A GRADE-Assessed Systematic Review and Meta-Analysis of Clinical Trials. Food Sci Nutr. 2025;13(6):e70423. Opened 2026-10-07.

This page is information, not medical advice. Talk to your doctor or pharmacist about your own situation.