Does lion's mane cause diarrhea?

What NIH's liver injury database says

LiverTox, the NIH database of liver injury from medicines and supplements, covers lion's mane because the question is whether it harms the liver, and rates it an unlikely cause of clinically apparent liver injury. It also summarizes tolerability. It says the few short trials in humans reported few adverse events, and that in trials of prolonged use mild gastrointestinal complaints of abdominal discomfort, nausea or diarrhea were reported, usually in fewer than 10% of treated people and generally without needing the product to be stopped.¹

The entry gives no figure for diarrhea alone. It notes that lion's mane has not been through prospective trials of its safety.¹

What the longer trials reported

Stomach discomfort, nausea or diarrhea, reported by under 10% of people in longer trials.^1,2

Skin rash. In a 49-week trial, 3 people taking lion's mane stopped because of stomach discomfort, nausea or a rash, against 1 on placebo who stopped because of nausea.²

In a trial of 30 adults aged 50 to 80 who took about 3 g a day of fruiting body powder for 16 weeks, the abstract reports no adverse effect on laboratory tests. LiverTox's summary of the same trial says the side effects were limited to mild abdominal discomfort and diarrhea.^1,3

What the shorter trials reported

A single 1 g dose in 40 adults was followed by no adverse events. The abstracts we read for trials of 1.8 g a day for 28 days, a single 3 g dose and 10 g a day for 4 weeks do not mention diarrhea.^5,6,7,8

An abstract that is silent about diarrhea has not shown that none occurred, which is why the sources cannot give a rate.⁴

What a 2025 systematic review says

A 2025 systematic review of lion's mane as a supplement, which drew on randomized trials and laboratory work, lists stomach discomfort, headache and allergic reactions as possible side effects, and says side effects are commonly unreported. Its abstract gives no rate for diarrhea.⁴

Why the answer is uncertain

• The trials are small, from 18 to 49 people each, and most are short.^2,7
• Products differ. The trials used about 3 g a day of fruiting body powder, three 350 mg capsules a day of a cultured mycelium, or 10 g a day baked into muffins.^2,3,8
• Side effects are often not reported, so a silence in a paper is not a negative result.⁴

When diarrhea needs a provider

MedlinePlus says diarrhea is loose stools three or more times in a day and usually passes in a day or two. For adults it lists the signs for contacting a provider as signs of dehydration, diarrhea lasting more than 2 days, severe pain in the abdomen or rectum, a fever of 102 degrees or higher, stools with blood or pus, and black, tarry stools.⁹

Infections, medicines and food intolerances are among the common causes of diarrhea, so a person who starts lion's mane and then has diarrhea cannot assume the mushroom caused it.⁹

Who should ask a doctor or pharmacist first

• Anyone who has had an allergic reaction to lion's mane or another mushroom. LiverTox describes at least one acute hypersensitivity reaction to oral lion's mane, and a 63-year-old man in Japan had a severe lung reaction linked to an extract.^1,10
• Anyone who takes prescription medicines every day. No official source we read documents an interaction between lion's mane and a medicine, which is not the same as showing that none exists.
• Anyone with diarrhea that lasts or comes with the signs MedlinePlus lists.⁹

Questions people ask

Sources

1. LiverTox: Clinical and Research Information on Drug-Induced Liver Injury. Lion's Mane. Bethesda (MD): National Institute of Diabetes and Digestive and Kidney Diseases. Last update January 5, 2024. Opened 2026-10-01.
2. Li IC, Chang HH, Lin CH, et al. Prevention of early Alzheimer's disease by erinacine A-enriched Hericium erinaceus mycelia pilot double-blind placebo-controlled study. Front Aging Neurosci. 2020;12:155. Opened 2026-10-07.
3. Mori K, Inatomi S, Ouchi K, Azumi Y, Tuchida T. Improving effects of the mushroom Yamabushitake (Hericium erinaceus) on mild cognitive impairment: a double-blind placebo-controlled clinical trial. Phytother Res. 2009;23(3):367-372. Opened 2026-10-07.
4. Menon A, Jalal A, Arshad Z, Nawaz FA, Kashyap R. Benefits, side effects, and uses of Hericium erinaceus as a supplement: a systematic review. Front Nutr. 2025;12:1641246. Opened 2026-10-07.
5. La Monica MB, Raub B, Ziegenfuss EJ, et al. Acute effects of naturally occurring guayusa tea and Nordic lion's mane extracts on cognitive performance. Nutrients. 2023;15(24):5018. Opened 2026-10-07.
6. Docherty S, Doughty FL, Smith EF. The acute and chronic effects of lion's mane mushroom supplementation on cognitive function, stress and mood in young adults: a double-blind, parallel groups, pilot study. Nutrients. 2023;15(22):4842. Opened 2026-10-07.
7. Surendran G, Saye J, Binti Mohd Jalil S, et al. Acute effects of a standardised extract of Hericium erinaceus (Lion's Mane mushroom) on cognition and mood in healthy younger adults: a double-blind randomised placebo-controlled study. Front Nutr. 2025;12:1405796. Opened 2026-10-07.
8. Grozier CD, Alves VA, Killen LG, Simpson JD, O'Neal EK, Waldman HS. Four weeks of Hericium erinaceus supplementation does not impact markers of metabolic flexibility or cognition. Int J Exerc Sci. 2022;15(2):1366-1380. Opened 2026-10-07.
9. MedlinePlus Health Topics. Diarrhea. National Library of Medicine; content from the National Institute of Diabetes and Digestive and Kidney Diseases. Read October 11, 2026. Opened 2026-10-11.
10. Nakatsugawa M, Takahashi H, Takezawa C, et al. Hericium erinaceum (yamabushitake) extract-induced acute respiratory distress syndrome monitored by serum surfactant proteins. Intern Med. 2003;42(12):1219-1222. Opened 2026-10-07.