Lion's Mane Side Effects: What the Evidence Reports

Lion's mane has gone from an obscure culinary mushroom to a fixture of the UK supplement aisle in about five years, and the questions have followed it. What actually happens if you take it every day? Is there anything in the literature worth knowing before you start?

The honest answer is that the reported side effects are few and mild, and that the reason there are so few is partly that the trials have been small and short. Both halves of that sentence matter. Here is what has been documented.

TL;DR

• Digestive upset is the commonest report — abdominal discomfort, nausea or loose stools, in under one in ten trial participants on prolonged dosing, according to LiverTox^[1].
• Skin rash has been recorded in a long trial: of 49 people randomised to a 49-week study, four withdrew citing abdominal discomfort, nausea and skin rash — three of them from the mushroom arm, one from placebo^[2].
• No liver signal. LiverTox reports no case of clinically apparent liver injury attributed to lion's mane and scores it E — unlikely cause^[1].
• One theoretical bleeding mechanism. A laboratory study found hericenone B inhibited collagen-induced platelet aggregation in human platelets^[3]. That is a test-tube result, not a documented human bleed — but it is why anticoagulant users should ask a pharmacist.
• Allergy is the clearest hard stop. Lion's mane is a mushroom. If you react to mushrooms, do not take it.
• The evidence base is thin, not clean. The trials typically enrol 20–40 people for four to sixteen weeks. Absence of reported harm at that scale is weak reassurance, not proof of safety.

What lion's mane is, in one paragraph

Hericium erinaceus is an edible mushroom with a shaggy white fruiting body — yamabushitake in Japan, hóutóugū in China, lion's mane or bearded tooth in English. It has been eaten as food in East Asia for centuries, which is one reason often given for its straightforward arrival in the Western supplement aisle. Supplements use either the fruiting body or the mycelium, and the two are not interchangeable in composition.

That distinction matters more than it sounds, and it matters twice. It decides what is actually in a jar, and it decides whether two trials are even measuring the same substance — because the published studies use both. A mycelial preparation is grown on grain and harvested with the substrate; a fruiting-body powder is the mushroom itself. Keep the difference in view for the rest of this page.

The side effects that have actually been reported

There is no large post-marketing surveillance dataset for lion's mane, so the reported-effects picture is assembled from clinical trials and a small number of case reports. Below is what those sources record.

Digestive effects

This is the category that turns up most often, and it is the one you would predict for a mushroom taken as a powder or an extract. LiverTox — the National Institute of Diabetes and Digestive and Kidney Diseases database of liver injury from drugs and supplements — summarises the pattern as mild abdominal discomfort, nausea or diarrhoea in fewer than one in ten treated subjects in trials of prolonged therapy^[1]. Note what that denominator is: people enrolled in a study and monitored, not the general population buying a jar.

In practical terms it is the sort of effect that usually settles when a supplement is taken with food rather than on an empty stomach, though nobody has run a trial to confirm that. It is also the reason the format matters — a gummy taken with a meal lands differently from a capsule swallowed first thing on an empty stomach.

Skin reactions

The longest published human trial of lion's mane, as of August 2026, ran for 49 weeks. Two things about it need stating before its numbers are quoted. It enrolled people with mild Alzheimer's disease, not healthy volunteers; and it was run with the manufacturer of the erinacine-A ingredient, Grape King Bio, which supplied the study material and paid several of the authors^[2]. Neither fact invalidates the safety reporting, but both belong next to it.

Forty-nine people were randomised and 41 completed. Four dropped out because of side effects, and the authors record the reasons plainly: "Except for four subjects who dropped out of the study due to abdominal discomfort, nausea, and skin rash, no other adverse events were reported"^[2]. Three of those four were in the mushroom arm and one was on placebo — a distinction the paper makes and most summaries of it do not. That is a small number, but it is the only long-duration adverse-event record that exists, and skin rash appears in it.

Allergy

Lion's mane is a fungus, and fungi cause allergic reactions. LiverTox notes that at least one example of an acute hypersensitivity reaction to oral lion's mane has been described^[1]. Anyone with a known mushroom or mould allergy should read that as a contraindication rather than a caution. Symptoms of an allergic reaction — a spreading rash, swelling of the face or throat, wheezing, difficulty breathing — need urgent medical attention, and the NHS guidance on allergies sets out when to call 999^[5].

What the liver data shows

This is worth separating out, because "is it hard on the liver?" is one of the most-asked questions about any daily supplement, and here there is a specific answer rather than a shrug.

LiverTox assigns lion's mane a hepatotoxicity likelihood score of E — "unlikely cause of clinically apparent liver injury", the lowest category on its A-to-E scale. Its entry states that there have been no case reports of clinically apparent liver injury attributed to lion's mane, that it "has not been linked to serum enzyme elevations during therapy", and that it "is not mentioned or listed in large case series or systematic reviews" of supplement-induced liver injury^[1].

Read that as an absence of a signal rather than a guarantee. A supplement can only accumulate case reports in proportion to how many people take it and how closely they are watched, and lion's mane is newer to mass use in the UK than, say, green tea extract. But on the evidence available, the liver is not where the concern sits.

The bleeding question

A 2010 laboratory study found that hericenone B, one of the compounds in lion's mane, inhibited collagen-induced aggregation of human platelets in vitro^[3]. Platelet aggregation is the first step in forming a clot, so a compound that slows it is, in principle, something to think about alongside warfarin, a DOAC, clopidogrel or regular aspirin.

What does not exist is any published human case of bleeding attributed to lion's mane, or any trial that measured clotting times in people taking it. So the honest characterisation is: a plausible mechanism demonstrated in a test tube, with no clinical evidence either way. If you take an anticoagulant or antiplatelet medicine, or you have surgery scheduled, that is a conversation to have with your GP or pharmacist before starting — the same advice the NHS gives for supplements generally^[6].

How much has actually been studied

Trial doses vary by almost tenfold, which is worth knowing when a jar's serving size looks either tiny or enormous next to what you have read elsewhere.

The spread is the point. Li and colleagues used three 350 mg capsules a day of an erinacine-A-enriched mycelial preparation for 49 weeks^[2]. Mori and colleagues gave 3 g a day of dried fruiting-body powder for 16 weeks to 30 older adults, with liver and kidney markers staying within range throughout^[4]. Grozier and colleagues went to 10 g a day for four weeks, delivered in muffins^[7].

A concentrated extract and a raw powder are not the same thing at the same weight. That is why comparing two labels by milligrams alone is misleading unless both state the extract ratio.

Who should be cautious

• Anyone with a mushroom or mould allergy. The straightforward one — do not take it.
• Anyone taking an anticoagulant or antiplatelet medicine, or with surgery booked, because of the in-vitro platelet finding^[3]. Ask a pharmacist first.
• Pregnancy and breastfeeding. No trial has assessed lion's mane in either group, so there is no safety data to rely on. The NHS advises particular care with supplements in pregnancy^[6].
• Children. Same reason — the trials enrol adults.
• Anyone on prescribed medication for a long-term condition. Not because a specific interaction is documented, but because none has been ruled out either.

What a UK label may and may not say about it

Lion's mane is a botanical, and botanical health claims sit on the "on hold" list in the Great Britain nutrition and health claims register^[8] — assessments were never completed, so no claim about lion's mane has been authorised. In practical terms, a GB supplement label may tell you what is in the jar and how much, and may not make any claim about what it does in the body^[9]. Any product that does is breaking the rules, and the confidence of the wording is not evidence of anything.

That is why Vitgem's ashwagandha gummies, which include lion's mane alongside KSM-66 ashwagandha and ginkgo, carry their function claims on vitamins B6 and B12 — the ingredients that hold authorised entries in the register.

If you want the fuller picture of what the research on this mushroom does and does not cover, our guide to lion's mane benefits and the state of the evidence goes through the trials one by one, and how long ashwagandha takes to work covers the same question for the other botanical in that formula.

Reporting a suspected reaction

If you think a supplement has caused you a side effect, it is worth reporting rather than only stopping. The route depends on what the product legally is, and this catches people out. The MHRA's Yellow Card scheme takes reports about medicines, vaccines and registered herbal medicines — but a lion's mane supplement is sold as a food, so it falls outside it. Reactions to a food supplement go to the food-safety team at your local authority, which is the enforcement route the FSA sets out^[10].

Tell your pharmacist or GP as well, particularly if you take prescribed medication. For a botanical with an evidence base this thin, individual reports are most of how the picture improves.

Frequently asked questions

What are the side effects of lion's mane?

The reported effects in published human trials are mild abdominal discomfort, nausea and diarrhoea in fewer than one in ten treated subjects, plus skin rash recorded among the withdrawal reasons in one long trial. At least one case of an acute hypersensitivity reaction has been described.

Is lion's mane bad for your liver?

There is no evidence that it is. The NIH LiverTox database records no case reports of clinically apparent liver injury attributed to lion's mane and gives it a likelihood score of E, the lowest category.

Can you take lion's mane every day?

The trials have used daily dosing for four weeks to 49 weeks without a serious safety signal. That said, they are small studies, so daily use over years has not been formally assessed. Follow the serving size on the pack.

Does lion's mane interact with blood thinners?

No human interaction has been documented, but a laboratory study found one of its compounds slowed platelet aggregation. If you take warfarin, a DOAC, clopidogrel or regular aspirin, check with your pharmacist before starting.

Can you take lion's mane while pregnant?

There is no safety data in pregnancy or breastfeeding, because no trial has enrolled either group. Speak to your midwife or GP rather than relying on an absence of reported harm.

Does lion's mane cause headaches?

Headache is sometimes listed anecdotally, but no clinical trial has recorded it as a significant adverse event at the doses studied. It is not in the LiverTox summary of reported effects.

How long do lion's mane side effects last?

The digestive effects described in the literature are mild and transient. If any effect persists after you stop taking it, or if you develop a rash or swelling, stop and speak to a pharmacist or GP.

This article is general information about nutrition and food supplements, not medical advice. Food supplements are not a substitute for a varied diet and a healthy lifestyle. If you are taking prescribed medication, are pregnant or breastfeeding, or have a medical condition, speak to your GP or pharmacist before starting a supplement.