Lion's Mane Side Effects: Dangers of the Mushroom and Who Should Avoid It

The verdict in brief

Lion's mane dangers: a reassuring profile, not a blank cheque.

Lion's mane is an edible mushroom: Hericium erinaceus. In Japan and China it has been cooked for centuries, and it is sold fresh in some European markets. This culinary history is a useful first marker. It does not tell the whole story, because a supplement sometimes concentrates far more mushroom than a plateful, but it sets the scene: we are not talking about a plant with known toxicity.

Clinical trials in humans, at doses of 1 to 3 g a day of powder or extract, for a few weeks to almost a year, have not shown any toxicity. Literature reviews, such as Mendel Friedman's in 2015, reach the same conclusion. That does not mean “zero risk”. Here is what to bear in mind before taking it.

• The side effects reported are rare, and mostly digestive: abdominal discomfort, nausea, looser stools.
• Allergy exists, as with any mushroom. It remains exceptional, but it means you must stop.
• Interactions with anticoagulants and diabetes medicines are theoretical, based on laboratory studies. They justify medical advice if you are on treatment.
• Pregnancy, breastfeeding and children: no data, so no lion's mane supplements.
• Quality matters as much as dose: origin, part used, contaminant testing.

For the benefits studied, the dosage and the history of the mushroom, our reference article on lion's mane benefits and dosage covers everything. Here, we focus on the question of safety.

Side effects

Lion's mane side effects: rare, and mostly digestive.

In published trials, the vast majority of participants reported no troublesome effects. When effects do appear, they are almost always the same ones, and they go away when you stop. Here is how to recognise them and what to do.

Summary of effects described in clinical trials and published cases. Frequencies are qualitative: the trials are small and cannot put a precise figure on rare effects.

Watch out for a common trap: many lion's mane supplements contain other ingredients. A blend with caffeine, ginkgo or fibre can cause an effect that you wrongly attribute to the mushroom. Always read the full list.

The mushroom's own fibres, including beta-glucans, can also cause a little wind at first in sensitive guts. If your stomach reacts, the rule is the same as for any fibre: start low and go up slowly.

Allergy and asthma

Mushroom allergy, asthma: the real cases to know about.

This is the best-documented risk, even though it remains exceptional. Like any mushroom, lion's mane contains proteins that can trigger a reaction in a sensitised person. Two published cases are regularly cited in reviews of its safety.

Two published cases for a mushroom eaten for centuries by millions of people is very few. But it is the reason why it is always recommended to introduce a new supplement on its own, at a reduced dose, for a few days, so you know what to blame for any reaction.

Interactions

Anticoagulants, diabetes medicines: interactions that are mostly theoretical.

No serious interaction with a medicine has been demonstrated in humans. But laboratory and animal studies have observed effects that, in theory, could add to those of certain treatments. In the absence of human data, the right approach is simple: talk to your doctor or pharmacist.

“Theoretical” means: observed in vitro or in animals, never demonstrated in treated patients. It is no reason to panic, but it is a reason to tell your doctor.

Autoimmune diseases follow the same logic. Medicinal mushrooms act on certain cells of the immune system in laboratory studies. If you are being treated for a disease of this kind, do not start anything without discussing it first. For an overview, our article on the risks of mushrooms and adaptogenic plants reviews them species by species.

Pregnancy and children

Pregnancy, breastfeeding, children: no data, so avoid it.

No trial has assessed lion's mane supplements in pregnant women, breastfeeding women or children. That is not a danger signal: it is an absence of information. But in health, an absence of data calls for caution, especially when simple alternatives exist.

• Pregnant: no lion's mane supplements, whatever the form. The mushroom cooked occasionally, and cooked well, is not concerned in the same way.
• Breastfeeding: the same rule, as we do not know whether its compounds pass into breast milk.
• Children and teenagers: no supplements, for lack of data on growth and development.
• Planning a pregnancy: discuss all your supplements with your doctor or midwife.

For drinks that combine lion's mane with caffeine, such as mushroom coffees, there is another benchmark: EFSA recommends that pregnant women do not exceed 200 mg of caffeine a day, from all sources combined.

Quality and contaminants

The real risk often lies in the product, not the mushroom.

Mushrooms have one particular feature: they absorb what is in their substrate, including heavy metals such as lead, cadmium or mercury. A mushroom grown on a contaminated substrate can therefore concentrate them. That is why the European Union sets maximum levels of heavy metals for food supplements, and why lab tests matter.

At Mush n Go, the Lion's Mane in Brainstoorm comes from the fruiting body, at 1,000 mg per cup, and our recipes are blended in Toulouse. The lab results for our mushrooms can be viewed on our lab tests page, something some customers point out.

Trustpilot review published about Mush n Go, quoted as written.

Dose and when to stop

The right dose, and the signs that mean you should stop.

Human trials used 1 to 3 g a day of fruiting body powder, or lower doses of concentrated extracts. There is no official dose. The safest rule is to stick to the dose stated on the label of the product you buy, without exceeding it or combining several lion's mane products. For detailed guidance, see our lion's mane page.

Stop immediately in case of itching, skin rash, swelling, breathing difficulty, unusual bleeding or feeling faint. For mild digestive problems, reducing the dose and taking it with a meal is usually enough.

If you are mainly looking for support during periods of intense work, remember that sleep, physical activity and breaks carry far more weight than a supplement. Our guide to natural nootropics puts each option in its place.

Who should avoid

Situations where you should avoid it, or ask first.

For the vast majority of healthy adults, lion's mane taken at a usual dose poses no known problem. Here, however, are the cases where it is better to avoid it, or to ask a health professional.

A food supplement does not replace treatment or medical advice. If you have memory or concentration problems that worry you, talk to your doctor first: they often have causes that are simple to identify. And if you are comparing several species, our list of medicinal mushrooms presents the twelve most studied.

Sources

1. Mori K., Inatomi S., Ouchi K., Azumi Y., Tuchida T. (2009). Improving effects of the mushroom Yamabushitake (Hericium erinaceus) on mild cognitive impairment: a double-blind placebo-controlled clinical trial. Phytotherapy Research, 23(3), 367-372.
2. Li I. C. et al. (2020). Prevention of early Alzheimer's disease by erinacine A-enriched Hericium erinaceus mycelia pilot double-blind placebo-controlled study. Frontiers in Aging Neuroscience, 12, 155.
3. Docherty S. et al. (2023). 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, 15(22), 4842.
4. Friedman M. (2015). Chemistry, nutrition, and health-promoting properties of Hericium erinaceus (lion's mane) mushroom fruiting bodies and mycelia and their bioactive compounds. Journal of Agricultural and Food Chemistry, 63(32), 7108-7123.
5. Maes M. F., van Baar H. M., van Ginkel C. J. (1999). Occupational allergic contact dermatitis from the mushroom White Pom Pom (Hericium erinaceum). Contact Dermatitis, 40(5), 289-290.
6. Nakatsugawa M. et al. (2003). Hericium erinaceum (yamabushitake) mushroom-induced acute respiratory distress syndrome. Nihon Kokyuki Gakkai Zasshi (Journal of the Japanese Respiratory Society).
7. Mori K. et al. (2010). Inhibitory effect of hericenone B from Hericium erinaceus on collagen-induced platelet aggregation. Phytomedicine, 17(14).
8. Regulation (EU) 2023/915 on maximum levels for certain contaminants in food.
9. EFSA NDA Panel (2015). Scientific opinion on the safety of caffeine. EFSA Journal, 13(5):4102.

Keep reading

Further reading.

Safety is only part of the story. Explore our other guides on lion's mane, or our mushroom coffee Brainstoorm.