Lion's Mane Side Effects: What the Research Shows, Who Should Avoid It and How Much to Take

Lion's mane (Hericium erinaceus) has gone from a niche mushroom to one of the UK's most popular supplements. If you're thinking about taking it, or you've just started, it's sensible to ask what the downsides are.

This guide sets out what published research reports, who should check with a GP or pharmacist first, and how much people typically take, without the hype in either direction.

The quick answer

In the human studies published so far, lion's mane has generally been well tolerated. The side effects reported are uncommon and usually mild: stomach discomfort, loose stools, headache and, rarely, allergic reactions. The main groups who should check with a health professional first are people with mushroom allergies, people taking blood-thinning or diabetes medication, and anyone pregnant or breastfeeding.

What the research says about safety

The most complete recent summary is a 2025 systematic review in Frontiers in Nutrition, which pulled together clinical trials, pilot studies and case reports on lion's mane as a supplement. Its conclusion on safety: side effects are not commonly reported, and the potential ones are stomach discomfort, headache and allergic reactions. (Menon et al., 2025)

A separate 2025 toxicology study tested lion's mane powder in rats at doses far above normal human use, over 90 days, and found no treatment-related adverse effects. (Frontiers in Toxicology, 2025)

Two honest caveats:

Most human trials have been small and have lasted weeks or months, not years. Rare side effects could be missed.
Few studies have tested lion's mane alongside medicines, so interaction advice is mostly precautionary (see below).

Possible side effects

Stomach discomfort or loose stools

The most commonly mentioned side effect. It tends to be mild and often settles after the first week or so. Taking lion's mane with food, or starting with half a serving, can help.

Headache

Listed in the 2025 review as an occasional report. If it persists, stop and speak to a pharmacist.

Allergic reactions

Rare, but documented, including skin rashes and, in isolated case reports, more serious reactions. If you're allergic to mushrooms or moulds, don't take lion's mane without advice. Stop immediately and get medical help if you notice swelling, wheezing or difficulty breathing.

Feeling restless, anxious or having vivid dreams

You'll find these in online forums, but they haven't shown up consistently in clinical trials. Some people find taking lion's mane in the morning rather than the evening suits them better. If you feel unwell, stop taking it.

Who should check with a GP or pharmacist first

People with mushroom allergies. See above.
People taking blood thinners or antiplatelet medicines (such as warfarin, apixaban, clopidogrel or daily aspirin). Some lab research suggests mushroom compounds may affect platelets. This hasn't been confirmed in people, but it's worth a conversation, especially before surgery.
People taking diabetes medication. Animal studies suggest lion's mane may affect blood sugar, which could add to the effect of medicines that lower it.
People taking immunosuppressants. Mushroom beta-glucans interact with the immune system, and the effect alongside these medicines hasn't been studied.
Anyone pregnant or breastfeeding. There isn't enough safety data, so the usual advice is to avoid it.
Anyone with a medical condition or taking regular medication. A quick check with a pharmacist is sensible for any new supplement.

Lion's mane is not a treatment for any medical condition, and it shouldn't replace anything a doctor has prescribed.

Lion's mane and hormones

People often ask whether lion's mane affects estrogen or hormonal contraception. There's no good human evidence either way. We cover what's known, and what isn't, in Mushroom Supplements, Hormones, Estrogen and PCOS. If you use hormonal contraception or HRT, ask your GP or pharmacist before starting.

How much lion's mane do people take?

This is where labels get confusing, because "lion's mane" can mean very different things.

Dried mushroom powder is the whole mushroom, dried and ground. One frequently cited Japanese study gave adults around 3g a day of dried fruiting-body powder for 16 weeks.
Extracts are concentrated. The ratio tells you by how much: a 16:1 extract means around 16g of dried mushroom went into each 1g of extract.
Mycelium products are grown on grain and can contain a lot of starch, so the milligrams on the label may not be mostly mushroom. Here's the difference between fruiting body and mycelium.

So 1,000mg of one product and 1,000mg of another aren't comparable. When you compare, check three things: fruiting body or mycelium, the extraction ratio, and the beta-glucan percentage (why beta-glucans matter).

Practical tips

Follow the label. Don't take more than the stated serving.
Start low if you're sensitive. Half a serving for the first few days, with food.
Take it earlier in the day. Most people take it in the morning or early afternoon, often with coffee. More on timing.
Give it time and keep it consistent. Lion's mane isn't a stimulant; people take it daily and judge it over a few weeks. How long mushroom supplements take to work.

Can you take lion's mane with coffee?

There's no known interaction between lion's mane and caffeine, and many people take them together. If coffee already makes you jittery, keep your usual amount the same when you start lion's mane so you can tell what's what.

Is it safe to take lion's mane every day?

In published trials, adults have taken it daily for several months without serious side effects being reported. There isn't long-term data beyond that. If you take it for months at a time, a periodic check-in with yourself, and your GP if you have health conditions, is reasonable.

Why quality matters for side effects

Some side effects people blame on lion's mane may come from what else is in the capsule: fillers, grain starch from mycelium products, or contaminants in untested supplements. Look for:

Fruiting body only, not mycelium on grain
A stated extraction ratio and dose per serving
Published beta-glucan content
Independent lab testing with results you can see
Organic certification

Comparing brands? Read our buyer's guide to the best lion's mane supplement in the UK.

Health Lovers Organic Lion's Mane

100% organic lion's mane fruiting-body extract, dual extracted at 16:1
2g of extract per serving (two capsules or one teaspoon of powder), 30 servings
35%+ beta-glucans; no mycelium, grain or fillers
Third-party tested by Eurofins, with results on the product page
BDA UK certified and EU organic certified; vegan

See Organic Lion's Mane – capsules or powder

Want focus, energy and calm covered in one? Our 3 Mushroom SuperBlend combines lion's mane with cordyceps and reishi.

FAQ

What are the most common lion's mane side effects?

Mild stomach discomfort and loose stools are the most commonly mentioned. Headaches and allergic reactions have been reported but are uncommon.

Who should not take lion's mane?

People with mushroom allergies, and anyone pregnant or breastfeeding. If you take blood thinners, diabetes medication or immunosuppressants, speak to your GP or pharmacist first.

Can lion's mane cause anxiety?

Some people report feeling restless online, but this hasn't been seen consistently in clinical trials. If you feel unwell, stop taking it.

Does lion's mane interact with medication?

Few human studies have looked at interactions. The main precautionary concerns are blood thinners, diabetes medicines and immunosuppressants. Always tell your pharmacist about supplements you take.

How much lion's mane should I take a day?

Follow the serving on the label, because strength varies widely between products. For Health Lovers Lion's Mane, one serving is 2g of 16:1 extract: two capsules or one teaspoon.

Can I take lion's mane when pregnant?

There isn't enough safety data, so it's usually best avoided during pregnancy and breastfeeding.

Does lion's mane affect the liver?

No liver problems have been reported in the published human trials, and a 2025 rat study found no liver damage at very high doses. If you have a liver condition, check with your doctor first.

Food supplement. Not intended to diagnose, treat, cure or prevent any disease. Not a substitute for a varied and balanced diet. This article is general information, not medical advice. Speak to your GP or pharmacist before use if you are pregnant, breastfeeding, taking medication or have a medical condition.