Lion’s Mane Mushroom: Possible Side Effects You Should Know About

Angela Gioffre Nutritionist with 25 years of experience.

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Lion’s Mane mushroom (Hericium erinaceus) is well-known for its wellness benefits. With its cascading white tendrils and rich medicinal history, it has become a popular choice in functional nutrition and natural health.

While it is generally considered safe and well-tolerated for most people, some individuals may experience side effects. Understanding these possible reactions is important so you can make informed decisions about your health.

1. Digestive Upset

What can happen:

• Mild bloating

• Soft stools or diarrhoea

• Abdominal cramping

Why it happens:
Lion’s Mane contains bioactive compounds, beta-glucans, and polysaccharides that can alter gut microbiota activity. In some sensitive people, especially when starting at a high dose, this can lead to temporary digestive changes.

How to reduce the risk:

• Start with a small dose and gradually increase.

• Take with food to minimise stomach irritation.

2. Allergic Reactions

What can happen:

• Skin rashes

• Itching

• Breathing difficulties (very rare)

Why it happens:
Allergic reactions can occur with any mushroom species, particularly in individuals with existing mushroom allergies. Even in those without a known allergy, immune hypersensitivity is possible.

How to reduce the risk:

• Try a very small amount first if you have never consumed Lion’s Mane.

• Discontinue use immediately if symptoms occur and seek medical help.

3. Possible Blood Sugar Effects

What can happen:

• Slight lowering of blood glucose

Why it happens:
Some research suggests Lion’s Mane may influence glucose metabolism. While this can be beneficial for many, it may cause issues for people on diabetes medications or those prone to hypoglycaemia.

How to reduce the risk:

• Monitor blood sugar closely if you have diabetes or reactive hypoglycaemia.

• Consult your healthcare provider before use.

4. Interaction with Blood Clotting

What can happen:

• Potential mild blood-thinning effect (theoretical risk)

Why it happens:
Certain mushroom compounds may influence platelet aggregation. While human evidence is limited, this could increase bleeding risk for those on anticoagulants.

How to reduce the risk:

• Avoid high doses before surgery.

• Check with a practitioner if you’re on blood-thinning medications.

5. Unusual Sensations

What can happen:

• Tingling or “nerve zaps”

Why it happens:
Lion’s Mane supports nerve growth factor (NGF) activity. In rare cases, people report mild tingling in the skin or scalp — likely due to increased nerve sensitivity or regeneration processes.

How to reduce the risk:

• Lower the dose if the sensation is uncomfortable.

• These effects are usually temporary.