Is lion's mane safe? Side effects, risks and who should avoid it

How safe is lion’s mane?

As far as anyone can tell, quite safe for healthy adults. It is eaten as a food across East Asia, and across the ten human trials, which gave up to 10 g a day for four weeks or about 1 g a day for nearly a year, no serious side effects were reported. A 2025 systematic review lists stomach discomfort, headache and allergic reactions as the possible side effects, while noting that trials often do not report side effects in detail.

Animal safety studies agree. Rats given lion’s mane powders or extracts at up to 2,000 mg per kg of body weight a day for 90 days, many times the human dose, showed no signs of harm, and the products did not damage DNA in standard tests.

What are the side effects?

Reported side effects are uncommon and usually mild:

• Stomach upset, such as nausea, bloating or loose stools, especially with larger doses or on an empty stomach.
• Headache.
• Skin rash or itching, which may be a sign of allergy and means you should stop.

See side effects for what to do about each, and when to get help.

Who should avoid lion’s mane?

• People allergic to mushrooms or moulds. Lion’s mane is a fungus, and allergic reactions are among the side effects reported with it.
• Pregnant or breastfeeding women. There is no safety data. Eating the mushroom occasionally as food is unlikely to matter, but avoid supplements.
• Children. No safety data, and no reason to give it.
• People having cancer treatment. A mushroom supplement may interact with chemotherapy and complicate liver monitoring. In one 2025 case, a woman on chemotherapy developed liver damage while taking a mixed mushroom powder; the authors blamed a different mushroom in the blend, but it shows why your cancer team needs to know.
• People taking diabetes medicines or drugs that suppress the immune system. In animal and lab studies, lion’s mane extracts lowered blood sugar and acted on immune cells. No interaction has been confirmed in people, but nobody has checked either, so ask your pharmacist first.
• Anyone due for surgery. Tell your surgical team about every supplement you take, and follow their advice on stopping.

Is the product itself safe?

The bigger risk with any supplement is often what else is in it. Mushroom powders can carry heavy metals or pesticide residues from where they were grown, and some products are mostly grain filler. Buy from a seller who publishes recent lab tests for contaminants, and see our buying guide.