Guide
Lion's mane side effects
Reported side effects are stomach discomfort, headache, nausea, skin rash and allergic reactions, though they are commonly unreported. Mushroom allergy is the clear caution.
Lion's mane is generally reported to be tolerated, and side effects are rarely documented. The ones listed in a 2025 systematic review were stomach discomfort, headache and allergic reactions, noted as commonly unreported. Allergy is the one to take seriously: do not use it if you are allergic to mushrooms.
What has been reported
A 2025 systematic review of lion's mane studies listed stomach discomfort, headache and allergic reactions as potential side effects, and said they are commonly unreported, so the real rate is unknown (PMID 40959699). Trial data are limited and mostly short:
- In a 49-week trial of about 1,050 mg a day of a standardized lion's mane mycelium, in people with a diagnosed condition, four participants withdrew because of abdominal discomfort, nausea or skin rash, and no other adverse events were reported (PMID 32581767).
- In a 16-week trial of about 3 g a day of lion's mane powder in 30 older adults, laboratory tests showed no adverse effect (PMID 18844328).
These are small trials, often run by people connected to the product, and they cannot rule out rarer reactions. We have not found a long-term study of lion's mane at capsule doses in healthy adults.
Allergy
Lion's mane is a mushroom. Our label warns: do not use if allergic to mushrooms. The systematic review lists allergic reactions among possible effects. If you get itching, hives, swelling, or trouble breathing, stop and get medical help.
Ours specifically
Lion's Mane Mushroom is 1,000 mg of mushroom powder per two capsules, in a pullulan capsule with organic pea starch, as low as $18.23 a bottle on subscription. It is not an extract. The label asks anyone pregnant or nursing, under 18, on medication or with a medical condition to ask a physician first. Pea starch is listed as an other ingredient; it is not an allergen line on the label, but check the panel if you have a pea sensitivity.
Questions people ask
What are the side effects of lion's mane, mushroom or supplement?
Reported ones are stomach discomfort, nausea, headache, skin rash and allergic reactions (PMIDs 40959699, 32581767). Side effects of gummies are not separately studied; they depend on the other ingredients in the product.
Can lion's mane cause dizziness?
We found no trial reporting dizziness as an effect of lion's mane. It is not among the side effects listed in the review above. Dizziness has many causes. If it begins after you start any supplement, stop and speak to a doctor.
Will lion's mane make me sleepy?
We found no study showing that it makes people sleepy, and none designed to test it. We make no claim about sleep or alertness for our product. If you feel unusually drowsy after taking it, stop and talk to a doctor.
Does lion's mane have effects on the liver, and what is meant by uses and side effects?
We found no human study showing liver harm, and none designed to look for it. In the 16-week older-adult trial above, laboratory tests showed no adverse effect (PMID 18844328), but that is one small trial. If you have liver disease, ask your doctor first. For why people take it, see lion's mane benefits: what the research does and doesn't show.
What to do
Start with the label amount, with food if your stomach is sensitive, and stop if anything unusual happens. Read who should not take lion's mane and lion's mane and medications. Seek medical help for any serious reaction.
Sources
- Benefits, side effects, and uses of Hericium erinaceus as a supplement: a systematic review A 2025 review of lion's mane studies listed stomach discomfort, headache and allergic reactions as possible side effects and noted they are commonly unreported.
- Prevention of Early Alzheimer's Disease by Erinacine A-Enriched Hericium erinaceus Mycelia Pilot Double-Blind Placebo-Controlled Study In adults with mild Alzheimer's disease, about 1,050 mg a day of an erinacine A-enriched mycelium for 49 weeks scored better than placebo on some tests; four stopped for stomach or skin reasons.
- Improving effects of the mushroom Yamabushitake (Hericium erinaceus) on mild cognitive impairment: a double-blind placebo-controlled clinical trial In 30 older adults with diagnosed mild cognitive impairment, about 3 g a day of lion's mane powder for 16 weeks raised one cognitive score, which fell back after stopping.
*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.
